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Merge pull request #9497 from edolstra/move-access-control

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Move restricted/pure-eval access control out of the evaluator and into the accessor
This commit is contained in:
Robert Hensing 2023-12-08 22:21:50 +01:00 committed by GitHub
commit d4f6b1d38b
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GPG key ID: 4AEE18F83AFDEB23
23 changed files with 412 additions and 305 deletions
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7
src/libcmd/installables.cc
View file

@ -260,9 +260,10 @@ void SourceExprCommand::completeInstallable(AddCompletions & completions, std::s
evalSettings.pureEval = false;
auto state = getEvalState();
Expr *e = state->parseExprFromFile(
resolveExprPath(state->checkSourcePath(lookupFileArg(*state, *file)))
);
auto e =
state->parseExprFromFile(
resolveExprPath(
lookupFileArg(*state, *file)));
Value root;
state->eval(e, root);

106
src/libexpr/eval.cc
View file

@ -14,6 +14,7 @@
#include "profiles.hh"
#include "print.hh"
#include "fs-input-accessor.hh"
#include "filtering-input-accessor.hh"
#include "memory-input-accessor.hh"
#include "signals.hh"
#include "gc-small-vector.hh"
@ -509,7 +510,16 @@ EvalState::EvalState(
, sOutputSpecified(symbols.create("outputSpecified"))
, repair(NoRepair)
, emptyBindings(0)
, rootFS(makeFSInputAccessor(CanonPath::root))
, rootFS(
evalSettings.restrictEval || evalSettings.pureEval
? ref<InputAccessor>(AllowListInputAccessor::create(makeFSInputAccessor(CanonPath::root), {},
[](const CanonPath & path) -> RestrictedPathError {
auto modeInformation = evalSettings.pureEval
? "in pure evaluation mode (use '--impure' to override)"
: "in restricted mode";
throw RestrictedPathError("access to absolute path '%1%' is forbidden %2%", path, modeInformation);
}))
: makeFSInputAccessor(CanonPath::root))
, corepkgsFS(makeMemoryInputAccessor())
, internalFS(makeMemoryInputAccessor())
, derivationInternal{corepkgsFS->addFile(
@ -551,28 +561,10 @@ EvalState::EvalState(
searchPath.elements.emplace_back(SearchPath::Elem::parse(i));
}
if (evalSettings.restrictEval || evalSettings.pureEval) {
allowedPaths = PathSet();
for (auto & i : searchPath.elements) {
auto r = resolveSearchPathPath(i.path);
if (!r) continue;
auto path = std::move(*r);
if (store->isInStore(path)) {
try {
StorePathSet closure;
store->computeFSClosure(store->toStorePath(path).first, closure);
for (auto & path : closure)
allowPath(path);
} catch (InvalidPath &) {
allowPath(path);
}
} else
allowPath(path);
}
}
/* Allow access to all paths in the search path. */
if (rootFS.dynamic_pointer_cast<AllowListInputAccessor>())
for (auto & i : searchPath.elements)
resolveSearchPathPath(i.path, true);
corepkgsFS->addFile(
CanonPath("fetchurl.nix"),
@ -590,14 +582,14 @@ EvalState::~EvalState()
void EvalState::allowPath(const Path & path)
{
if (allowedPaths)
allowedPaths->insert(path);
if (auto rootFS2 = rootFS.dynamic_pointer_cast<AllowListInputAccessor>())
rootFS2->allowPath(CanonPath(path));
}
void EvalState::allowPath(const StorePath & storePath)
{
if (allowedPaths)
allowedPaths->insert(store->toRealPath(storePath));
if (auto rootFS2 = rootFS.dynamic_pointer_cast<AllowListInputAccessor>())
rootFS2->allowPath(CanonPath(store->toRealPath(storePath)));
}
void EvalState::allowAndSetStorePathString(const StorePath & storePath, Value & v)
@ -607,54 +599,6 @@ void EvalState::allowAndSetStorePathString(const StorePath & storePath, Value &
mkStorePathString(storePath, v);
}
SourcePath EvalState::checkSourcePath(const SourcePath & path_)
{
// Don't check non-rootFS accessors, they're in a different namespace.
if (path_.accessor != ref<InputAccessor>(rootFS)) return path_;
if (!allowedPaths) return path_;
auto i = resolvedPaths.find(path_.path.abs());
if (i != resolvedPaths.end())
return i->second;
bool found = false;
/* First canonicalize the path without symlinks, so we make sure an
* attacker can't append ../../... to a path that would be in allowedPaths
* and thus leak symlink targets.
*/
Path abspath = canonPath(path_.path.abs());
for (auto & i : *allowedPaths) {
if (isDirOrInDir(abspath, i)) {
found = true;
break;
}
}
if (!found) {
auto modeInformation = evalSettings.pureEval
? "in pure eval mode (use '--impure' to override)"
: "in restricted mode";
throw RestrictedPathError("access to absolute path '%1%' is forbidden %2%", abspath, modeInformation);
}
/* Resolve symlinks. */
debug("checking access to '%s'", abspath);
SourcePath path = rootPath(CanonPath(canonPath(abspath, true)));
for (auto & i : *allowedPaths) {
if (isDirOrInDir(path.path.abs(), i)) {
resolvedPaths.insert_or_assign(path_.path.abs(), path);
return path;
}
}
throw RestrictedPathError("access to canonical path '%1%' is forbidden in restricted mode", path);
}
void EvalState::checkURI(const std::string & uri)
{
if (!evalSettings.restrictEval) return;
@ -674,12 +618,14 @@ void EvalState::checkURI(const std::string & uri)
/* If the URI is a path, then check it against allowedPaths as
well. */
if (hasPrefix(uri, "/")) {
checkSourcePath(rootPath(CanonPath(uri)));
if (auto rootFS2 = rootFS.dynamic_pointer_cast<AllowListInputAccessor>())
rootFS2->checkAccess(CanonPath(uri));
return;
}
if (hasPrefix(uri, "file://")) {
checkSourcePath(rootPath(CanonPath(std::string(uri, 7))));
if (auto rootFS2 = rootFS.dynamic_pointer_cast<AllowListInputAccessor>())
rootFS2->checkAccess(CanonPath(uri.substr(7)));
return;
}
@ -1181,10 +1127,8 @@ Value * ExprPath::maybeThunk(EvalState & state, Env & env)
}
void EvalState::evalFile(const SourcePath & path_, Value & v, bool mustBeTrivial)
void EvalState::evalFile(const SourcePath & path, Value & v, bool mustBeTrivial)
{
auto path = checkSourcePath(path_);
FileEvalCache::iterator i;
if ((i = fileEvalCache.find(path)) != fileEvalCache.end()) {
v = i->second;
@ -1205,7 +1149,7 @@ void EvalState::evalFile(const SourcePath & path_, Value & v, bool mustBeTrivial
e = j->second;
if (!e)
e = parseExprFromFile(checkSourcePath(resolvedPath));
e = parseExprFromFile(resolvedPath);
fileParseCache[resolvedPath] = e;

28
src/libexpr/eval.hh
View file

@ -30,7 +30,6 @@ class EvalState;
class StorePath;
struct SingleDerivedPath;
enum RepairFlag : bool;
struct FSInputAccessor;
struct MemoryInputAccessor;
@ -217,18 +216,12 @@ public:
*/
RepairFlag repair;
/**
* The allowed filesystem paths in restricted or pure evaluation
* mode.
*/
std::optional<PathSet> allowedPaths;
Bindings emptyBindings;
/**
* The accessor for the root filesystem.
*/
const ref<FSInputAccessor> rootFS;
const ref<InputAccessor> rootFS;
/**
* The in-memory filesystem for <nix/...> paths.
@ -396,12 +389,6 @@ public:
*/
void allowAndSetStorePathString(const StorePath & storePath, Value & v);
/**
* Check whether access to a path is allowed and throw an error if
* not. Otherwise return the canonicalised path.
*/
SourcePath checkSourcePath(const SourcePath & path);
void checkURI(const std::string & uri);
/**
@ -445,13 +432,15 @@ public:
SourcePath findFile(const SearchPath & searchPath, const std::string_view path, const PosIdx pos = noPos);
/**
* Try to resolve a search path value (not the optional key part)
* Try to resolve a search path value (not the optional key part).
*
* If the specified search path element is a URI, download it.
*
* If it is not found, return `std::nullopt`
*/
std::optional<std::string> resolveSearchPathPath(const SearchPath::Path & path);
std::optional<std::string> resolveSearchPathPath(
const SearchPath::Path & elem,
bool initAccessControl = false);
/**
* Evaluate an expression to normal form
@ -756,6 +745,13 @@ public:
*/
[[nodiscard]] StringMap realiseContext(const NixStringContext & context);
/* Call the binary path filter predicate used builtins.path etc. */
bool callPathFilter(
Value * filterFun,
const SourcePath & path,
std::string_view pathArg,
PosIdx pos);
private:
/**

30
src/libexpr/parser.y
View file

@ -692,16 +692,17 @@ SourcePath resolveExprPath(SourcePath path)
/* If `path' is a symlink, follow it. This is so that relative
path references work. */
while (true) {
while (!path.path.isRoot()) {
// Basic cycle/depth limit to avoid infinite loops.
if (++followCount >= maxFollow)
throw Error("too many symbolic links encountered while traversing the path '%s'", path);
if (path.lstat().type != InputAccessor::tSymlink) break;
path = {path.accessor, CanonPath(path.readLink(), path.path.parent().value_or(CanonPath::root))};
auto p = path.parent().resolveSymlinks() + path.baseName();
if (p.lstat().type != InputAccessor::tSymlink) break;
path = {path.accessor, CanonPath(p.readLink(), path.path.parent().value_or(CanonPath::root))};
}
/* If `path' refers to a directory, append `/default.nix'. */
if (path.lstat().type == InputAccessor::tDirectory)
if (path.resolveSymlinks().lstat().type == InputAccessor::tDirectory)
return path + "default.nix";
return path;
@ -716,7 +717,7 @@ Expr * EvalState::parseExprFromFile(const SourcePath & path)
Expr * EvalState::parseExprFromFile(const SourcePath & path, std::shared_ptr<StaticEnv> & staticEnv)
{
auto buffer = path.readFile();
auto buffer = path.resolveSymlinks().readFile();
// readFile hopefully have left some extra space for terminators
buffer.append("\0\0", 2);
return parse(buffer.data(), buffer.size(), Pos::Origin(path), path.parent(), staticEnv);
@ -783,7 +784,7 @@ SourcePath EvalState::findFile(const SearchPath & searchPath, const std::string_
}
std::optional<std::string> EvalState::resolveSearchPathPath(const SearchPath::Path & value0)
std::optional<std::string> EvalState::resolveSearchPathPath(const SearchPath::Path & value0, bool initAccessControl)
{
auto & value = value0.s;
auto i = searchPathResolved.find(value);
@ -800,7 +801,6 @@ std::optional<std::string> EvalState::resolveSearchPathPath(const SearchPath::Pa
logWarning({
.msg = hintfmt("Nix search path entry '%1%' cannot be downloaded, ignoring", value)
});
res = std::nullopt;
}
}
@ -814,6 +814,20 @@ std::optional<std::string> EvalState::resolveSearchPathPath(const SearchPath::Pa
else {
auto path = absPath(value);
/* Allow access to paths in the search path. */
if (initAccessControl) {
allowPath(path);
if (store->isInStore(path)) {
try {
StorePathSet closure;
store->computeFSClosure(store->toStorePath(path).first, closure);
for (auto & p : closure)
allowPath(p);
} catch (InvalidPath &) { }
}
}
if (pathExists(path))
res = { path };
else {
@ -829,7 +843,7 @@ std::optional<std::string> EvalState::resolveSearchPathPath(const SearchPath::Pa
else
debug("failed to resolve search path element '%s'", value);
searchPathResolved[value] = res;
searchPathResolved.emplace(value, res);
return res;
}

122
src/libexpr/primops.cc
View file

@ -15,6 +15,7 @@
#include "value-to-json.hh"
#include "value-to-xml.hh"
#include "primops.hh"
#include "fs-input-accessor.hh"
#include <boost/container/small_vector.hpp>
#include <nlohmann/json.hpp>
@ -90,9 +91,8 @@ StringMap EvalState::realiseContext(const NixStringContext & context)
for (auto & [outputName, outputPath] : outputs) {
/* Add the output of this derivations to the allowed
paths. */
if (allowedPaths) {
allowPath(outputPath);
}
allowPath(store->toRealPath(outputPath));
/* Get all the output paths corresponding to the placeholders we had */
if (experimentalFeatureSettings.isEnabled(Xp::CaDerivations)) {
res.insert_or_assign(
@ -110,27 +110,19 @@ StringMap EvalState::realiseContext(const NixStringContext & context)
return res;
}
struct RealisePathFlags {
// Whether to check that the path is allowed in pure eval mode
bool checkForPureEval = true;
};
static SourcePath realisePath(EvalState & state, const PosIdx pos, Value & v, const RealisePathFlags flags = {})
static SourcePath realisePath(EvalState & state, const PosIdx pos, Value & v, bool resolveSymlinks = true)
{
NixStringContext context;
auto path = state.coerceToPath(noPos, v, context, "while realising the context of a path");
try {
if (!context.empty()) {
if (!context.empty() && path.accessor == state.rootFS) {
auto rewrites = state.realiseContext(context);
auto realPath = state.toRealPath(rewriteStrings(path.path.abs(), rewrites), context);
return {path.accessor, CanonPath(realPath)};
path = {path.accessor, CanonPath(realPath)};
}
return flags.checkForPureEval
? state.checkSourcePath(path)
: path;
return resolveSymlinks ? path.resolveSymlinks() : path;
} catch (Error & e) {
e.addTrace(state.positions[pos], "while realising the context of path '%s'", path);
throw;
@ -170,7 +162,7 @@ static void mkOutputString(
argument. */
static void import(EvalState & state, const PosIdx pos, Value & vPath, Value * vScope, Value & v)
{
auto path = realisePath(state, pos, vPath);
auto path = realisePath(state, pos, vPath, false);
auto path2 = path.path.abs();
// FIXME
@ -1493,7 +1485,7 @@ static void prim_storePath(EvalState & state, const PosIdx pos, Value * * args,
}));
NixStringContext context;
auto path = state.checkSourcePath(state.coerceToPath(pos, *args[0], context, "while evaluating the first argument passed to 'builtins.storePath'")).path;
auto path = state.coerceToPath(pos, *args[0], context, "while evaluating the first argument passed to 'builtins.storePath'").path;
/* Resolve symlinks in ‘path’, unless ‘path’ itself is a symlink
directly in the store. The latter condition is necessary so
e.g. nix-push does the right thing. */
@ -1533,29 +1525,19 @@ static RegisterPrimOp primop_storePath({
static void prim_pathExists(EvalState & state, const PosIdx pos, Value * * args, Value & v)
{
try {
auto & arg = *args[0];
/* We don’t check the path right now, because we don’t want to
throw if the path isn’t allowed, but just return false (and we
can’t just catch the exception here because we still want to
throw if something in the evaluation of `arg` tries to
access an unauthorized path). */
auto path = realisePath(state, pos, arg, { .checkForPureEval = false });
auto path = realisePath(state, pos, arg);
/* SourcePath doesn't know about trailing slash. */
auto mustBeDir = arg.type() == nString
&& (arg.string_view().ends_with("/")
|| arg.string_view().ends_with("/."));
try {
auto checked = state.checkSourcePath(path);
auto st = checked.maybeLstat();
auto st = path.maybeLstat();
auto exists = st && (!mustBeDir || st->type == SourceAccessor::tDirectory);
v.mkBool(exists);
} catch (SysError & e) {
/* Don't give away info from errors while canonicalising
‘path’ in restricted mode. */
v.mkBool(false);
} catch (RestrictedPathError & e) {
v.mkBool(false);
}
@ -1699,7 +1681,7 @@ static void prim_findFile(EvalState & state, const PosIdx pos, Value * * args, V
auto path = state.forceStringNoCtx(*args[1], pos, "while evaluating the second argument passed to builtins.findFile");
v.mkPath(state.checkSourcePath(state.findFile(searchPath, path, pos)));
v.mkPath(state.findFile(searchPath, path, pos));
}
static RegisterPrimOp primop_findFile(PrimOp {
@ -1789,7 +1771,7 @@ static std::string_view fileTypeToString(InputAccessor::Type type)
static void prim_readFileType(EvalState & state, const PosIdx pos, Value * * args, Value & v)
{
auto path = realisePath(state, pos, *args[0]);
auto path = realisePath(state, pos, *args[0], false);
/* Retrieve the directory entry type and stringize it. */
v.mkString(fileTypeToString(path.lstat().type));
}
@ -2178,11 +2160,35 @@ static RegisterPrimOp primop_toFile({
.fun = prim_toFile,
});
bool EvalState::callPathFilter(
Value * filterFun,
const SourcePath & path,
std::string_view pathArg,
PosIdx pos)
{
auto st = path.lstat();
/* Call the filter function. The first argument is the path, the
second is a string indicating the type of the file. */
Value arg1;
arg1.mkString(pathArg);
Value arg2;
// assert that type is not "unknown"
arg2.mkString(fileTypeToString(st.type));
Value * args []{&arg1, &arg2};
Value res;
callFunction(*filterFun, 2, args, res, pos);
return forceBool(res, pos, "while evaluating the return value of the path filter function");
}
static void addPath(
EvalState & state,
const PosIdx pos,
std::string_view name,
Path path,
SourcePath path,
Value * filterFun,
FileIngestionMethod method,
const std::optional<Hash> expectedHash,
@ -2190,48 +2196,29 @@ static void addPath(
const NixStringContext & context)
{
try {
StorePathSet refs;
if (path.accessor == state.rootFS && state.store->isInStore(path.path.abs())) {
// FIXME: handle CA derivation outputs (where path needs to
// be rewritten to the actual output).
auto rewrites = state.realiseContext(context);
path = state.toRealPath(rewriteStrings(path, rewrites), context);
path = {state.rootFS, CanonPath(state.toRealPath(rewriteStrings(path.path.abs(), rewrites), context))};
StorePathSet refs;
if (state.store->isInStore(path)) {
try {
auto [storePath, subPath] = state.store->toStorePath(path);
auto [storePath, subPath] = state.store->toStorePath(path.path.abs());
// FIXME: we should scanForReferences on the path before adding it
refs = state.store->queryPathInfo(storePath)->references;
path = state.store->toRealPath(storePath) + subPath;
path = {state.rootFS, CanonPath(state.store->toRealPath(storePath) + subPath)};
} catch (Error &) { // FIXME: should be InvalidPathError
}
}
path = evalSettings.pureEval && expectedHash
? path
: state.checkSourcePath(state.rootPath(CanonPath(path))).path.abs();
PathFilter filter = filterFun ? ([&](const Path & path) {
auto st = lstat(path);
/* Call the filter function. The first argument is the path,
the second is a string indicating the type of the file. */
Value arg1;
arg1.mkString(path);
Value arg2;
arg2.mkString(
S_ISREG(st.st_mode) ? "regular" :
S_ISDIR(st.st_mode) ? "directory" :
S_ISLNK(st.st_mode) ? "symlink" :
"unknown" /* not supported, will fail! */);
Value * args []{&arg1, &arg2};
Value res;
state.callFunction(*filterFun, 2, args, res, pos);
return state.forceBool(res, pos, "while evaluating the return value of the path filter function");
}) : defaultPathFilter;
std::unique_ptr<PathFilter> filter;
if (filterFun)
filter = std::make_unique<PathFilter>([&](const Path & p) {
auto p2 = CanonPath(p);
return state.callPathFilter(filterFun, {path.accessor, p2}, p2.abs(), pos);
});
std::optional<StorePath> expectedStorePath;
if (expectedHash)
@ -2242,7 +2229,7 @@ static void addPath(
});
if (!expectedHash || !state.store->isValidPath(*expectedStorePath)) {
auto dstPath = state.rootPath(CanonPath(path)).fetchToStore(state.store, name, method, &filter, state.repair);
auto dstPath = path.fetchToStore(state.store, name, method, filter.get(), state.repair);
if (expectedHash && expectedStorePath != dstPath)
state.debugThrowLastTrace(Error("store path mismatch in (possibly filtered) path added from '%s'", path));
state.allowAndSetStorePathString(dstPath, v);
@ -2261,7 +2248,8 @@ static void prim_filterSource(EvalState & state, const PosIdx pos, Value * * arg
auto path = state.coerceToPath(pos, *args[1], context,
"while evaluating the second argument (the path to filter) passed to 'builtins.filterSource'");
state.forceFunction(*args[0], pos, "while evaluating the first argument passed to builtins.filterSource");
addPath(state, pos, path.baseName(), path.path.abs(), args[0], FileIngestionMethod::Recursive, std::nullopt, v, context);
addPath(state, pos, path.baseName(), path, args[0], FileIngestionMethod::Recursive, std::nullopt, v, context);
}
static RegisterPrimOp primop_filterSource({
@ -2356,7 +2344,7 @@ static void prim_path(EvalState & state, const PosIdx pos, Value * * args, Value
if (name.empty())
name = path->baseName();
addPath(state, pos, name, path->path.abs(), filterFun, method, expectedHash, v, context);
addPath(state, pos, name, *path, filterFun, method, expectedHash, v, context);
}
static RegisterPrimOp primop_path({

7
src/libexpr/value.hh
View file

@ -423,10 +423,9 @@ public:
SourcePath path() const
{
assert(internalType == tPath);
return SourcePath {
.accessor = ref(_path.accessor->shared_from_this()),
.path = CanonPath(CanonPath::unchecked_t(), _path.path)
};
return SourcePath(
ref(_path.accessor->shared_from_this()),
CanonPath(CanonPath::unchecked_t(), _path.path));
}
std::string_view string_view() const

2
src/libfetchers/fetchers.cc
View file

@ -374,7 +374,7 @@ void InputScheme::clone(const Input & input, const Path & destDir) const
std::pair<StorePath, Input> InputScheme::fetch(ref<Store> store, const Input & input)
{
auto [accessor, input2] = getAccessor(store, input);
auto storePath = accessor->root().fetchToStore(store, input2.getName());
auto storePath = SourcePath(accessor).fetchToStore(store, input2.getName());
return {storePath, input2};
}

83
src/libfetchers/filtering-input-accessor.cc Normal file
View file

@ -0,0 +1,83 @@
#include "filtering-input-accessor.hh"
namespace nix {
std::string FilteringInputAccessor::readFile(const CanonPath & path)
{
checkAccess(path);
return next->readFile(prefix + path);
}
bool FilteringInputAccessor::pathExists(const CanonPath & path)
{
return isAllowed(path) && next->pathExists(prefix + path);
}
std::optional<InputAccessor::Stat> FilteringInputAccessor::maybeLstat(const CanonPath & path)
{
checkAccess(path);
return next->maybeLstat(prefix + path);
}
InputAccessor::DirEntries FilteringInputAccessor::readDirectory(const CanonPath & path)
{
checkAccess(path);
DirEntries entries;
for (auto & entry : next->readDirectory(prefix + path)) {
if (isAllowed(path + entry.first))
entries.insert(std::move(entry));
}
return entries;
}
std::string FilteringInputAccessor::readLink(const CanonPath & path)
{
checkAccess(path);
return next->readLink(prefix + path);
}
std::string FilteringInputAccessor::showPath(const CanonPath & path)
{
return next->showPath(prefix + path);
}
void FilteringInputAccessor::checkAccess(const CanonPath & path)
{
if (!isAllowed(path))
throw makeNotAllowedError
? makeNotAllowedError(path)
: RestrictedPathError("access to path '%s' is forbidden", showPath(path));
}
struct AllowListInputAccessorImpl : AllowListInputAccessor
{
std::set<CanonPath> allowedPaths;
AllowListInputAccessorImpl(
ref<InputAccessor> next,
std::set<CanonPath> && allowedPaths,
MakeNotAllowedError && makeNotAllowedError)
: AllowListInputAccessor(SourcePath(next), std::move(makeNotAllowedError))
, allowedPaths(std::move(allowedPaths))
{ }
bool isAllowed(const CanonPath & path) override
{
return path.isAllowed(allowedPaths);
}
void allowPath(CanonPath path) override
{
allowedPaths.insert(std::move(path));
}
};
ref<AllowListInputAccessor> AllowListInputAccessor::create(
ref<InputAccessor> next,
std::set<CanonPath> && allowedPaths,
MakeNotAllowedError && makeNotAllowedError)
{
return make_ref<AllowListInputAccessorImpl>(next, std::move(allowedPaths), std::move(makeNotAllowedError));
}
}

73
src/libfetchers/filtering-input-accessor.hh Normal file
View file

@ -0,0 +1,73 @@
#pragma once
#include "input-accessor.hh"
namespace nix {
/**
* A function that should throw an exception of type
* `RestrictedPathError` explaining that access to `path` is
* forbidden.
*/
typedef std::function<RestrictedPathError(const CanonPath & path)> MakeNotAllowedError;
/**
* An abstract wrapping `InputAccessor` that performs access
* control. Subclasses should override `isAllowed()` to implement an
* access control policy. The error message is customized at construction.
*/
struct FilteringInputAccessor : InputAccessor
{
ref<InputAccessor> next;
CanonPath prefix;
MakeNotAllowedError makeNotAllowedError;
FilteringInputAccessor(const SourcePath & src, MakeNotAllowedError && makeNotAllowedError)
: next(src.accessor)
, prefix(src.path)
, makeNotAllowedError(std::move(makeNotAllowedError))
{ }
std::string readFile(const CanonPath & path) override;
bool pathExists(const CanonPath & path) override;
std::optional<Stat> maybeLstat(const CanonPath & path) override;
DirEntries readDirectory(const CanonPath & path) override;
std::string readLink(const CanonPath & path) override;
std::string showPath(const CanonPath & path) override;
/**
* Call `makeNotAllowedError` to throw a `RestrictedPathError`
* exception if `isAllowed()` returns `false` for `path`.
*/
void checkAccess(const CanonPath & path);
/**
* Return `true` iff access to path is allowed.
*/
virtual bool isAllowed(const CanonPath & path) = 0;
};
/**
* A wrapping `InputAccessor` that checks paths against an allow-list.
*/
struct AllowListInputAccessor : public FilteringInputAccessor
{
/**
* Grant access to the specified path.
*/
virtual void allowPath(CanonPath path) = 0;
static ref<AllowListInputAccessor> create(
ref<InputAccessor> next,
std::set<CanonPath> && allowedPaths,
MakeNotAllowedError && makeNotAllowedError);
using FilteringInputAccessor::FilteringInputAccessor;
};
}

75
src/libfetchers/fs-input-accessor.cc
View file

@ -4,19 +4,12 @@
namespace nix {
struct FSInputAccessorImpl : FSInputAccessor, PosixSourceAccessor
struct FSInputAccessor : InputAccessor, PosixSourceAccessor
{
CanonPath root;
std::optional<std::set<CanonPath>> allowedPaths;
MakeNotAllowedError makeNotAllowedError;
FSInputAccessorImpl(
const CanonPath & root,
std::optional<std::set<CanonPath>> && allowedPaths,
MakeNotAllowedError && makeNotAllowedError)
FSInputAccessor(const CanonPath & root)
: root(root)
, allowedPaths(std::move(allowedPaths))
, makeNotAllowedError(std::move(makeNotAllowedError))
{
displayPrefix = root.isRoot() ? "" : root.abs();
}
@ -27,39 +20,30 @@ struct FSInputAccessorImpl : FSInputAccessor, PosixSourceAccessor
std::function<void(uint64_t)> sizeCallback) override
{
auto absPath = makeAbsPath(path);
checkAllowed(absPath);
PosixSourceAccessor::readFile(absPath, sink, sizeCallback);
}
bool pathExists(const CanonPath & path) override
{
auto absPath = makeAbsPath(path);
return isAllowed(absPath) && PosixSourceAccessor::pathExists(absPath);
return PosixSourceAccessor::pathExists(makeAbsPath(path));
}
std::optional<Stat> maybeLstat(const CanonPath & path) override
{
auto absPath = makeAbsPath(path);
checkAllowed(absPath);
return PosixSourceAccessor::maybeLstat(absPath);
return PosixSourceAccessor::maybeLstat(makeAbsPath(path));
}
DirEntries readDirectory(const CanonPath & path) override
{
auto absPath = makeAbsPath(path);
checkAllowed(absPath);
DirEntries res;
for (auto & entry : PosixSourceAccessor::readDirectory(absPath))
if (isAllowed(absPath + entry.first))
for (auto & entry : PosixSourceAccessor::readDirectory(makeAbsPath(path)))
res.emplace(entry);
return res;
}
std::string readLink(const CanonPath & path) override
{
auto absPath = makeAbsPath(path);
checkAllowed(absPath);
return PosixSourceAccessor::readLink(absPath);
return PosixSourceAccessor::readLink(makeAbsPath(path));
}
CanonPath makeAbsPath(const CanonPath & path)
@ -67,59 +51,22 @@ struct FSInputAccessorImpl : FSInputAccessor, PosixSourceAccessor
return root + path;
}
void checkAllowed(const CanonPath & absPath) override
{
if (!isAllowed(absPath))
throw makeNotAllowedError
? makeNotAllowedError(absPath)
: RestrictedPathError("access to path '%s' is forbidden", absPath);
}
bool isAllowed(const CanonPath & absPath)
{
if (!absPath.isWithin(root))
return false;
if (allowedPaths) {
auto p = absPath.removePrefix(root);
if (!p.isAllowed(*allowedPaths))
return false;
}
return true;
}
void allowPath(CanonPath path) override
{
if (allowedPaths)
allowedPaths->insert(std::move(path));
}
bool hasAccessControl() override
{
return (bool) allowedPaths;
}
std::optional<CanonPath> getPhysicalPath(const CanonPath & path) override
{
return makeAbsPath(path);
}
};
ref<FSInputAccessor> makeFSInputAccessor(
const CanonPath & root,
std::optional<std::set<CanonPath>> && allowedPaths,
MakeNotAllowedError && makeNotAllowedError)
ref<InputAccessor> makeFSInputAccessor(const CanonPath & root)
{
return make_ref<FSInputAccessorImpl>(root, std::move(allowedPaths), std::move(makeNotAllowedError));
return make_ref<FSInputAccessor>(root);
}
ref<FSInputAccessor> makeStorePathAccessor(
ref<InputAccessor> makeStorePathAccessor(
ref<Store> store,
const StorePath & storePath,
MakeNotAllowedError && makeNotAllowedError)
const StorePath & storePath)
{
return makeFSInputAccessor(CanonPath(store->toRealPath(storePath)), {}, std::move(makeNotAllowedError));
return makeFSInputAccessor(CanonPath(store->toRealPath(storePath)));
}
SourcePath getUnfilteredRootPath(CanonPath path)

22
src/libfetchers/fs-input-accessor.hh
View file

@ -7,26 +7,12 @@ namespace nix {
class StorePath;
class Store;
struct FSInputAccessor : InputAccessor
{
virtual void checkAllowed(const CanonPath & absPath) = 0;
ref<InputAccessor> makeFSInputAccessor(
const CanonPath & root);
virtual void allowPath(CanonPath path) = 0;
virtual bool hasAccessControl() = 0;
};
typedef std::function<RestrictedPathError(const CanonPath & path)> MakeNotAllowedError;
ref<FSInputAccessor> makeFSInputAccessor(
const CanonPath & root,
std::optional<std::set<CanonPath>> && allowedPaths = {},
MakeNotAllowedError && makeNotAllowedError = {});
ref<FSInputAccessor> makeStorePathAccessor(
ref<InputAccessor> makeStorePathAccessor(
ref<Store> store,
const StorePath & storePath,
MakeNotAllowedError && makeNotAllowedError = {});
const StorePath & storePath);
SourcePath getUnfilteredRootPath(CanonPath path);

2
src/libfetchers/git-utils.cc
View file

@ -554,7 +554,7 @@ struct GitInputAccessor : InputAccessor
return toHash(*git_tree_entry_id(entry));
}
std::map<CanonPath, TreeEntry> lookupCache;
std::unordered_map<CanonPath, TreeEntry> lookupCache;
/* Recursively look up 'path' relative to the root. */
git_tree_entry * lookup(const CanonPath & path)

6
src/libfetchers/git.cc
View file

@ -9,6 +9,7 @@
#include "processes.hh"
#include "git.hh"
#include "fs-input-accessor.hh"
#include "filtering-input-accessor.hh"
#include "mounted-input-accessor.hh"
#include "git-utils.hh"
#include "logging.hh"
@ -639,7 +640,10 @@ struct GitInputScheme : InputScheme
repoInfo.workdirInfo.files.insert(submodule.path);
ref<InputAccessor> accessor =
makeFSInputAccessor(CanonPath(repoInfo.url), repoInfo.workdirInfo.files, makeNotAllowedError(repoInfo.url));
AllowListInputAccessor::create(
makeFSInputAccessor(CanonPath(repoInfo.url)),
std::move(repoInfo.workdirInfo.files),
makeNotAllowedError(repoInfo.url));
/* If the repo has submodules, return a mounted input accessor
consisting of the accessor for the top-level repo and the

7
src/libfetchers/input-accessor.cc
View file

@ -53,11 +53,6 @@ StorePath InputAccessor::fetchToStore(
return storePath;
}
SourcePath InputAccessor::root()
{
return {ref(shared_from_this()), CanonPath::root};
}
std::ostream & operator << (std::ostream & str, const SourcePath & path)
{
str << path.to_string();
@ -88,7 +83,7 @@ SourcePath SourcePath::parent() const
SourcePath SourcePath::resolveSymlinks() const
{
auto res = accessor->root();
auto res = SourcePath(accessor);
int linksAllowed = 1024;

7
src/libfetchers/input-accessor.hh
View file

@ -36,8 +36,6 @@ struct InputAccessor : virtual SourceAccessor, std::enable_shared_from_this<Inpu
FileIngestionMethod method = FileIngestionMethod::Recursive,
PathFilter * filter = nullptr,
RepairFlag repair = NoRepair);
SourcePath root();
};
/**
@ -51,6 +49,11 @@ struct SourcePath
ref<InputAccessor> accessor;
CanonPath path;
SourcePath(ref<InputAccessor> accessor, CanonPath path = CanonPath::root)
: accessor(std::move(accessor))
, path(std::move(path))
{ }
std::string_view baseName() const;
/**

11
src/libutil/canon-path.hh
View file

@ -205,8 +205,19 @@ public:
* `CanonPath(this.makeRelative(x), this) == path`.
*/
std::string makeRelative(const CanonPath & path) const;
friend class std::hash<CanonPath>;
};
std::ostream & operator << (std::ostream & stream, const CanonPath & path);
}
template<>
struct std::hash<nix::CanonPath>
{
std::size_t operator ()(const nix::CanonPath & s) const noexcept
{
return std::hash<std::string>{}(s.path);
}
};

67
src/libutil/posix-source-accessor.cc
View file

@ -1,5 +1,8 @@
#include "posix-source-accessor.hh"
#include "signals.hh"
#include "sync.hh"
#include <unordered_map>
namespace nix {
@ -8,9 +11,9 @@ void PosixSourceAccessor::readFile(
Sink & sink,
std::function<void(uint64_t)> sizeCallback)
{
// FIXME: add O_NOFOLLOW since symlinks should be resolved by the
// caller?
AutoCloseFD fd = open(path.c_str(), O_RDONLY | O_CLOEXEC);
assertNoSymlinks(path);
AutoCloseFD fd = open(path.c_str(), O_RDONLY | O_CLOEXEC | O_NOFOLLOW);
if (!fd)
throw SysError("opening file '%1%'", path);
@ -42,30 +45,55 @@ void PosixSourceAccessor::readFile(
bool PosixSourceAccessor::pathExists(const CanonPath & path)
{
if (auto parent = path.parent()) assertNoSymlinks(*parent);
return nix::pathExists(path.abs());
}
std::optional<struct stat> PosixSourceAccessor::cachedLstat(const CanonPath & path)
{
static Sync<std::unordered_map<CanonPath, std::optional<struct stat>>> _cache;
{
auto cache(_cache.lock());
auto i = cache->find(path);
if (i != cache->end()) return i->second;
}
std::optional<struct stat> st{std::in_place};
if (::lstat(path.c_str(), &*st)) {
if (errno == ENOENT || errno == ENOTDIR)
st.reset();
else
throw SysError("getting status of '%s'", showPath(path));
}
auto cache(_cache.lock());
if (cache->size() >= 16384) cache->clear();
cache->emplace(path, st);
return st;
}
std::optional<SourceAccessor::Stat> PosixSourceAccessor::maybeLstat(const CanonPath & path)
{
struct stat st;
if (::lstat(path.c_str(), &st)) {
if (errno == ENOENT) return std::nullopt;
throw SysError("getting status of '%s'", showPath(path));
}
mtime = std::max(mtime, st.st_mtime);
if (auto parent = path.parent()) assertNoSymlinks(*parent);
auto st = cachedLstat(path);
if (!st) return std::nullopt;
mtime = std::max(mtime, st->st_mtime);
return Stat {
.type =
S_ISREG(st.st_mode) ? tRegular :
S_ISDIR(st.st_mode) ? tDirectory :
S_ISLNK(st.st_mode) ? tSymlink :
S_ISREG(st->st_mode) ? tRegular :
S_ISDIR(st->st_mode) ? tDirectory :
S_ISLNK(st->st_mode) ? tSymlink :
tMisc,
.fileSize = S_ISREG(st.st_mode) ? std::optional<uint64_t>(st.st_size) : std::nullopt,
.isExecutable = S_ISREG(st.st_mode) && st.st_mode & S_IXUSR,
.fileSize = S_ISREG(st->st_mode) ? std::optional<uint64_t>(st->st_size) : std::nullopt,
.isExecutable = S_ISREG(st->st_mode) && st->st_mode & S_IXUSR,
};
}
SourceAccessor::DirEntries PosixSourceAccessor::readDirectory(const CanonPath & path)
{
assertNoSymlinks(path);
DirEntries res;
for (auto & entry : nix::readDirectory(path.abs())) {
std::optional<Type> type;
@ -81,6 +109,7 @@ SourceAccessor::DirEntries PosixSourceAccessor::readDirectory(const CanonPath &
std::string PosixSourceAccessor::readLink(const CanonPath & path)
{
if (auto parent = path.parent()) assertNoSymlinks(*parent);
return nix::readLink(path.abs());
}
@ -89,4 +118,14 @@ std::optional<CanonPath> PosixSourceAccessor::getPhysicalPath(const CanonPath &
return path;
}
void PosixSourceAccessor::assertNoSymlinks(CanonPath path)
{
while (!path.isRoot()) {
auto st = cachedLstat(path);
if (st && S_ISLNK(st->st_mode))
throw Error("path '%s' is a symlink", showPath(path));
path.pop();
}
}
}

9
src/libutil/posix-source-accessor.hh
View file

@ -29,6 +29,15 @@ struct PosixSourceAccessor : virtual SourceAccessor
std::string readLink(const CanonPath & path) override;
std::optional<CanonPath> getPhysicalPath(const CanonPath & path) override;
private:
/**
* Throw an error if `path` or any of its ancestors are symlinks.
*/
void assertNoSymlinks(CanonPath path);
std::optional<struct stat> cachedLstat(const CanonPath & path);
};
}

7
src/nix-build/nix-build.cc
View file

@ -311,8 +311,11 @@ static void main_nix_build(int argc, char * * argv)
else
/* If we're in a #! script, interpret filenames
relative to the script. */
exprs.push_back(state->parseExprFromFile(resolveExprPath(state->checkSourcePath(lookupFileArg(*state,
inShebang && !packages ? absPath(i, absPath(dirOf(script))) : i)))));
exprs.push_back(
state->parseExprFromFile(
resolveExprPath(
lookupFileArg(*state,
inShebang && !packages ? absPath(i, absPath(dirOf(script))) : i))));
}
}

6
src/nix-env/nix-env.cc
View file

@ -97,7 +97,7 @@ static bool isNixExpr(const SourcePath & path, struct InputAccessor::Stat & st)
{
return
st.type == InputAccessor::tRegular
|| (st.type == InputAccessor::tDirectory && (path + "default.nix").pathExists());
|| (st.type == InputAccessor::tDirectory && (path + "default.nix").resolveSymlinks().pathExists());
}
@ -116,11 +116,11 @@ static void getAllExprs(EvalState & state,
are implemented using profiles). */
if (i == "manifest.nix") continue;
SourcePath path2 = path + i;
auto path2 = (path + i).resolveSymlinks();
InputAccessor::Stat st;
try {
st = path2.resolveSymlinks().lstat();
st = path2.lstat();
} catch (Error &) {
continue; // ignore dangling symlinks in ~/.nix-defexpr
}

2
src/nix-env/user-env.cc
View file

@ -21,7 +21,7 @@ DrvInfos queryInstalled(EvalState & state, const Path & userEnv)
auto manifestFile = userEnv + "/manifest.nix";
if (pathExists(manifestFile)) {
Value v;
state.evalFile(state.rootPath(CanonPath(manifestFile)), v);
state.evalFile(state.rootPath(CanonPath(manifestFile)).resolveSymlinks(), v);
Bindings & bindings(*state.allocBindings(0));
getDerivations(state, v, "", bindings, elems, false);
}

2
src/nix-instantiate/nix-instantiate.cc
View file

@ -183,7 +183,7 @@ static int main_nix_instantiate(int argc, char * * argv)
for (auto & i : files) {
Expr * e = fromArgs
? state->parseExprFromString(i, state->rootPath(CanonPath::fromCwd()))
: state->parseExprFromFile(resolveExprPath(state->checkSourcePath(lookupFileArg(*state, i))));
: state->parseExprFromFile(resolveExprPath(lookupFileArg(*state, i)));
processExpr(*state, attrPaths, parseOnly, strict, autoArgs,
evalOnly, outputKind, xmlOutputSourceLocation, e);
}

16
tests/functional/restricted.sh
View file

@ -14,8 +14,8 @@ nix-instantiate --restrict-eval --eval -E 'builtins.readFile ./simple.nix' -I sr
(! nix-instantiate --restrict-eval --eval -E 'builtins.readDir ../../src/nix-channel')
nix-instantiate --restrict-eval --eval -E 'builtins.readDir ../../src/nix-channel' -I src=../../src
(! nix-instantiate --restrict-eval --eval -E 'let __nixPath = [ { prefix = "foo"; path = ./.; } ]; in <foo>')
nix-instantiate --restrict-eval --eval -E 'let __nixPath = [ { prefix = "foo"; path = ./.; } ]; in <foo>' -I src=.
expectStderr 1 nix-instantiate --restrict-eval --eval -E 'let __nixPath = [ { prefix = "foo"; path = ./.; } ]; in builtins.readFile <foo/simple.nix>' | grepQuiet "forbidden in restricted mode"
nix-instantiate --restrict-eval --eval -E 'let __nixPath = [ { prefix = "foo"; path = ./.; } ]; in builtins.readFile <foo/simple.nix>' -I src=.
p=$(nix eval --raw --expr "builtins.fetchurl file://$(pwd)/restricted.sh" --impure --restrict-eval --allowed-uris "file://$(pwd)")
cmp $p restricted.sh
@ -39,6 +39,18 @@ nix-instantiate --eval --restrict-eval $TEST_ROOT/restricted.nix -I $TEST_ROOT -
[[ $(nix eval --raw --impure --restrict-eval -I . --expr 'builtins.readFile "${import ./simple.nix}/hello"') == 'Hello World!' ]]
# Check that we can't follow a symlink outside of the allowed paths.
mkdir -p $TEST_ROOT/tunnel.d $TEST_ROOT/foo2
ln -sfn .. $TEST_ROOT/tunnel.d/tunnel
echo foo > $TEST_ROOT/bar
expectStderr 1 nix-instantiate --restrict-eval --eval -E "let __nixPath = [ { prefix = \"foo\"; path = $TEST_ROOT/tunnel.d; } ]; in builtins.readFile <foo/tunnel/bar>" -I $TEST_ROOT/tunnel.d | grepQuiet "forbidden in restricted mode"
expectStderr 1 nix-instantiate --restrict-eval --eval -E "let __nixPath = [ { prefix = \"foo\"; path = $TEST_ROOT/tunnel.d; } ]; in builtins.readDir <foo/tunnel/foo2>" -I $TEST_ROOT/tunnel.d | grepQuiet "forbidden in restricted mode"
# Reading the parents of allowed paths should show only the ancestors of the allowed paths.
[[ $(nix-instantiate --restrict-eval --eval -E "let __nixPath = [ { prefix = \"foo\"; path = $TEST_ROOT/tunnel.d; } ]; in builtins.readDir <foo/tunnel>" -I $TEST_ROOT/tunnel.d) == '{ "tunnel.d" = "directory"; }' ]]
# Check whether we can leak symlink information through directory traversal.
traverseDir="$(pwd)/restricted-traverse-me"
ln -sfn "$(pwd)/restricted-secret" "$(pwd)/restricted-innocent"