In EvalState::checkSourcePath, the path is checked against the list of
allowed paths first and later it's checked again *after* resolving
symlinks.
The resolving of the symlinks is done via canonPath, which also strips
out "../" and "./". However after the canonicalisation the error message
pointing out that the path is not allowed prints the symlink target in
the error message.
Even if we'd suppress the message, symlink targets could still be leaked
if the symlink target doesn't exist (in this case the error is thrown in
canonPath).
So instead, we now do canonPath() without symlink resolving first before
even checking against the list of allowed paths and then later do the
symlink resolving and checking the allowed paths again.
The first call to canonPath() should get rid of all the "../" and "./",
so in theory the only way to leak a symlink if the attacker is able to
put a symlink in one of the paths allowed by restricted evaluation mode.
For the latter I don't think this is part of the threat model, because
if the attacker can write to that path, the attack vector is even
larger.
Signed-off-by: aszlig <aszlig@nix.build>
This reduces the risk of object liveness misdetection. For example,
Glibc has an internal variable "mp_" that often points to a Boehm
object, keeping it alive unnecessarily. Since we don't store any
actual roots in global variables, we can just disable data segment
scanning.
With this, the max RSS doing 100 evaluations of
nixos.tests.firefox.x86_64-linux.drvPath went from 718 MiB to 455 MiB.
If the Env denotes a 'with', then values[0] may be an Expr* cast to a
Value*. For code that generically traverses Values/Envs, it's useful
to know this.
E.g. this makes
nix eval --restrict-eval -I /nix/store/foo '(builtins.readFile "/nix/store/foo/symlink/bla")'
(where /nix/store/foo/symlink is a symlink to another path in the
closure of /nix/store/foo) succeed.
This fixes a regression in Hydra compared to Nix 1.x (where there were
no restrictions at all on access to the Nix store).
Doing so prevents emacs tags from working, as well as makes the code extremely
confusing for a newbie.
In the prior state, if someone wants to find the definition of "ExprApp" for
example, a grep through the code reveals nothing. Since the definition could be
hiding in numerous ".h" files, it's really difficult to find. This personally
took me several hours to figure out.
Flex's regexes have an annoying feature: the dot matches everything
except a newline. This causes problems for expressions like:
"${0}\
"
where the backslash-newline combination matches this rule instead of the
intended one mentioned in the comment:
<STRING>\$|\\|\$\\ {
/* This can only occur when we reach EOF, otherwise the above
(...|\$[^\{\"\\]|\\.|\$\\.)+ would have triggered.
This is technically invalid, but we leave the problem to the
parser who fails with exact location. */
return STR;
}
However, the parser actually accepts the resulting token sequence
('"' DOLLAR_CURLY 0 '}' STR '"'), which is a problem because the lexer
rule didn't assign anything to yylval. Ultimately this leads to a crash
when dereferencing a NULL pointer in ExprConcatStrings::bindVars().
The fix does change the syntax of the language in some corner cases
but I think it's only turning previously invalid (or crashing) syntax
to valid syntax. E.g.
"a\
b"
and
''a''\
b''
were previously syntax errors but now both result in "a\nb".
Found by afl-fuzz.
Otherwise, running e.g.
nix-instantiate --eval -E --strict 'builtins.replaceStrings [""] ["X"] "abc"'
would just hang in an infinite loop.
Found by afl-fuzz.
First attempt of this was reverted in e2d71bd186 because it caused
another infinite loop, which is fixed now and a test added.
Otherwise, running e.g.
nix-instantiate --eval -E --strict 'builtins.replaceStrings [""] ["X"] "abc"'
would just hang in an infinite loop.
Found by afl-fuzz.