nix-super/src/libexpr/search-path.cc
Sergei Trofimovich b74962c92b src/libexpr/search-path.cc: avoid out-of-bounds read on string_view
Without the change build with `-D_GLIBCXX_ASSERTIONS` exposes testsuite
assertion:

    $ gdb src/libexpr/tests/libnixexpr-tests
    Reading symbols from src/libexpr/tests/libnixexpr-tests...
    (gdb) break __glibcxx_assert_fail
    (gdb) run
    (gdb) bt
    in std::__glibcxx_assert_fail(char const*, int, char const*, char const*)@plt () from /mnt/archive/big/git/nix/src/libexpr/libnixexpr.so
    in std::basic_string_view<char, std::char_traits<char> >::operator[] (this=0x7fffffff56c0, __pos=4)
        at /nix/store/r74fw2j8rx5idb0w8s1s6ynwwgs0qmh9-gcc-14.0.0/include/c++/14.0.0/string_view:258
    in nix::SearchPath::Prefix::suffixIfPotentialMatch (this=0x7fffffff5780, path=...) at src/libexpr/search-path.cc:15
    in nix::SearchPathElem_suffixIfPotentialMatch_partialPrefix_Test::TestBody (this=0x555555a17540) at src/libexpr/tests/search-path.cc:62

As string sizes are usigned types `(a - b) > 0` effectively means
`a != b`. While the intention should be `a > b`.

The change fixes test suite pass.
2023-08-14 22:07:37 +01:00

56 lines
1.3 KiB
C++

#include "search-path.hh"
#include "util.hh"
namespace nix {
std::optional<std::string_view> SearchPath::Prefix::suffixIfPotentialMatch(
std::string_view path) const
{
auto n = s.size();
/* Non-empty prefix and suffix must be separated by a /, or the
prefix is not a valid path prefix. */
bool needSeparator = n > 0 && n < path.size();
if (needSeparator && path[n] != '/') {
return std::nullopt;
}
/* Prefix must be prefix of this path. */
if (path.compare(0, n, s) != 0) {
return std::nullopt;
}
/* Skip next path separator. */
return {
path.substr(needSeparator ? n + 1 : n)
};
}
SearchPath::Elem SearchPath::Elem::parse(std::string_view rawElem)
{
size_t pos = rawElem.find('=');
return SearchPath::Elem {
.prefix = Prefix {
.s = pos == std::string::npos
? std::string { "" }
: std::string { rawElem.substr(0, pos) },
},
.path = Path {
.s = std::string { rawElem.substr(pos + 1) },
},
};
}
SearchPath parseSearchPath(const Strings & rawElems)
{
SearchPath res;
for (auto & rawElem : rawElems)
res.elements.emplace_back(SearchPath::Elem::parse(rawElem));
return res;
}
}