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src/libexpr/search-path.cc: avoid out-of-bounds read on string_view

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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.

(cherry picked from commit b74962c92b)
This commit is contained in:
Sergei Trofimovich 2023-08-14 22:07:37 +01:00 committed by github-actions[bot]
parent 5568ca5ff1
commit d0dd37b2a6
1 changed files with 1 additions and 1 deletions
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src/libexpr/search-path.cc
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@ -10,7 +10,7 @@ std::optional<std::string_view> SearchPath::Prefix::suffixIfPotentialMatch(
/* Non-empty prefix and suffix must be separated by a /, or the
prefix is not a valid path prefix. */
bool needSeparator = n > 0 && (path.size() - n) > 0;
bool needSeparator = n > 0 && n < path.size();
if (needSeparator && path[n] != '/') {
return std::nullopt;