diff options
| author | Frank Mehnert <frank.mehnert@kernkonzept.com> | 2025-01-07 13:09:50 +0100 |
|---|---|---|
| committer | Waldemar Brodkorb <wbx@openadk.org> | 2025-01-07 13:28:17 +0100 |
| commit | b92057584f09d442f27b9177b12fe6fdf36ddbaf (patch) | |
| tree | 10f251b3ce388177ba027e5121f42003ab98aad5 /libc/string/generic | |
| parent | 1de51fb74b68a94207384021a878c1a3035d2aff (diff) | |
fix possible overflow in pointer arithmetics strnlen()
It is undefined behavior to compare two pointers belonging to different
objects. This includes the case where the addition overflows. Clang-20
seems to follow this rule more eagerly and optimizes away the old test.
Fix the test by performing the addition on uintptr_t values rather than
on on char pointers.
See also https://github.com/llvm/llvm-project/issues/121909.
Signed-off-by: Marcus Haehnel <marcus.haehnel@kernkonzept.com>
Diffstat (limited to 'libc/string/generic')
| -rw-r--r-- | libc/string/generic/strnlen.c | 6 |
1 files changed, 4 insertions, 2 deletions
diff --git a/libc/string/generic/strnlen.c b/libc/string/generic/strnlen.c index 4d4cde84f..82d4122ec 100644 --- a/libc/string/generic/strnlen.c +++ b/libc/string/generic/strnlen.c @@ -29,15 +29,17 @@ '\0' terminator is found in that many characters, return MAXLEN. */ size_t strnlen (const char *str, size_t maxlen) { - const char *char_ptr, *end_ptr = str + maxlen; + const char *char_ptr, *end_ptr; const unsigned long int *longword_ptr; unsigned long int longword, himagic, lomagic; if (maxlen == 0) return 0; - if (__builtin_expect (end_ptr < str, 0)) + if (__builtin_expect ((uintptr_t)str + maxlen < (uintptr_t)str, 0)) end_ptr = (const char *) ~0UL; + else + end_ptr = str + maxlen; /* Handle the first few characters by reading one character at a time. Do this until CHAR_PTR is aligned on a longword boundary. */ |