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helpers.c: Fix undefined behavior in strndup()

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Using strlen() or strdup() inside strndup() is problematic: if the
input string is not null-terminated, these functions can read past the
end of the buffer, which triggers undefined behavior. Rewrite the
function to never read past the provided `maxlen` bound.

Change-Id: Id34127024085879228626fbad59af03268ec5255
Signed-off-by: Xiang Wang <merle@hardenedliux.org>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/49741
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-by: Edward O'Callaghan <quasisec@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-on: https://review.coreboot.org/c/flashrom/+/67870
Reviewed-by: Felix Singer <felixsinger@posteo.net>
This commit is contained in:
Xiang Wang 2021-01-20 17:31:19 +08:00 committed by Felix Singer
parent b822ce85aa
commit 5feb8cdb6f
1 changed files with 9 additions and 8 deletions
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17
helpers.c
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@ -106,15 +106,16 @@ char* strtok_r(char *str, const char *delim, char **nextp)
/* strndup is a POSIX function not present in MinGW */ /* strndup is a POSIX function not present in MinGW */
char *strndup(const char *src, size_t maxlen) char *strndup(const char *src, size_t maxlen)
{ {
if (strlen(src) > maxlen) { char *retbuf;
char *retbuf; size_t len;
if ((retbuf = malloc(1 + maxlen)) != NULL) { for (len = 0; len < maxlen; len++)
memcpy(retbuf, src, maxlen); if (src[len] == '\0')
retbuf[maxlen] = '\0'; break;
} if ((retbuf = malloc(1 + len)) != NULL) {
return retbuf; memcpy(retbuf, src, len);
retbuf[len] = '\0';
} }
return strdup(src); return retbuf;
} }
#endif #endif