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avutil/avstring: Fix bug and undefined behavior in av_strncasecmp() 

The function in case of n=0 would read more bytes than 0.
The end pointer could be beyond the allocated space, which
is undefined.

Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
This commit is contained in:
Michael Niedermayer 2019-04-16 00:09:38 +02:00
parent 18a567c369
commit 6f0e9a8634
1 changed files with 3 additions and 2 deletions
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5
libavutil/avstring.c
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@ -222,12 +222,13 @@ int av_strcasecmp(const char *a, const char *b)
int av_strncasecmp(const char *a, const char *b, size_t n) int av_strncasecmp(const char *a, const char *b, size_t n)
{ {
const char *end = a + n;
uint8_t c1, c2; uint8_t c1, c2;
if (n <= 0)
return 0;
do { do {
c1 = av_tolower(*a++); c1 = av_tolower(*a++);
c2 = av_tolower(*b++); c2 = av_tolower(*b++);
} while (a < end && c1 && c1 == c2); } while (--n && c1 && c1 == c2);
return c1 - c2; return c1 - c2;
} }