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| author | Rich Felker <dalias@aerifal.cx> | 2018-09-23 00:03:08 -0400 |
|---|---|---|
| committer | Rich Felker <dalias@aerifal.cx> | 2018-09-23 00:03:08 -0400 |
| commit | debadaa238e90fce897b467a9efefcbbc0155d06 (patch) | |
| tree | 36922273f94c2bba55e05f09ac4997ace0522017 /src/string/memmove.c | |
| parent | c50985d5c8e316c5c464f352e79eeebfed1121a9 (diff) | |
| download | musl-debadaa238e90fce897b467a9efefcbbc0155d06.tar.gz musl-debadaa238e90fce897b467a9efefcbbc0155d06.tar.xz musl-debadaa238e90fce897b467a9efefcbbc0155d06.zip | |
fix undefined pointer comparison in memmove
the comparison must take place in the address space model as an integer type, since comparing pointers that are not pointing into the same array is undefined. the subsequent d<s comparison however is valid, because it's only reached in the case where the source and dest overlap, in which case they are necessarily pointing to parts of the same array. to make the comparison, use an unsigned range check for dist(s,d)>=n, algebraically !(-n<s-d<n). subtracting n yields !(-2*n<s-d-n<0), which mapped into unsigned modular arithmetic is !(-2*n<s-d-n) or rather -2*n>=s-d-n.
Diffstat (limited to 'src/string/memmove.c')
| -rw-r--r-- | src/string/memmove.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/src/string/memmove.c b/src/string/memmove.c index 27f670e1..f225bb30 100644 --- a/src/string/memmove.c +++ b/src/string/memmove.c @@ -10,7 +10,7 @@ void *memmove(void *dest, const void *src, size_t n) const char *s = src; if (d==s) return d; - if (s+n <= d || d+n <= s) return memcpy(d, s, n); + if ((uintptr_t)s-(uintptr_t)d-n <= -2*n) return memcpy(d, s, n); if (d<s) { if ((uintptr_t)s % WS == (uintptr_t)d % WS) { |