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golomb: always check for invalid UE golomb codes in get_ue_golomb

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Also correct the check to reject log < 7, because UPDATE_CACHE only
guarantees 25 meaningful bits.

This fixes undefined behavior:
runtime error: shift exponent is negative

Testing with START/STOP timers in get_ue_golomb, one for the first
branch (A) and one for the second (B), shows that there is practically no
slowdown, e.g. for the cavs decoder:

With the check in the B branch:
    629 decicycles in get_ue_golomb B, 4194260 runs,     44 skips
    433 decicycles in get_ue_golomb A,268434102 runs,   1354 skips

Without the check:
    624 decicycles in get_ue_golomb B, 4194273 runs,     31 skips
    433 decicycles in get_ue_golomb A,268434203 runs,   1253 skips

Since the B branch is executed far less often than the A branch, this
change is negligible, even more so for the h264 decoder, where the ratio
B/A is a lot smaller.

Fixes: mozilla bug 1230239
Fixes: fbeb8b2c7c996e9b91c6b1af319d7ebc/asan_heap-oob_195450f_2743_e8856ece4579ea486670be2b236099a0.bit

Found-by: Tyson Smith
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>
This commit is contained in:
Andreas Cadhalpun 2015-12-13 21:02:16 +01:00
parent 1925eaeaa6
commit 22e960ad47
1 changed files with 1 additions and 1 deletions
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2
libavcodec/golomb.h
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@ -68,7 +68,7 @@ static inline int get_ue_golomb(GetBitContext *gb)
int log = 2 * av_log2(buf) - 31;
LAST_SKIP_BITS(re, gb, 32 - log);
CLOSE_READER(re, gb);
if (CONFIG_FTRAPV && log < 0) {
if (log < 7) {
av_log(NULL, AV_LOG_ERROR, "Invalid UE golomb code\n");
return AVERROR_INVALIDDATA;
}