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nmblib: avoid undefined behaviour in handle_name_ptrs()

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If *offset is length - 1, we would read ubuf[(*offset)+1] as the lower
bits of the new *offset. This value is undefined, but because it is
checked against the valid range, there is no way to read further
beyond that one byte.

Credit to oss-fuzz.

BUG: https://bugzilla.samba.org/show_bug.cgi?id=14242
OSS-Fuzz: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=20193

Signed-off-by: Douglas Bagnall <douglas.bagnall@catalyst.net.nz>
Reviewed-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>

Autobuild-User(master): Andrew Bartlett <abartlet@samba.org>
Autobuild-Date(master): Fri Feb  7 10:19:39 UTC 2020 on sn-devel-184
This commit is contained in:
Douglas Bagnall 2020-01-19 15:08:58 +13:00 committed by Andrew Bartlett
parent 91d4e79c27
commit 3bc7acc626
1 changed files with 3 additions and 0 deletions
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3
source3/libsmb/nmblib.c
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@ -160,6 +160,9 @@ static bool handle_name_ptrs(unsigned char *ubuf,int *offset,int length,
if (!*got_pointer)
(*ret) += 2;
(*got_pointer)=True;
if (*offset > length - 2) {
return False;
}
(*offset) = ((ubuf[*offset] & ~0xC0)<<8) | ubuf[(*offset)+1];
if (loop_count++ == 10 ||
(*offset) < 0 || (*offset)>(length-2)) {