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| author | Guy Harris <guy@alum.mit.edu> | 2018-10-26 13:14:37 -0700 |
|---|---|---|
| committer | Guy Harris <guy@alum.mit.edu> | 2018-10-26 13:14:37 -0700 |
| commit | 52a246fb5291e97ba97bc07fc66e0d598484e471 (patch) | |
| tree | 627678444f24b3b6e1eb229d673333959e1707ec /bpf_filter.c | |
| parent | cd512217e570f796ef3e3a7ad67c66d78c83c2dc (diff) | |
| download | libpcap-52a246fb5291e97ba97bc07fc66e0d598484e471.tar.gz | |
Handle negation in a way that doesn't upset compilers or UBSan.
Most BPF arithmetic is unsigned, but negation can't be unsigned;
respecify it as subtracting the value from 0U, so that 1) we don't get
compiler warnings about negating an unsigned value and 2) don't get
UBSan warnings about the result of negating 0x80000000 being undefined.
Credit to OSS-Fuzz for finding these issues.
Diffstat (limited to 'bpf_filter.c')
| -rw-r--r-- | bpf_filter.c | 9 |
1 files changed, 6 insertions, 3 deletions
diff --git a/bpf_filter.c b/bpf_filter.c index b19b25d1..c41d0341 100644 --- a/bpf_filter.c +++ b/bpf_filter.c @@ -358,10 +358,13 @@ pcap_filter_with_aux_data(const struct bpf_insn *pc, const u_char *p, case BPF_ALU|BPF_NEG: /* * Most BPF arithmetic is unsigned, but negation - * can't be unsigned; throw some casts to - * specify what we're trying to do. + * can't be unsigned; respecify it as subtracting + * the accumulator from 0U, so that 1) we don't + * get compiler warnings about negating an unsigned + * value and 2) don't get UBSan warnings about + * the result of negating 0x80000000 being undefined. */ - A = (uint32_t)(-(int32_t)A); + A = (0U - A); continue; case BPF_MISC|BPF_TAX: |