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Date: Wed, 14 Oct 2020 22:46:47 -0700 From: Yonghong Song <yhs@...com> To: Alexei Starovoitov <alexei.starovoitov@...il.com>, <davem@...emloft.net> CC: <daniel@...earbox.net>, <john.fastabend@...il.com>, <netdev@...r.kernel.org>, <bpf@...r.kernel.org>, <kernel-team@...com> Subject: Re: [PATCH bpf-next] bpf: Fix register equivalence tracking. On 10/14/20 10:56 AM, Alexei Starovoitov wrote: > From: Alexei Starovoitov <ast@...nel.org> > > The 64-bit JEQ/JNE handling in reg_set_min_max() was clearing reg->id in either > true or false branch. In the case 'if (reg->id)' check was done on the other > branch the counter part register would have reg->id == 0 when called into > find_equal_scalars(). In such case the helper would incorrectly identify other > registers with id == 0 as equivalent and propagate the state incorrectly. > Fix it by preserving ID across reg_set_min_max(). > In other words any kind of comparison operator on the scalar register > should preserve its ID to recognize: > r1 = r2 > if (r1 == 20) { > #1 here both r1 and r2 == 20 > } else if (r2 < 20) { > #2 here both r1 and r2 < 20 > } > > The patch is addressing #1 case. The #2 was working correctly already. > > Fixes: 75748837b7e5 ("bpf: Propagate scalar ranges through register assignments.") > Signed-off-by: Alexei Starovoitov <ast@...nel.org> This fixed an issue appeared in our production system where packets may be incorrectly dropped. Test-by: Yonghong Song <yhs@...com>
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