From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alexei Starovoitov Subject: [PATCH net] bpf: fix verifier memory corruption Date: Tue, 14 Apr 2015 15:57:13 -0700 Message-ID: <1429052233-8252-1-git-send-email-ast@plumgrid.com> Cc: Daniel Borkmann , Hannes Frederic Sowa , netdev@vger.kernel.org To: "David S. Miller" Return-path: Received: from mail-pd0-f174.google.com ([209.85.192.174]:36243 "EHLO mail-pd0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754179AbbDNW5Y (ORCPT ); Tue, 14 Apr 2015 18:57:24 -0400 Received: by pdea3 with SMTP id a3so28658544pde.3 for ; Tue, 14 Apr 2015 15:57:23 -0700 (PDT) Sender: netdev-owner@vger.kernel.org List-ID: Due to missing bounds check the DAG pass of the BPF verifier can corrupt the memory which can cause random crashes during program loading: [8.449451] BUG: unable to handle kernel paging request at ffffffffffffffff [8.451293] IP: [] kmem_cache_alloc_trace+0x8d/0x2f0 [8.452329] Oops: 0000 [#1] SMP [8.452329] Call Trace: [8.452329] [] bpf_check+0x852/0x2000 [8.452329] [] bpf_prog_load+0x1e4/0x310 [8.452329] [] ? might_fault+0x5f/0xb0 [8.452329] [] SyS_bpf+0x806/0xa30 Fixes: f1bca824dabb ("bpf: add search pruning optimization to verifier") Signed-off-by: Alexei Starovoitov --- Many things need to align for this crash to be seen, yet I managed to hit it. In my case JA was last insn, 't' was 255 and explored_states array had 256 elements. I've double checked other similar paths and all seems clean. kernel/bpf/verifier.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index a28e09c7825d..36508e69e92a 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -1380,7 +1380,8 @@ peek_stack: /* tell verifier to check for equivalent states * after every call and jump */ - env->explored_states[t + 1] = STATE_LIST_MARK; + if (t + 1 < insn_cnt) + env->explored_states[t + 1] = STATE_LIST_MARK; } else { /* conditional jump with two edges */ ret = push_insn(t, t + 1, FALLTHROUGH, env); -- 1.7.9.5