From: Alexei Starovoitov Subject: [PATCH net] bpf: improve verifier packet range checks Date: Fri, 24 Mar 2017 15:57:33 -0700 Message-ID: <20170324225733.2776121-1-ast@fb.com> Mime-Version: 1.0 Content-Type: text/plain Cc: Daniel Borkmann , Martin KaFai Lau , To: "David S . Miller" Return-path: Received: from mx0b-00082601.pphosted.com ([67.231.153.30]:34187 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753411AbdCXW5g (ORCPT ); Fri, 24 Mar 2017 18:57:36 -0400 Received: from pps.filterd (m0001303.ppops.net [127.0.0.1]) by m0001303.ppops.net (8.16.0.20/8.16.0.20) with SMTP id v2OMvYg3017996 for ; Fri, 24 Mar 2017 15:57:34 -0700 Received: from mail.thefacebook.com ([199.201.64.23]) by m0001303.ppops.net with ESMTP id 29cqswmvfe-2 (version=TLSv1 cipher=ECDHE-RSA-AES256-SHA bits=256 verify=NOT) for ; Fri, 24 Mar 2017 15:57:34 -0700 Received: from facebook.com (2401:db00:11:d082:face:0:5:0) by mx-out.facebook.com (10.103.99.97) with ESMTP id 444d33ca10e511e7b8ea0002c9931860-91bfa9a0 for ; Fri, 24 Mar 2017 15:57:33 -0700 Sender: netdev-owner@vger.kernel.org List-ID: llvm can optimize the 'if (ptr > data_end)' checks to be in the order slightly different than the original C code which will confuse verifier. Like: if (ptr + 16 > data_end) return TC_ACT_SHOT; // may be followed by if (ptr + 14 > data_end) return TC_ACT_SHOT; while llvm can see that 'ptr' is valid for all 16 bytes, the verifier could not. Fix verifier logic to account for such case and add a test. Reported-by: Huapeng Zhou Fixes: 969bf05eb3ce ("bpf: direct packet access") Signed-off-by: Alexei Starovoitov Acked-by: Daniel Borkmann Acked-by: Martin KaFai Lau --- new verifier test is added in the middle of older tests to avoid conflicts with new tests in net-next. kernel/bpf/verifier.c | 5 +++-- tools/testing/selftests/bpf/test_verifier.c | 20 ++++++++++++++++++++ 2 files changed, 23 insertions(+), 2 deletions(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 796b68d00119..5e6202e62265 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -1973,14 +1973,15 @@ static void find_good_pkt_pointers(struct bpf_verifier_state *state, for (i = 0; i < MAX_BPF_REG; i++) if (regs[i].type == PTR_TO_PACKET && regs[i].id == dst_reg->id) - regs[i].range = dst_reg->off; + /* keep the maximum range already checked */ + regs[i].range = max(regs[i].range, dst_reg->off); for (i = 0; i < MAX_BPF_STACK; i += BPF_REG_SIZE) { if (state->stack_slot_type[i] != STACK_SPILL) continue; reg = &state->spilled_regs[i / BPF_REG_SIZE]; if (reg->type == PTR_TO_PACKET && reg->id == dst_reg->id) - reg->range = dst_reg->off; + reg->range = max(reg->range, dst_reg->off); } } diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c index d1555e4240c0..7d761d4cc759 100644 --- a/tools/testing/selftests/bpf/test_verifier.c +++ b/tools/testing/selftests/bpf/test_verifier.c @@ -3418,6 +3418,26 @@ static struct bpf_test tests[] = { .prog_type = BPF_PROG_TYPE_LWT_XMIT, }, { + "overlapping checks for direct packet access", + .insns = { + BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1, + offsetof(struct __sk_buff, data)), + BPF_LDX_MEM(BPF_W, BPF_REG_3, BPF_REG_1, + offsetof(struct __sk_buff, data_end)), + BPF_MOV64_REG(BPF_REG_0, BPF_REG_2), + BPF_ALU64_IMM(BPF_ADD, BPF_REG_0, 8), + BPF_JMP_REG(BPF_JGT, BPF_REG_0, BPF_REG_3, 4), + BPF_MOV64_REG(BPF_REG_1, BPF_REG_2), + BPF_ALU64_IMM(BPF_ADD, BPF_REG_1, 6), + BPF_JMP_REG(BPF_JGT, BPF_REG_1, BPF_REG_3, 1), + BPF_LDX_MEM(BPF_H, BPF_REG_0, BPF_REG_2, 6), + BPF_MOV64_IMM(BPF_REG_0, 0), + BPF_EXIT_INSN(), + }, + .result = ACCEPT, + .prog_type = BPF_PROG_TYPE_LWT_XMIT, + }, + { "invalid access of tc_classid for LWT_IN", .insns = { BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1, -- 2.9.3