From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753190AbdH1I5e (ORCPT ); Mon, 28 Aug 2017 04:57:34 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:33892 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752956AbdH1IK4 (ORCPT ); Mon, 28 Aug 2017 04:10:56 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Daniel Borkmann , Josef Bacik , Alexei Starovoitov , "David S. Miller" Subject: [PATCH 4.9 24/84] bpf, verifier: fix alu ops against map_value{, _adj} register types Date: Mon, 28 Aug 2017 10:04:49 +0200 Message-Id: <20170828080530.489795915@linuxfoundation.org> X-Mailer: git-send-email 2.14.1 In-Reply-To: <20170828080529.526391781@linuxfoundation.org> References: <20170828080529.526391781@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Daniel Borkmann [ Upstream commit fce366a9dd0ddc47e7ce05611c266e8574a45116 ] While looking into map_value_adj, I noticed that alu operations directly on the map_value() resp. map_value_adj() register (any alu operation on a map_value() register will turn it into a map_value_adj() typed register) are not sufficiently protected against some of the operations. Two non-exhaustive examples are provided that the verifier needs to reject: i) BPF_AND on r0 (map_value_adj): 0: (bf) r2 = r10 1: (07) r2 += -8 2: (7a) *(u64 *)(r2 +0) = 0 3: (18) r1 = 0xbf842a00 5: (85) call bpf_map_lookup_elem#1 6: (15) if r0 == 0x0 goto pc+2 R0=map_value(ks=8,vs=48,id=0),min_value=0,max_value=0 R10=fp 7: (57) r0 &= 8 8: (7a) *(u64 *)(r0 +0) = 22 R0=map_value_adj(ks=8,vs=48,id=0),min_value=0,max_value=8 R10=fp 9: (95) exit from 6 to 9: R0=inv,min_value=0,max_value=0 R10=fp 9: (95) exit processed 10 insns ii) BPF_ADD in 32 bit mode on r0 (map_value_adj): 0: (bf) r2 = r10 1: (07) r2 += -8 2: (7a) *(u64 *)(r2 +0) = 0 3: (18) r1 = 0xc24eee00 5: (85) call bpf_map_lookup_elem#1 6: (15) if r0 == 0x0 goto pc+2 R0=map_value(ks=8,vs=48,id=0),min_value=0,max_value=0 R10=fp 7: (04) (u32) r0 += (u32) 0 8: (7a) *(u64 *)(r0 +0) = 22 R0=map_value_adj(ks=8,vs=48,id=0),min_value=0,max_value=0 R10=fp 9: (95) exit from 6 to 9: R0=inv,min_value=0,max_value=0 R10=fp 9: (95) exit processed 10 insns Issue is, while min_value / max_value boundaries for the access are adjusted appropriately, we change the pointer value in a way that cannot be sufficiently tracked anymore from its origin. Operations like BPF_{AND,OR,DIV,MUL,etc} on a destination register that is PTR_TO_MAP_VALUE{,_ADJ} was probably unintended, in fact, all the test cases coming with 484611357c19 ("bpf: allow access into map value arrays") perform BPF_ADD only on the destination register that is PTR_TO_MAP_VALUE_ADJ. Only for UNKNOWN_VALUE register types such operations make sense, f.e. with unknown memory content fetched initially from a constant offset from the map value memory into a register. That register is then later tested against lower / upper bounds, so that the verifier can then do the tracking of min_value / max_value, and properly check once that UNKNOWN_VALUE register is added to the destination register with type PTR_TO_MAP_VALUE{,_ADJ}. This is also what the original use-case is solving. Note, tracking on what is being added is done through adjust_reg_min_max_vals() and later access to the map value enforced with these boundaries and the given offset from the insn through check_map_access_adj(). Tests will fail for non-root environment due to prohibited pointer arithmetic, in particular in check_alu_op(), we bail out on the is_pointer_value() check on the dst_reg (which is false in root case as we allow for pointer arithmetic via env->allow_ptr_leaks). Similarly to PTR_TO_PACKET, one way to fix it is to restrict the allowed operations on PTR_TO_MAP_VALUE{,_ADJ} registers to 64 bit mode BPF_ADD. The test_verifier suite runs fine after the patch and it also rejects mentioned test cases. Fixes: 484611357c19 ("bpf: allow access into map value arrays") Signed-off-by: Daniel Borkmann Reviewed-by: Josef Bacik Acked-by: Alexei Starovoitov Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- kernel/bpf/verifier.c | 1 + 1 file changed, 1 insertion(+) --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -1870,6 +1870,7 @@ static int check_alu_op(struct bpf_verif * register as unknown. */ if (env->allow_ptr_leaks && + BPF_CLASS(insn->code) == BPF_ALU64 && opcode == BPF_ADD && (dst_reg->type == PTR_TO_MAP_VALUE || dst_reg->type == PTR_TO_MAP_VALUE_ADJ)) dst_reg->type = PTR_TO_MAP_VALUE_ADJ;