From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:41068 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754230AbeA2UOr (ORCPT ); Mon, 29 Jan 2018 15:14:47 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, "ast@kernel.org, stable@vger.kernel.org, Daniel Borkmann" , Alexei Starovoitov , Daniel Borkmann Subject: [PATCH 4.9 66/66] bpf: reject stores into ctx via st and xadd Date: Mon, 29 Jan 2018 13:57:30 +0100 Message-Id: <20180129123843.369270247@linuxfoundation.org> In-Reply-To: <20180129123839.842860149@linuxfoundation.org> References: <20180129123839.842860149@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: stable-owner@vger.kernel.org List-ID: 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Daniel Borkmann [ upstream commit f37a8cb84cce18762e8f86a70bd6a49a66ab964c ] Alexei found that verifier does not reject stores into context via BPF_ST instead of BPF_STX. And while looking at it, we also should not allow XADD variant of BPF_STX. The context rewriter is only assuming either BPF_LDX_MEM- or BPF_STX_MEM-type operations, thus reject anything other than that so that assumptions in the rewriter properly hold. Add test cases as well for BPF selftests. Fixes: d691f9e8d440 ("bpf: allow programs to write to certain skb fields") Reported-by: Alexei Starovoitov Signed-off-by: Daniel Borkmann Signed-off-by: Alexei Starovoitov Signed-off-by: Greg Kroah-Hartman --- kernel/bpf/verifier.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -702,6 +702,13 @@ static bool is_pointer_value(struct bpf_ return __is_pointer_value(env->allow_ptr_leaks, &env->cur_state.regs[regno]); } +static bool is_ctx_reg(struct bpf_verifier_env *env, int regno) +{ + const struct bpf_reg_state *reg = &env->cur_state.regs[regno]; + + return reg->type == PTR_TO_CTX; +} + static int check_ptr_alignment(struct bpf_verifier_env *env, struct bpf_reg_state *reg, int off, int size) { @@ -896,6 +903,12 @@ static int check_xadd(struct bpf_verifie return -EACCES; } + if (is_ctx_reg(env, insn->dst_reg)) { + verbose("BPF_XADD stores into R%d context is not allowed\n", + insn->dst_reg); + return -EACCES; + } + /* check whether atomic_add can read the memory */ err = check_mem_access(env, insn->dst_reg, insn->off, BPF_SIZE(insn->code), BPF_READ, -1); @@ -3012,6 +3025,12 @@ static int do_check(struct bpf_verifier_ if (err) return err; + if (is_ctx_reg(env, insn->dst_reg)) { + verbose("BPF_ST stores into R%d context is not allowed\n", + insn->dst_reg); + return -EACCES; + } + /* check that memory (dst_reg + off) is writeable */ err = check_mem_access(env, insn->dst_reg, insn->off, BPF_SIZE(insn->code), BPF_WRITE,