From mboxrd@z Thu Jan 1 00:00:00 1970 From: Daniel Borkmann Subject: [PATCH bpf v3 6/9] bpf: restrict unknown scalars of mixed signed bounds for unprivileged Date: Thu, 3 Jan 2019 00:58:32 +0100 Message-ID: <20190102235835.3311-7-daniel@iogearbox.net> References: <20190102235835.3311-1-daniel@iogearbox.net> Cc: jannh@google.com, davem@davemloft.net, jakub.kicinski@netronome.com, netdev@vger.kernel.org, Daniel Borkmann To: ast@kernel.org Return-path: Received: from www62.your-server.de ([213.133.104.62]:42924 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727621AbfABX6r (ORCPT ); Wed, 2 Jan 2019 18:58:47 -0500 In-Reply-To: <20190102235835.3311-1-daniel@iogearbox.net> Sender: netdev-owner@vger.kernel.org List-ID: For unknown scalars of mixed signed bounds, meaning their smin_value is negative and their smax_value is positive, we need to reject arithmetic with pointer to map value. For unprivileged the goal is to mask every map pointer arithmetic and this cannot reliably be done when it is unknown at verification time whether the scalar value is negative or positive. Given this is a corner case, the likelihood of breaking should be very small. Signed-off-by: Daniel Borkmann Acked-by: Alexei Starovoitov --- kernel/bpf/verifier.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/kernel/bpf/verifier.c b/kernel/bpf/verifier.c index 9ac205d..eebbc03 100644 --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -3081,8 +3081,8 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, smin_ptr = ptr_reg->smin_value, smax_ptr = ptr_reg->smax_value; u64 umin_val = off_reg->umin_value, umax_val = off_reg->umax_value, umin_ptr = ptr_reg->umin_value, umax_ptr = ptr_reg->umax_value; + u32 dst = insn->dst_reg, src = insn->src_reg; u8 opcode = BPF_OP(insn->code); - u32 dst = insn->dst_reg; dst_reg = ®s[dst]; @@ -3115,6 +3115,13 @@ static int adjust_ptr_min_max_vals(struct bpf_verifier_env *env, verbose(env, "R%d pointer arithmetic on %s prohibited\n", dst, reg_type_str[ptr_reg->type]); return -EACCES; + case PTR_TO_MAP_VALUE: + if (!env->allow_ptr_leaks && !known && (smin_val < 0) != (smax_val < 0)) { + verbose(env, "R%d has unknown scalar with mixed signed bounds, pointer arithmetic with it prohibited for !root\n", + off_reg == dst_reg ? dst : src); + return -EACCES; + } + /* fall-through */ default: break; } -- 2.9.5