From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.linuxfoundation.org ([140.211.169.12]:42916 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751322AbdGRIds (ORCPT ); Tue, 18 Jul 2017 04:33:48 -0400 Subject: Patch "bpf: prevent leaking pointer via xadd on unpriviledged" has been added to the 4.4-stable tree To: daniel@iogearbox.net, ast@kernel.org, davem@davemloft.net, ecree@solarflare.com, gregkh@linuxfoundation.org, kafai@fb.com Cc: , From: Date: Tue, 18 Jul 2017 10:33:42 +0200 Message-ID: <150036682291229@kroah.com> MIME-Version: 1.0 Content-Type: text/plain; charset=ANSI_X3.4-1968 Content-Transfer-Encoding: 8bit Sender: stable-owner@vger.kernel.org List-ID: This is a note to let you know that I've just added the patch titled bpf: prevent leaking pointer via xadd on unpriviledged to the 4.4-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: bpf-prevent-leaking-pointer-via-xadd-on-unpriviledged.patch and it can be found in the queue-4.4 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let know about it. >>From 6bdf6abc56b53103324dfd270a86580306e1a232 Mon Sep 17 00:00:00 2001 From: Daniel Borkmann Date: Thu, 29 Jun 2017 03:04:59 +0200 Subject: bpf: prevent leaking pointer via xadd on unpriviledged From: Daniel Borkmann commit 6bdf6abc56b53103324dfd270a86580306e1a232 upstream. Leaking kernel addresses on unpriviledged is generally disallowed, for example, verifier rejects the following: 0: (b7) r0 = 0 1: (18) r2 = 0xffff897e82304400 3: (7b) *(u64 *)(r1 +48) = r2 R2 leaks addr into ctx Doing pointer arithmetic on them is also forbidden, so that they don't turn into unknown value and then get leaked out. However, there's xadd as a special case, where we don't check the src reg for being a pointer register, e.g. the following will pass: 0: (b7) r0 = 0 1: (7b) *(u64 *)(r1 +48) = r0 2: (18) r2 = 0xffff897e82304400 ; map 4: (db) lock *(u64 *)(r1 +48) += r2 5: (95) exit We could store the pointer into skb->cb, loose the type context, and then read it out from there again to leak it eventually out of a map value. Or more easily in a different variant, too: 0: (bf) r6 = r1 1: (7a) *(u64 *)(r10 -8) = 0 2: (bf) r2 = r10 3: (07) r2 += -8 4: (18) r1 = 0x0 6: (85) call bpf_map_lookup_elem#1 7: (15) if r0 == 0x0 goto pc+3 R0=map_value(ks=8,vs=8,id=0),min_value=0,max_value=0 R6=ctx R10=fp 8: (b7) r3 = 0 9: (7b) *(u64 *)(r0 +0) = r3 10: (db) lock *(u64 *)(r0 +0) += r6 11: (b7) r0 = 0 12: (95) exit from 7 to 11: R0=inv,min_value=0,max_value=0 R6=ctx R10=fp 11: (b7) r0 = 0 12: (95) exit Prevent this by checking xadd src reg for pointer types. Also add a couple of test cases related to this. Fixes: 1be7f75d1668 ("bpf: enable non-root eBPF programs") Fixes: 17a5267067f3 ("bpf: verifier (add verifier core)") Signed-off-by: Daniel Borkmann Acked-by: Alexei Starovoitov Acked-by: Martin KaFai Lau Acked-by: Edward Cree Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- kernel/bpf/verifier.c | 5 +++++ 1 file changed, 5 insertions(+) --- a/kernel/bpf/verifier.c +++ b/kernel/bpf/verifier.c @@ -754,6 +754,11 @@ static int check_xadd(struct verifier_en if (err) return err; + if (is_pointer_value(env, insn->src_reg)) { + verbose("R%d leaks addr into mem\n", insn->src_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); Patches currently in stable-queue which might be from daniel@iogearbox.net are queue-4.4/bpf-prevent-leaking-pointer-via-xadd-on-unpriviledged.patch