linux-kernel - [PATCH AUTOSEL 4.18 28/76] bpf: fix shift upon scatterlist ring wrap-around in bpf_msg_pull

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite for Android: free password hash cracker in your pocket

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20180924144751.164410-28-alexander.levin@microsoft.com>
Date:   Mon, 24 Sep 2018 14:48:18 +0000
From:   Sasha Levin <Alexander.Levin@...rosoft.com>
To:     "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Sasha Levin <Alexander.Levin@...rosoft.com>
Subject: [PATCH AUTOSEL 4.18 28/76] bpf: fix shift upon scatterlist ring
 wrap-around in bpf_msg_pull_data

From: Daniel Borkmann <daniel@...earbox.net>

[ Upstream commit 2e43f95dd8ee62bc8bf57f2afac37fbd70c8d565 ]

If first_sg and last_sg wraps around in the scatterlist ring, then we
need to account for that in the shift as well. E.g. crafting such msgs
where this is the case leads to a hang as shift becomes negative. E.g.
consider the following scenario:

  first_sg := 14     |=>    shift := -12     msg->sg_start := 10
  last_sg  :=  3     |                       msg->sg_end   :=  5

round  1:  i := 15, move_from :=   3, sg[15] := sg[  3]
round  2:  i :=  0, move_from := -12, sg[ 0] := sg[-12]
round  3:  i :=  1, move_from := -11, sg[ 1] := sg[-11]
round  4:  i :=  2, move_from := -10, sg[ 2] := sg[-10]
[...]
round 13:  i := 11, move_from :=  -1, sg[ 2] := sg[ -1]
round 14:  i := 12, move_from :=   0, sg[ 2] := sg[  0]
round 15:  i := 13, move_from :=   1, sg[ 2] := sg[  1]
round 16:  i := 14, move_from :=   2, sg[ 2] := sg[  2]
round 17:  i := 15, move_from :=   3, sg[ 2] := sg[  3]
[...]

This means we will loop forever and never hit the msg->sg_end condition
to break out of the loop. When we see that the ring wraps around, then
the shift should be MAX_SKB_FRAGS - first_sg + last_sg - 1. Meaning,
the remainder slots from the tail of the ring and the head until last_sg
combined.

Fixes: 015632bb30da ("bpf: sk_msg program helper bpf_sk_msg_pull_data")
Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
Acked-by: John Fastabend <john.fastabend@...il.com>
Signed-off-by: Alexei Starovoitov <ast@...nel.org>
Signed-off-by: Sasha Levin <alexander.levin@...rosoft.com>
---
 net/core/filter.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index e713a8791815..cc4d660aafe1 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2360,7 +2360,10 @@ BPF_CALL_4(bpf_msg_pull_data,
 	 * had a single entry though we can just replace it and
 	 * be done. Otherwise walk the ring and shift the entries.
 	 */
-	shift = last_sg - first_sg - 1;
+	WARN_ON_ONCE(last_sg == first_sg);
+	shift = last_sg > first_sg ?
+		last_sg - first_sg - 1 :
+		MAX_SKB_FRAGS - first_sg + last_sg - 1;
 	if (!shift)
 		goto out;
 
-- 
2.17.1