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From:   Young Xiao <92siuyang@gmail.com>
To:     edumazet@google.com, davem@davemloft.net, kuznet@ms2.inr.ac.ru,
        yoshfuji@linux-ipv6.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org
Cc:     Young Xiao <92siuyang@gmail.com>
Subject: [PATCH] ipv4: tcp_input: fix stack out of bounds when parsing TCP options.
Date:   Wed, 29 May 2019 16:10:59 +0800
Message-Id: <1559117459-27353-1-git-send-email-92siuyang@gmail.com>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

The TCP option parsing routines in tcp_parse_options function could
read one byte out of the buffer of the TCP options.

1         while (length > 0) {
2                 int opcode = *ptr++;
3                 int opsize;
4
5                 switch (opcode) {
6                 case TCPOPT_EOL:
7                         return;
8                 case TCPOPT_NOP:        /* Ref: RFC 793 section 3.1 */
9                         length--;
10                        continue;
11                default:
12                        opsize = *ptr++; //out of bound access

If length = 1, then there is an access in line2.
And another access is occurred in line 12.
This would lead to out-of-bound access.

Therefore, in the patch we check that the available data length is
larger enough to pase both TCP option code and size.

Signed-off-by: Young Xiao <92siuyang@gmail.com>
---
 net/ipv4/tcp_input.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 20f6fac..9775825 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -3791,6 +3791,8 @@ void tcp_parse_options(const struct net *net,
 			length--;
 			continue;
 		default:
+			if (length < 2)
+				return;
 			opsize = *ptr++;
 			if (opsize < 2) /* "silly options" */
 				return;
-- 
2.7.4