linux-kernel - Re: [PATCH] ipv4: tcp_input: fix stack out of bounds when parsing TCP options.

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Date:   Thu, 30 May 2019 12:33:05 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     92siuyang@...il.com
Cc:     edumazet@...gle.com, kuznet@....inr.ac.ru, yoshfuji@...ux-ipv6.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ipv4: tcp_input: fix stack out of bounds when parsing
 TCP options.

From: Young Xiao <92siuyang@...il.com>
Date: Wed, 29 May 2019 16:10:59 +0800

> 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@...il.com>

Applied.