linux-kernel - Re: [PATCH net] tcp: don't read out-of-bounds opsize

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Message-Id: <20180423.095249.1008800065389287269.davem@davemloft.net>
Date:   Mon, 23 Apr 2018 09:52:49 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     jannh@...gle.com
Cc:     kuznet@....inr.ac.ru, yoshfuji@...ux-ipv6.org,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] tcp: don't read out-of-bounds opsize

From: Jann Horn <jannh@...gle.com>
Date: Fri, 20 Apr 2018 15:57:30 +0200

> The old code reads the "opsize" variable from out-of-bounds memory (first
> byte behind the segment) if a broken TCP segment ends directly after an
> opcode that is neither EOL nor NOP.
> 
> The result of the read isn't used for anything, so the worst thing that
> could theoretically happen is a pagefault; and since the physmap is usually
> mostly contiguous, even that seems pretty unlikely.
> 
> The following C reproducer triggers the uninitialized read - however, you
> can't actually see anything happen unless you put something like a
> pr_warn() in tcp_parse_md5sig_option() to print the opsize.
 ...
> Fixes: cfb6eeb4c860 ("[TCP]: MD5 Signature Option (RFC2385) support.")
> Signed-off-by: Jann Horn <jannh@...gle.com>

Applied and queued up for -stable, thank you.