linux-kernel - Re: [PATCH] net: sctp, forbid negative length

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Date:   Sun, 23 Oct 2016 17:44:05 -0400 (EDT)
From:   David Miller <davem@...emloft.net>
To:     jslaby@...e.cz
Cc:     vyasevich@...il.com, linux-kernel@...r.kernel.org,
        nhorman@...driver.com, linux-sctp@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH] net: sctp, forbid negative length

From: Jiri Slaby <jslaby@...e.cz>
Date: Fri, 21 Oct 2016 14:13:24 +0200

> Most of getsockopt handlers in net/sctp/socket.c check len against
> sizeof some structure like:
>         if (len < sizeof(int))
>                 return -EINVAL;
> 
> On the first look, the check seems to be correct. But since len is int
> and sizeof returns size_t, int gets promoted to unsigned size_t too. So
> the test returns false for negative lengths. Yes, (-1 < sizeof(long)) is
> false.
> 
> Fix this in sctp by explicitly checking len < 0 before any getsockopt
> handler is called.
> 
> Note that sctp_getsockopt_events already handled the negative case.
> Since we added the < 0 check elsewhere, this one can be removed.
> 
> If not checked, this is the result:
...
> Signed-off-by: Jiri Slaby <jslaby@...e.cz>

Applied and queued up for -stable, thanks.