netdev - Re: [PATCH] sctp: integer overflow in sctp_auth_create

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Date:	Tue, 29 Nov 2011 02:33:50 -0500
From:	Xi Wang <xi.wang@...il.com>
To:	Vladislav Yasevich <vladislav.yasevich@...com>
Cc:	linux-kernel@...r.kernel.org, Sridhar Samudrala <sri@...ibm.com>,
	"David S. Miller" <davem@...emloft.net>,
	linux-sctp@...r.kernel.org, netdev@...r.kernel.org,
	security@...nel.org
Subject: Re: [PATCH] sctp: integer overflow in sctp_auth_create_key()

I agree that this is not a security issue if key_len can never get large.

So how about just removing the overflow check at all?

- xi

On Nov 28, 2011, at 10:45 AM, Vladislav Yasevich wrote:
> 
> Hmm.  Yes, this is a more correct check.
> 
> Acked-by: Vlad Yasevich <vladislav.yasevich@...com>
> 
> 
> However, I don't think this is a security issue.  As I've written before, this function is
> called from 2 places:
> 
>  1) setsockopt() code path
> 
>  2) sctp_auth_asoc_set_secret() code path
> 
> In case (1), sca_keylength is never going to exceed 65535 since it's
> bounded by a u16 from the user api.  As such, The integer promotion will
> not impact anything and the malloc() will never overflow.
> 
> In case (2), sca_keylength is computed based on the key the user provided
> (MAX_USHORT) and the combination of protocol negotiated data where that
> combination has a max size of 3 * MAX_USHORT (see sctp_auth_make_key_vector()).
> So, even this case, our maximum key length can be 4* MAX_USHORT which still
> will always be below MAX_INT and will not overflow.
> 
> So, I don't think there is big security consideration here, just a bad
> check that just happens to always work.
> 
> -vlad

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