netdev - Re: [Security] [PATCH] sctp: add verification checks to SCTP_AUTH

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Date:	Mon, 25 Aug 2008 18:19:48 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Eugene Teo <eteo@...hat.com>
cc:	Vlad Yasevich <vladislav.yasevich@...com>, netdev@...r.kernel.org,
	linux-sctp@...r.kernel.org, security@...nel.org,
	davem@...emloft.net
Subject: Re: [Security] [PATCH] sctp: add verification checks to SCTP_AUTH_KEY
 option

On Tue, 26 Aug 2008, Eugene Teo wrote:
>
> > @@ -80,6 +80,10 @@ static struct sctp_auth_bytes *sctp_auth_create_key(__u32 key_len, gfp_t gfp)
> 
> This should be __u16 key_len.

Hmm? If it fits in a u16, then there is no worry about overflow.

> >  	struct sctp_auth_bytes *key;
> >  
> > +	/* Verify that we are not going to overflow INT_MAX */
> > +	if ((INT_MAX - key_len) < sizeof(struct sctp_auth_bytes))
> > +		return NULL;
> 
> Shouldn't this be UINT_MAX? But then if you are going to change
> sctp_auth_create_key() to accept __u16 key_len, then it should be
> USHORT_MAX.

If it's ushort, then it shouldn't need any test at all from an overflow 
standpoint. The addition simply can't overflow, since it's always done in 
"size_t" due to the sizeof.

But if it can overflow, I actually think it makes more sense to test for 
something smaller than the "exact" overflow. A key can't reasonably be all 
that long _anyway_, so it's probably better to test for something _much_ 
smaller.

		Linus
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