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Date:	Tue, 26 Aug 2008 08:59:13 +0800
From:	Eugene Teo <eteo@...hat.com>
To:	Vlad Yasevich <vladislav.yasevich@...com>
CC:	davem@...emloft.net, netdev@...r.kernel.org,
	linux-sctp@...r.kernel.org, security@...nel.org
Subject: Re: [PATCH] sctp: add verification checks to SCTP_AUTH_KEY option

Vlad Yasevich wrote:
> The structure used for SCTP_AUTH_KEY option contains a
> length that needs to be verfied to prevent buffer overflow
> conditions.  Spoted by Eugene Teo <eteo@...hat.com>.
> 
> Signed-off-by: Vlad Yasevich <vladislav.yasevich@...com>
> ---
>  net/sctp/auth.c   |    4 ++++
>  net/sctp/socket.c |    5 +++++
>  2 files changed, 9 insertions(+), 0 deletions(-)
> 
> diff --git a/net/sctp/auth.c b/net/sctp/auth.c
> index 675a5c3..1fcb4cf 100644
> --- a/net/sctp/auth.c
> +++ b/net/sctp/auth.c
> @@ -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.

>  {
>  	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.

>  	/* Allocate the shared key */
>  	key = kmalloc(sizeof(struct sctp_auth_bytes) + key_len, gfp);
>  	if (!key)
> diff --git a/net/sctp/socket.c b/net/sctp/socket.c
> index bb5c9ef..afa952e 100644
> --- a/net/sctp/socket.c
> +++ b/net/sctp/socket.c
> @@ -3144,6 +3144,11 @@ static int sctp_setsockopt_auth_key(struct sock *sk,
>  		goto out;
>  	}
>  
> +	if (authkey->sca_keylength > optlen) {
> +		ret = -EINVAL;
> +		goto out;

Is there a better upper bound check?

>  	asoc = sctp_id2assoc(sk, authkey->sca_assoc_id);
>  	if (!asoc && authkey->sca_assoc_id && sctp_style(sk, UDP)) {
>  		ret = -EINVAL;

Thanks,
Eugene
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