linux-kernel - Re: [PATCH - BUGFIX] Smack: Check for 'struct socket' with NULL sk

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Date:	Tue, 12 Feb 2008 16:35:14 -0800 (PST)
From:	Casey Schaufler <casey@...aufler-ca.com>
To:	"Ahmed S. Darwish" <darwish.07@...il.com>,
	Joerg Platte <jplatte@...sa.net>
Cc:	linux-kernel@...r.kernel.org, casey@...aufler-ca.com
Subject: Re: [PATCH - BUGFIX] Smack: Check for 'struct socket' with NULL sk


--- "Ahmed S. Darwish" <darwish.07@...il.com> wrote:

> On Mon, Feb 11, 2008 at 07:26:02PM +0100, Joerg Platte wrote:
> > Hi,
> > 
> > when booting linux 2.6.25-rc1 I get the following error:
> > 
> > BUG: unable to handle kernel NULL pointer dereference at 00000138
> > IP: [<c01aa59e>] smack_netlabel+0x13/0xc8
> > *pde = 00000000
> > Oops: 0000 [#1] PREEMPT
> > Modules linked in: nfsd 
> [...]
> > Call Trace:
> >  [<c01aacf8>] ? new_inode_smack+0x39/0x3f
> >  [<c01aad52>] ? smack_inode_alloc_security+0x16/0x27
> >  [<c01a7510>] ? security_inode_alloc+0x19/0x1b
> >  [<c01aa665>] ? smack_socket_post_create+0x12/0x18
> >  [<c01a7a06>] ? security_socket_post_create+0x16/0x1b
> >  [<c02116ce>] ? sock_create_lite+0x44/0x64
> >  [<c0211712>] ? kernel_accept+0x24/0x5f
> 
> Hi Joerg,
> 
> There's a small problem with smack and NFS. A similar report was also
> sent here: http://lkml.org/lkml/2007/10/27/85
> 
> Could you please check below patch ? I think it should fix your problem.
> 
> I've also added similar checks in inode_{get/set}security(). Cheating
> from SELinux post_create_socket(), it does the same. Casey, Thoughts ?
> 
> Signed-off-by: Ahmed S. Darwish <darwish.07@...il.com>
Acked-by: Casey Schaufler <casey@...uafler-ca.com>

This looks like the right sort of thing to do. I would like
to see it in. If you would like Ahmed, please submit with my
Acknowlegement. Thank you for the work on this.

> ---
> diff --git a/security/smack/smack_lsm.c b/security/smack/smack_lsm.c
> index 1c11e42..eb04278 100644
> --- a/security/smack/smack_lsm.c
> +++ b/security/smack/smack_lsm.c
> @@ -701,7 +701,7 @@ static int smack_inode_getsecurity(const struct inode
> *inode,
>  		return -EOPNOTSUPP;
>  
>  	sock = SOCKET_I(ip);
> -	if (sock == NULL)
> +	if (sock == NULL || sock->sk == NULL)
>  		return -EOPNOTSUPP;
>  
>  	ssp = sock->sk->sk_security;
> @@ -1280,10 +1280,12 @@ static void smack_to_secattr(char *smack, struct
> netlbl_lsm_secattr *nlsp)
>   */
>  static int smack_netlabel(struct sock *sk)
>  {
> -	struct socket_smack *ssp = sk->sk_security;
> +	struct socket_smack *ssp;
>  	struct netlbl_lsm_secattr secattr;
>  	int rc = 0;
>  
> +	BUG_ON(sk == NULL);
> +	ssp = sk->sk_security;
>  	netlbl_secattr_init(&secattr);
>  	smack_to_secattr(ssp->smk_out, &secattr);
>  	if (secattr.flags != NETLBL_SECATTR_NONE)
> @@ -1331,7 +1333,7 @@ static int smack_inode_setsecurity(struct inode *inode,
> const char *name,
>  		return -EOPNOTSUPP;
>  
>  	sock = SOCKET_I(inode);
> -	if (sock == NULL)
> +	if (sock == NULL || sock->sk == NULL)
>  		return -EOPNOTSUPP;
>  
>  	ssp = sock->sk->sk_security;
> @@ -1362,7 +1364,7 @@ static int smack_inode_setsecurity(struct inode *inode,
> const char *name,
>  static int smack_socket_post_create(struct socket *sock, int family,
>  				    int type, int protocol, int kern)
>  {
> -	if (family != PF_INET)
> +	if (family != PF_INET || sock->sk == NULL)
>  		return 0;
>  	/*
>  	 * Set the outbound netlbl.
> --
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> 
> 
> 


Casey Schaufler
casey@...aufler-ca.com
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