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

["Ahmed S. Darwish" <darwish.07@gmail.com>]

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@gmail.com>
---
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.