Patch "netfilter: xt_owner: Fix for unsafe access of sk->sk_socket" has been added to the 4.19-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    netfilter: xt_owner: Fix for unsafe access of sk->sk_socket

to the 4.19-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     netfilter-xt_owner-fix-for-unsafe-access-of-sk-sk_so.patch
and it can be found in the queue-4.19 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit a4f6458a9bae3dc5635ec3b90f42483f27c47b74
Author: Phil Sutter <phil@xxxxxx>
Date:   Tue Dec 5 21:58:12 2023 +0100

    netfilter: xt_owner: Fix for unsafe access of sk->sk_socket
    
    [ Upstream commit 7ae836a3d630e146b732fe8ef7d86b243748751f ]
    
    A concurrently running sock_orphan() may NULL the sk_socket pointer in
    between check and deref. Follow other users (like nft_meta.c for
    instance) and acquire sk_callback_lock before dereferencing sk_socket.
    
    Fixes: 0265ab44bacc ("[NETFILTER]: merge ipt_owner/ip6t_owner in xt_owner")
    Reported-by: Jann Horn <jannh@xxxxxxxxxx>
    Signed-off-by: Phil Sutter <phil@xxxxxx>
    Signed-off-by: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/netfilter/xt_owner.c b/net/netfilter/xt_owner.c
index a8784502aca69..0c101b25cacf6 100644
--- a/net/netfilter/xt_owner.c
+++ b/net/netfilter/xt_owner.c
@@ -76,18 +76,23 @@ owner_mt(const struct sk_buff *skb, struct xt_action_param *par)
 		 */
 		return false;
 
-	filp = sk->sk_socket->file;
-	if (filp == NULL)
+	read_lock_bh(&sk->sk_callback_lock);
+	filp = sk->sk_socket ? sk->sk_socket->file : NULL;
+	if (filp == NULL) {
+		read_unlock_bh(&sk->sk_callback_lock);
 		return ((info->match ^ info->invert) &
 		       (XT_OWNER_UID | XT_OWNER_GID)) == 0;
+	}
 
 	if (info->match & XT_OWNER_UID) {
 		kuid_t uid_min = make_kuid(net->user_ns, info->uid_min);
 		kuid_t uid_max = make_kuid(net->user_ns, info->uid_max);
 		if ((uid_gte(filp->f_cred->fsuid, uid_min) &&
 		     uid_lte(filp->f_cred->fsuid, uid_max)) ^
-		    !(info->invert & XT_OWNER_UID))
+		    !(info->invert & XT_OWNER_UID)) {
+			read_unlock_bh(&sk->sk_callback_lock);
 			return false;
+		}
 	}
 
 	if (info->match & XT_OWNER_GID) {
@@ -112,10 +117,13 @@ owner_mt(const struct sk_buff *skb, struct xt_action_param *par)
 			}
 		}
 
-		if (match ^ !(info->invert & XT_OWNER_GID))
+		if (match ^ !(info->invert & XT_OWNER_GID)) {
+			read_unlock_bh(&sk->sk_callback_lock);
 			return false;
+		}
 	}
 
+	read_unlock_bh(&sk->sk_callback_lock);
 	return true;
 }