Patch "af_unix: Update unix_sk(sk)->oob_skb under sk_receive_queue lock." has been added to the 6.8-stable tree

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

    af_unix: Update unix_sk(sk)->oob_skb under sk_receive_queue lock.

to the 6.8-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:
     af_unix-update-unix_sk-sk-oob_skb-under-sk_receive_q.patch
and it can be found in the queue-6.8 subdirectory.

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



commit db864b207bedc53319561f570a11ffe206ccdb36
Author: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
Date:   Thu May 16 22:48:35 2024 +0900

    af_unix: Update unix_sk(sk)->oob_skb under sk_receive_queue lock.
    
    [ Upstream commit 9841991a446c87f90f66f4b9fee6fe934c1336a2 ]
    
    Billy Jheng Bing-Jhong reported a race between __unix_gc() and
    queue_oob().
    
    __unix_gc() tries to garbage-collect close()d inflight sockets,
    and then if the socket has MSG_OOB in unix_sk(sk)->oob_skb, GC
    will drop the reference and set NULL to it locklessly.
    
    However, the peer socket still can send MSG_OOB message and
    queue_oob() can update unix_sk(sk)->oob_skb concurrently, leading
    NULL pointer dereference. [0]
    
    To fix the issue, let's update unix_sk(sk)->oob_skb under the
    sk_receive_queue's lock and take it everywhere we touch oob_skb.
    
    Note that we defer kfree_skb() in manage_oob() to silence lockdep
    false-positive (See [1]).
    
    [0]:
    BUG: kernel NULL pointer dereference, address: 0000000000000008
     PF: supervisor write access in kernel mode
     PF: error_code(0x0002) - not-present page
    PGD 8000000009f5e067 P4D 8000000009f5e067 PUD 9f5d067 PMD 0
    Oops: 0002 [#1] PREEMPT SMP PTI
    CPU: 3 PID: 50 Comm: kworker/3:1 Not tainted 6.9.0-rc5-00191-gd091e579b864 #110
    Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014
    Workqueue: events delayed_fput
    RIP: 0010:skb_dequeue (./include/linux/skbuff.h:2386 ./include/linux/skbuff.h:2402 net/core/skbuff.c:3847)
    Code: 39 e3 74 3e 8b 43 10 48 89 ef 83 e8 01 89 43 10 49 8b 44 24 08 49 c7 44 24 08 00 00 00 00 49 8b 14 24 49 c7 04 24 00 00 00 00 <48> 89 42 08 48 89 10 e8 e7 c5 42 00 4c 89 e0 5b 5d 41 5c c3 cc cc
    RSP: 0018:ffffc900001bfd48 EFLAGS: 00000002
    RAX: 0000000000000000 RBX: ffff8880088f5ae8 RCX: 00000000361289f9
    RDX: 0000000000000000 RSI: 0000000000000206 RDI: ffff8880088f5b00
    RBP: ffff8880088f5b00 R08: 0000000000080000 R09: 0000000000000001
    R10: 0000000000000003 R11: 0000000000000001 R12: ffff8880056b6a00
    R13: ffff8880088f5280 R14: 0000000000000001 R15: ffff8880088f5a80
    FS:  0000000000000000(0000) GS:ffff88807dd80000(0000) knlGS:0000000000000000
    CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
    CR2: 0000000000000008 CR3: 0000000006314000 CR4: 00000000007506f0
    PKRU: 55555554
    Call Trace:
     <TASK>
     unix_release_sock (net/unix/af_unix.c:654)
     unix_release (net/unix/af_unix.c:1050)
     __sock_release (net/socket.c:660)
     sock_close (net/socket.c:1423)
     __fput (fs/file_table.c:423)
     delayed_fput (fs/file_table.c:444 (discriminator 3))
     process_one_work (kernel/workqueue.c:3259)
     worker_thread (kernel/workqueue.c:3329 kernel/workqueue.c:3416)
     kthread (kernel/kthread.c:388)
     ret_from_fork (arch/x86/kernel/process.c:153)
     ret_from_fork_asm (arch/x86/entry/entry_64.S:257)
     </TASK>
    Modules linked in:
    CR2: 0000000000000008
    
    Link: https://lore.kernel.org/netdev/a00d3993-c461-43f2-be6d-07259c98509a@xxxxxxx/ [1]
    Fixes: 1279f9d9dec2 ("af_unix: Call kfree_skb() for dead unix_(sk)->oob_skb in GC.")
    Reported-by: Billy Jheng Bing-Jhong <billy@xxxxxxxxxxx>
    Signed-off-by: Kuniyuki Iwashima <kuniyu@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20240516134835.8332-1-kuniyu@xxxxxxxxxx
    Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index eb90a255507ef..6afa6d24818fb 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -2157,13 +2157,15 @@ static int queue_oob(struct socket *sock, struct msghdr *msg, struct sock *other
 	maybe_add_creds(skb, sock, other);
 	skb_get(skb);
 
+	scm_stat_add(other, skb);
+
+	spin_lock(&other->sk_receive_queue.lock);
 	if (ousk->oob_skb)
 		consume_skb(ousk->oob_skb);
-
 	WRITE_ONCE(ousk->oob_skb, skb);
+	__skb_queue_tail(&other->sk_receive_queue, skb);
+	spin_unlock(&other->sk_receive_queue.lock);
 
-	scm_stat_add(other, skb);
-	skb_queue_tail(&other->sk_receive_queue, skb);
 	sk_send_sigurg(other);
 	unix_state_unlock(other);
 	other->sk_data_ready(other);
@@ -2553,8 +2555,10 @@ static int unix_stream_recv_urg(struct unix_stream_read_state *state)
 
 	mutex_lock(&u->iolock);
 	unix_state_lock(sk);
+	spin_lock(&sk->sk_receive_queue.lock);
 
 	if (sock_flag(sk, SOCK_URGINLINE) || !u->oob_skb) {
+		spin_unlock(&sk->sk_receive_queue.lock);
 		unix_state_unlock(sk);
 		mutex_unlock(&u->iolock);
 		return -EINVAL;
@@ -2566,6 +2570,8 @@ static int unix_stream_recv_urg(struct unix_stream_read_state *state)
 		WRITE_ONCE(u->oob_skb, NULL);
 	else
 		skb_get(oob_skb);
+
+	spin_unlock(&sk->sk_receive_queue.lock);
 	unix_state_unlock(sk);
 
 	chunk = state->recv_actor(oob_skb, 0, chunk, state);
@@ -2594,6 +2600,10 @@ static struct sk_buff *manage_oob(struct sk_buff *skb, struct sock *sk,
 		consume_skb(skb);
 		skb = NULL;
 	} else {
+		struct sk_buff *unlinked_skb = NULL;
+
+		spin_lock(&sk->sk_receive_queue.lock);
+
 		if (skb == u->oob_skb) {
 			if (copied) {
 				skb = NULL;
@@ -2605,13 +2615,19 @@ static struct sk_buff *manage_oob(struct sk_buff *skb, struct sock *sk,
 			} else if (flags & MSG_PEEK) {
 				skb = NULL;
 			} else {
-				skb_unlink(skb, &sk->sk_receive_queue);
+				__skb_unlink(skb, &sk->sk_receive_queue);
 				WRITE_ONCE(u->oob_skb, NULL);
-				if (!WARN_ON_ONCE(skb_unref(skb)))
-					kfree_skb(skb);
+				unlinked_skb = skb;
 				skb = skb_peek(&sk->sk_receive_queue);
 			}
 		}
+
+		spin_unlock(&sk->sk_receive_queue.lock);
+
+		if (unlinked_skb) {
+			WARN_ON_ONCE(skb_unref(unlinked_skb));
+			kfree_skb(unlinked_skb);
+		}
 	}
 	return skb;
 }




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