[PATCH v1 bpf] sockmap: Fix use-after-free of sk->sk_socket in sk_psock_verdict_data_ready().

[PATCH v1 bpf] sockmap: Fix use-after-free of sk->sk_socket in sk_psock_verdict_data_ready().

[Kuniyuki Iwashima]

syzbot reported use-after-free of AF_UNIX socket's sk->sk_socket
in sk_psock_verdict_data_ready(). [0]

In unix_stream_sendmsg(), the peer socket's ->sk_data_ready() is
called after dropping its unix_state_lock().

Although the sender socket holds the peer's refcount, it does not
prevent the peer's sock_orphan(), and the peer's sk_socket might
be freed after one RCU grace period.

Let's fetch the peer's sk->sk_socket and sk->sk_socket->ops under
RCU in sk_psock_verdict_data_ready().

[0]:
BUG: KASAN: slab-use-after-free in sk_psock_verdict_data_ready+0xec/0x590 net/core/skmsg.c:1278
Read of size 8 at addr ffff8880594da860 by task syz.4.1842/11013

CPU: 1 UID: 0 PID: 11013 Comm: syz.4.1842 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xba/0x230 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 sk_psock_verdict_data_ready+0xec/0x590 net/core/skmsg.c:1278
 unix_stream_sendmsg+0x8a3/0xe80 net/unix/af_unix.c:2482
 sock_sendmsg_nosec net/socket.c:721 [inline]
 __sock_sendmsg net/socket.c:736 [inline]
 ____sys_sendmsg+0x972/0x9f0 net/socket.c:2585
 ___sys_sendmsg+0x2a5/0x360 net/socket.c:2639
 __sys_sendmsg net/socket.c:2671 [inline]
 __do_sys_sendmsg net/socket.c:2676 [inline]
 __se_sys_sendmsg net/socket.c:2674 [inline]
 __x64_sys_sendmsg+0x1bd/0x2a0 net/socket.c:2674
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7facf899c819
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007facf9827028 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007facf8c15fa0 RCX: 00007facf899c819
RDX: 0000000000000000 RSI: 0000200000000500 RDI: 0000000000000004
RBP: 00007facf8a32c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007facf8c16038 R14: 00007facf8c15fa0 R15: 00007ffd41b01c78
 </TASK>

Allocated by task 11013:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 unpoison_slab_object mm/kasan/common.c:340 [inline]
 __kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:366
 kasan_slab_alloc include/linux/kasan.h:253 [inline]
 slab_post_alloc_hook mm/slub.c:4538 [inline]
 slab_alloc_node mm/slub.c:4866 [inline]
 kmem_cache_alloc_lru_noprof+0x2b8/0x640 mm/slub.c:4885
 sock_alloc_inode+0x28/0xc0 net/socket.c:316
 alloc_inode+0x6a/0x1b0 fs/inode.c:347
 new_inode_pseudo include/linux/fs.h:3003 [inline]
 sock_alloc net/socket.c:631 [inline]
 __sock_create+0x12d/0x9d0 net/socket.c:1562
 sock_create net/socket.c:1656 [inline]
 __sys_socketpair+0x1c4/0x560 net/socket.c:1803
 __do_sys_socketpair net/socket.c:1856 [inline]
 __se_sys_socketpair net/socket.c:1853 [inline]
 __x64_sys_socketpair+0x9b/0xb0 net/socket.c:1853
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 15:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2685 [inline]
 slab_free mm/slub.c:6165 [inline]
 kmem_cache_free+0x187/0x630 mm/slub.c:6295
 rcu_do_batch kernel/rcu/tree.c:2617 [inline]
 rcu_core+0x7cd/0x1070 kernel/rcu/tree.c:2869
 handle_softirqs+0x22a/0x870 kernel/softirq.c:622
 run_ksoftirqd+0x36/0x60 kernel/softirq.c:1063
 smpboot_thread_fn+0x541/0xa50 kernel/smpboot.c:160
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Fixes: c63829182c37 ("af_unix: Implement ->psock_update_sk_prot()")
Reported-by: syzbot+2184232f07e3677fbaef@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/bpf/69cc6b9f.a70a0220.128fd0.004b.GAE@google.com/
Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>
---
 net/core/skmsg.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/net/core/skmsg.c b/net/core/skmsg.c
index 3261793abe83..6187a83bd741 100644
--- a/net/core/skmsg.c
+++ b/net/core/skmsg.c
@@ -1267,17 +1267,20 @@ static int sk_psock_verdict_recv(struct sock *sk, struct sk_buff *skb)
 
 static void sk_psock_verdict_data_ready(struct sock *sk)
 {
-	struct socket *sock = sk->sk_socket;
-	const struct proto_ops *ops;
+	const struct proto_ops *ops = NULL;
+	struct socket *sock;
 	int copied;
 
 	trace_sk_data_ready(sk);
 
-	if (unlikely(!sock))
-		return;
-	ops = READ_ONCE(sock->ops);
+	rcu_read_lock();
+	sock = READ_ONCE(sk->sk_socket);
+	if (likely(sock))
+		ops = READ_ONCE(sock->ops);
+	rcu_read_unlock();
 	if (!ops || !ops->read_skb)
 		return;
+
 	copied = ops->read_skb(sk, sk_psock_verdict_recv);
 	if (copied >= 0) {
 		struct sk_psock *psock;
-- 
2.53.0.1118.gaef5881109-goog

Re: [PATCH v1 bpf] sockmap: Fix use-after-free of sk->sk_socket in sk_psock_verdict_data_ready().

[Jiayuan Chen]

On 4/1/26 8:54 AM, Kuniyuki Iwashima wrote:
> syzbot reported use-after-free of AF_UNIX socket's sk->sk_socket
> in sk_psock_verdict_data_ready(). [0]
>
> In unix_stream_sendmsg(), the peer socket's ->sk_data_ready() is
> called after dropping its unix_state_lock().
>
> Although the sender socket holds the peer's refcount, it does not
> prevent the peer's sock_orphan(), and the peer's sk_socket might
> be freed after one RCU grace period.
>
> Let's fetch the peer's sk->sk_socket and sk->sk_socket->ops under
> RCU in sk_psock_verdict_data_ready().
>
> [0]:
> BUG: KASAN: slab-use-after-free in sk_psock_verdict_data_ready+0xec/0x590 net/core/skmsg.c:1278
> Read of size 8 at addr ffff8880594da860 by task syz.4.1842/11013
>
> CPU: 1 UID: 0 PID: 11013 Comm: syz.4.1842 Not tainted syzkaller #0 PREEMPT(full)
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
> Call Trace:
>   <TASK>
>   dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
>   print_address_description mm/kasan/report.c:378 [inline]
>   print_report+0xba/0x230 mm/kasan/report.c:482
>   kasan_report+0x117/0x150 mm/kasan/report.c:595
>   sk_psock_verdict_data_ready+0xec/0x590 net/core/skmsg.c:1278
>   unix_stream_sendmsg+0x8a3/0xe80 net/unix/af_unix.c:2482
>   sock_sendmsg_nosec net/socket.c:721 [inline]
>   __sock_sendmsg net/socket.c:736 [inline]
>   ____sys_sendmsg+0x972/0x9f0 net/socket.c:2585
>   ___sys_sendmsg+0x2a5/0x360 net/socket.c:2639
>   __sys_sendmsg net/socket.c:2671 [inline]
>   __do_sys_sendmsg net/socket.c:2676 [inline]
>   __se_sys_sendmsg net/socket.c:2674 [inline]
>   __x64_sys_sendmsg+0x1bd/0x2a0 net/socket.c:2674
>   do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>   do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
>   entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7facf899c819
> Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007facf9827028 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
> RAX: ffffffffffffffda RBX: 00007facf8c15fa0 RCX: 00007facf899c819
> RDX: 0000000000000000 RSI: 0000200000000500 RDI: 0000000000000004
> RBP: 00007facf8a32c91 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> R13: 00007facf8c16038 R14: 00007facf8c15fa0 R15: 00007ffd41b01c78
>   </TASK>
[...]
>
> Fixes: c63829182c37 ("af_unix: Implement ->psock_update_sk_prot()")
> Reported-by: syzbot+2184232f07e3677fbaef@syzkaller.appspotmail.com
> Closes: https://lore.kernel.org/bpf/69cc6b9f.a70a0220.128fd0.004b.GAE@google.com/
> Signed-off-by: Kuniyuki Iwashima <kuniyu@google.com>


Reviewed-by: Jiayuan Chen <jiayuan.chen@linux.dev>

> ---
>   net/core/skmsg.c | 13 ++++++++-----
>   1 file changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/net/core/skmsg.c b/net/core/skmsg.c
> index 3261793abe83..6187a83bd741 100644
> --- a/net/core/skmsg.c
> +++ b/net/core/skmsg.c
> @@ -1267,17 +1267,20 @@ static int sk_psock_verdict_recv(struct sock *sk, struct sk_buff *skb)
>   
>   static void sk_psock_verdict_data_ready(struct sock *sk)
>   {
> -	struct socket *sock = sk->sk_socket;
> -	const struct proto_ops *ops;
> +	const struct proto_ops *ops = NULL;
> +	struct socket *sock;
>   	int copied;
>   
>   	trace_sk_data_ready(sk);
>   
> -	if (unlikely(!sock))
> -		return;
> -	ops = READ_ONCE(sock->ops);
> +	rcu_read_lock();
> +	sock = READ_ONCE(sk->sk_socket);
> +	if (likely(sock))
> +		ops = READ_ONCE(sock->ops);
> +	rcu_read_unlock();
>   	if (!ops || !ops->read_skb)
>   		return;
> +
>   	copied = ops->read_skb(sk, sk_psock_verdict_recv);
>   	if (copied >= 0) {
>   		struct sk_psock *psock;

Re: [PATCH v1 bpf] sockmap: Fix use-after-free of sk->sk_socket in sk_psock_verdict_data_ready().

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to bpf/bpf.git (master)
by Martin KaFai Lau <martin.lau@kernel.org>:

On Wed,  1 Apr 2026 00:54:15 +0000 you wrote:
> syzbot reported use-after-free of AF_UNIX socket's sk->sk_socket
> in sk_psock_verdict_data_ready(). [0]
> 
> In unix_stream_sendmsg(), the peer socket's ->sk_data_ready() is
> called after dropping its unix_state_lock().
> 
> Although the sender socket holds the peer's refcount, it does not
> prevent the peer's sock_orphan(), and the peer's sk_socket might
> be freed after one RCU grace period.
> 
> [...]

Here is the summary with links:
  - [v1,bpf] sockmap: Fix use-after-free of sk->sk_socket in sk_psock_verdict_data_ready().
    https://git.kernel.org/bpf/bpf/c/ad8391d37f33

You are awesome, thank you!
-- 
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