@@ -2217,13 +2217,20 @@ 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);
+
+ /* oob_skb must be changed under sk_recv_queue's
+ * lock to avoid the race with GC.
+ */
+ spin_lock(&other->sk_receive_queue.lock);
if (ousk->oob_skb)
consume_skb(ousk->oob_skb);
WRITE_ONCE(ousk->oob_skb, skb);
- scm_stat_add(other, skb);
- skb_queue_tail(&other->sk_receive_queue, skb);
+ __skb_queue_tail(&other->sk_receive_queue, skb);
+ spin_unlock(&other->sk_receive_queue.lock);
+
sk_send_sigurg(other);
unix_state_unlock(other);
other->sk_data_ready(other);
@@ -2614,8 +2621,10 @@ 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;
@@ -2627,6 +2636,8 @@ 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);
@@ -2655,6 +2666,10 @@ 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;
@@ -2666,13 +2681,19 @@ 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(skb));
+ kfree_skb(skb);
+ }
}
return skb;
}
@@ -342,10 +342,12 @@ static void __unix_gc(struct work_struct *work)
scan_children(&u->sk, inc_inflight, &hitlist);
#if IS_ENABLED(CONFIG_AF_UNIX_OOB)
+ spin_lock(&u->sk.sk_receive_queue.lock);
if (u->oob_skb) {
- kfree_skb(u->oob_skb);
+ WARN_ON_ONCE(skb_unref(u->oob_skb));
u->oob_skb = NULL;
}
+ spin_unlock(&u->sk.sk_receive_queue.lock);
#endif
}
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 the same issue exists in the new GC, and the change in queue_oob() can be applied as is. Also note that we change kfree_skb() to skb_unref() in __unix_gc() to make it clear that we don't actually free OOB skb there, and 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@rbox.co/ [1] Fixes: 1279f9d9dec2 ("af_unix: Call kfree_skb() for dead unix_(sk)->oob_skb in GC.") Reported-by: Billy Jheng Bing-Jhong <billy@starlabs.sg> Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com> --- v3: * Fix lockdep false-positive by calling kfree_skb outside of recvq lock in manage_oob() (Michal) v2: https://lore.kernel.org/netdev/20240510093905.25510-1-kuniyu@amazon.com/ * Add recvq locking everywhere we touch oob_skb (Paolo) v1: https://lore.kernel.org/netdev/20240507170018.83385-1-kuniyu@amazon.com/ --- net/unix/af_unix.c | 31 ++++++++++++++++++++++++++----- net/unix/garbage.c | 4 +++- 2 files changed, 29 insertions(+), 6 deletions(-)