CVE-2024-36972

In the Linux kernel, the following vulnerability has been resolved:

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

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