CVE-2024-47711

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

af_unix: Don't return OOB skb in manage_oob().

syzbot reported use-after-free in unix_stream_recv_urg(). [0]

The scenario is

1. send(MSG_OOB)
2. recv(MSG_OOB) -> The consumed OOB remains in recv queue
3. send(MSG_OOB)
4. recv() -> manage_oob() returns the next skb of the consumed OOB -> This is also OOB, but unix_sk(sk)->oob_skb is not cleared
5. recv(MSG_OOB) -> unix_sk(sk)->oob_skb is used but already freed

The recent commit 8594d9b85c07 ("af_unix: Don't call skb_get() for OOB skb.") uncovered the issue.

If the OOB skb is consumed and the next skb is peeked in manage_oob(), we still need to check if the skb is OOB.

Let's do so by falling back to the following checks in manage_oob() and add the test case in selftest.

Note that we need to add a similar check for SIOCATMARK.

[0]: BUG: KASAN: slab-use-after-free in unix_stream_read_actor+0xa6/0xb0 net/unix/af_unix.c:2959 Read of size 4 at addr ffff8880326abcc4 by task syz-executor178/5235

CPU: 0 UID: 0 PID: 5235 Comm: syz-executor178 Not tainted 6.11.0-rc5-syzkaller-00742-gfbdaffe41adc #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/06/2024 Call Trace: <TASK> __dump_stack lib/dump_stack.c:93 [inline] dump_stack_lvl+0x241/0x360 lib/dump_stack.c:119 print_address_description mm/kasan/report.c:377 [inline] print_report+0x169/0x550 mm/kasan/report.c:488 kasan_report+0x143/0x180 mm/kasan/report.c:601 unix_stream_read_actor+0xa6/0xb0 net/unix/af_unix.c:2959 unix_stream_recv_urg+0x1df/0x320 net/unix/af_unix.c:2640 unix_stream_read_generic+0x2456/0x2520 net/unix/af_unix.c:2778 unix_stream_recvmsg+0x22b/0x2c0 net/unix/af_unix.c:2996 sock_recvmsg_nosec net/socket.c:1046 [inline] sock_recvmsg+0x22f/0x280 net/socket.c:1068 ____sys_recvmsg+0x1db/0x470 net/socket.c:2816 ___sys_recvmsg net/socket.c:2858 [inline] __sys_recvmsg+0x2f0/0x3e0 net/socket.c:2888 do_syscall_x64...