CVE-2022-50070

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

mptcp: do not queue data on closed subflows

Dipanjan reported a syzbot splat at close time:

WARNING: CPU: 1 PID: 10818 at net/ipv4/afinet.c:153 inetsockdestruct+0x6d0/0x8e0 net/ipv4/afinet.c:153 Modules linked in: uioivshmem(OE) uio(E) CPU: 1 PID: 10818 Comm: kworker/1:16 Tainted: G OE 5.19.0-rc6-g2eae0556bb9d #2 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014 Workqueue: events mptcpworker RIP: 0010:inetsockdestruct+0x6d0/0x8e0 net/ipv4/af_inet.c:153 Code: 21 02 00 00 41 8b 9c 24 28 02 00 00 e9 07 ff ff ff e8 34 4d 91 f9 89 ee 4c 89 e7 e8 4a 47 60 ff e9 a6 fc ff ff e8 20 4d 91 f9 <0f> 0b e9 84 fe ff ff e8 14 4d 91 f9 0f 0b e9 d4 fd ff ff e8 08 4d RSP: 0018:ffffc9001b35fa78 EFLAGS: 00010246 RAX: 0000000000000000 RBX: 00000000002879d0 RCX: ffff8881326f3b00 RDX: 0000000000000000 RSI: ffff8881326f3b00 RDI: 0000000000000002 RBP: ffff888179662674 R08: ffffffff87e983a0 R09: 0000000000000000 R10: 0000000000000005 R11: 00000000000004ea R12: ffff888179662400 R13: ffff888179662428 R14: 0000000000000001 R15: ffff88817e38e258 FS: 0000000000000000(0000) GS:ffff8881f5f00000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 0000000020007bc0 CR3: 0000000179592000 CR4: 0000000000150ee0 Call Trace: <TASK> __skdestruct+0x4f/0x8e0 net/core/sock.c:2067 skdestruct+0xbd/0xe0 net/core/sock.c:2112 __skfree+0xef/0x3d0 net/core/sock.c:2123 skfree+0x78/0xa0 net/core/sock.c:2134 sock_put include/net/sock.h:1927 [inline] __mptcpclosessk+0x50f/0x780 net/mptcp/protocol.c:2351 _mptcpdestroysock+0x332/0x760 net/mptcp/protocol.c:2828 mptcpworker+0x5d2/0xc90 net/mptcp/protocol.c:2586 processonework+0x9cc/0x1650 kernel/workqueue.c:2289 workerthread+0x623/0x1070 kernel/workqueue.c:2436 kthread+0x2e9/0x3a0 kernel/kthread.c:376 retfromfork+0x1f/0x30 arch/x86/entry/entry64.S:302 </TASK>

The root cause of the problem is that an mptcp-level (re)transmit can race with mptcp_close() and the packet scheduler checks the subflow state before acquiring the socket lock: we can try to (re)transmit on an already closed ssk.

Fix the issue checking again the subflow socket status under the subflow socket lock protection. Additionally add the missing check for the fallback-to-tcp case.