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

mptcp: Correctly set DATA_FIN timeout when number of retransmits is large

Syzkaller with UBSAN uncovered a scenario where a large number of DATAFIN retransmits caused a shift-out-of-bounds in the DATAFIN timeout calculation:

================================================================================ UBSAN: shift-out-of-bounds in net/mptcp/protocol.c:470:29 shift exponent 32 is too large for 32-bit type 'unsigned int' CPU: 1 PID: 13059 Comm: kworker/1:0 Not tainted 5.17.0-rc2-00630-g5fbf21c90c60 #1 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.1 04/01/2014 Workqueue: events mptcp_worker Call Trace: <TASK> __dumpstack lib/dumpstack.c:88 [inline] dumpstacklvl+0xcd/0x134 lib/dumpstack.c:106 ubsanepilogue+0xb/0x5a lib/ubsan.c:151 __ubsanhandleshiftoutofbounds.cold+0xb2/0x20e lib/ubsan.c:330 mptcpsetdatafintimeout net/mptcp/protocol.c:470 [inline] __mptcpretrans.cold+0x72/0x77 net/mptcp/protocol.c:2445 mptcpworker+0x58a/0xa70 net/mptcp/protocol.c:2528 processonework+0x9df/0x16d0 kernel/workqueue.c:2307 workerthread+0x95/0xe10 kernel/workqueue.c:2454 kthread+0x2f4/0x3b0 kernel/kthread.c:377 retfromfork+0x1f/0x30 arch/x86/entry/entry64.S:295

</TASK>

This change limits the maximum timeout by limiting the size of the shift, which keeps all intermediate values in-bounds.