CVE-2024-50082: In the Linux kernel, the following vulnerability has been resolved:  blk-rq-qos: fix crash on rq_qos_wait vs. rq_qos_wake_function race  We're seeing crashes from rq_qos_wake_function that look like this:    BUG: unable to handle page fault for address: ffffafe180a40084   #PF: supervisor write access in kernel mode   #PF: error_code(0x0002) - not-present page   PGD 100000067 P4D 100000067 PUD 10027c067 PMD 10115d067 PTE 0   Oops: Oops: 0002 [#1] PREEMPT SMP PTI   CPU: 17 UID: 0 PID: 0 Comm: swapper/17 Not tainted 6.12.0-rc3-00013-geca631b8fe80 #11   Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.16.0-0-gd239552ce722-prebuilt.qemu.org 04/01/2014   RIP: 0010:_raw_spin_lock_irqsave+0x1d/0x40   Code: 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa 0f 1f 44 00 00 41 54 9c 41 5c fa 65 ff 05 62 97 30 4c 31 c0 ba 01 00 00 00 <f0> 0f b1 17 75 0a 4c 89 e0 41 5c c3 cc cc cc cc 89 c6 e8 2c 0b 00   RSP: 0018:ffffafe180580ca0 EFLAGS: 00010046   RAX: 0000000000000000 RBX: ffffafe180a3f7a8 RCX: 0000000000000011   RDX: 0000000000000001 RSI: 0000000000000003 RDI: ffffafe180a40084   RBP: 0000000000000000 R08: 00000000001e7240 R09: 0000000000000011   R10: 0000000000000028 R11: 0000000000000888 R12: 0000000000000002   R13: ffffafe180a40084 R14: 0000000000000000 R15: 0000000000000003   FS:  0000000000000000(0000) GS:ffff9aaf1f280000(0000) knlGS:0000000000000000   CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033   CR2: ffffafe180a40084 CR3: 000000010e428002 CR4: 0000000000770ef0   DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000   DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400   PKRU: 55555554   Call Trace:    <IRQ>    try_to_wake_up+0x5a/0x6a0    rq_qos_wake_function+0x71/0x80    __wake_up_common+0x75/0xa0    __wake_up+0x36/0x60    scale_up.part.0+0x50/0x110    wb_timer_fn+0x227/0x450    ...  So rq_qos_wake_function() calls wake_up_process(data->task), which calls try_to_wake_up(), which faults in raw_spin_lock_irqsave(&p->pi_lock).  p comes from data->task, and data comes from the waitqueue entry, which is stored on the waiter's stack in rq_qos_wait(). Analyzing the core dump with drgn, I found that the waiter had already woken up and moved on to a completely unrelated code path, clobbering what was previously data->task. Meanwhile, the waker was passing the clobbered garbage in data->task to wake_up_process(), leading to the crash.  What's happening is that in between rq_qos_wake_function() deleting the waitqueue entry and calling wake_up_process(), rq_qos_wait() is finding that it already got a token and returning. The race looks like this:  rq_qos_wait()                           rq_qos_wake_function() ============================================================== prepare_to_wait_exclusive()                                         data->got_token = true;                                         list_del_init(&curr->entry); if (data.got_token)         break; finish_wait(&rqw->wait, &data.wq);   ^- returns immediately because      list_empty_careful(&wq_entry->entry)      is true ... return, go do something else ...                                         wake_up_process(data->task)                                           (NO LONGER VALID!)-^  Normally, finish_wait() is supposed to synchronize against the waker. But, as noted above, it is returning immediately because the waitqueue entry has already been removed from the waitqueue.  The bug is that rq_qos_wake_function() is accessing the waitqueue entry AFTER deleting it. Note that autoremove_wake_function() wakes the waiter and THEN deletes the waitqueue entry, which is the proper order.  Fix it by swapping the order. We also need to use list_del_init_careful() to match the list_empty_careful() in finish_wait().