linux-kernel - cdrom: cdrom_mrw_exit() NULL ptr deref

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Message-ID: <uxgzea5ibqxygv3x7i4ojbpvcpv2wziorvb3ns5cdtyvobyn7h@y4g4l5ezv2ec>
Date: Fri, 11 Jul 2025 16:04:17 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Phillip Potter <phil@...lpotter.co.uk>, Jens Axboe <axboe@...nel.dk>
Cc: Christoph Hellwig <hch@...radead.org>, 
	Chris Rankin <rankincj@...il.com>, linux-kernel@...r.kernel.org, linux-block@...r.kernel.org, 
	Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: cdrom: cdrom_mrw_exit() NULL ptr deref

Hi,

We are seeing the same NULL ptr deref upon cdrom release, as reported
in [1] (Chris Cc-ed) in our fleet.  Currently on 6.6 LTS (could be the
same for older kernels as well, I didn't check.)

Phillip, is this a known issue?

<1>[335443.339244] BUG: kernel NULL pointer dereference, address: 0000000000000010
<1>[335443.339262] #PF: supervisor read access in kernel mode
<1>[335443.339268] #PF: error_code(0x0000) - not-present page
<6>[335443.339273] PGD 0 P4D 0
<4>[335443.339279] Oops: 0000 [#1] PREEMPT SMP NOPTI
<4>[335443.339287] CPU: 1 PID: 1988 Comm: cros-disks Not tainted 6.6.76-07501-gd42535a678fb #1 (HASH:7d84 1)
<4>[335443.339301] RIP: 0010:blk_queue_enter+0x5a/0x250
<4>[335443.339312] Code: 03 00 00 4c 8d 6d a8 eb 1c 4c 89 e7 4c 89 ee e8 8c 62 be ff 49 f7 86 88 00 00 00 02 00 00 00 0f 85 ce 01 00 00 e8 86 10 bd ff <49> 8b 07 a8 03 0f 85 85 01 00 00 65 48 ff 00 41 83 be 90 00 00 00
<4>[335443.339318] RSP: 0018:ffff9be08ab03b00 EFLAGS: 00010202
<4>[335443.339324] RAX: ffff8903aa366300 RBX: 0000000000000000 RCX: ffff9be08ab03cd0
<4>[335443.339330] RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
<4>[335443.339333] RBP: ffff9be08ab03b58 R08: 0000000000000002 R09: 0000000000001b58
<4>[335443.339338] R10: ffffffff00000000 R11: ffffffffc0ccd030 R12: 0000000000000328
<4>[335443.339344] R13: ffff9be08ab03b00 R14: 0000000000000000 R15: 0000000000000010
<4>[335443.339348] FS: 00007d52be81e900(0000) GS:ffff8904b6040000(0000) knlGS:0000000000000000
<4>[335443.339357] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
<4>[335443.339362] CR2: 0000000000000010 CR3: 0000000140ac6000 CR4: 0000000000350ee0
<4>[335443.339367] Call Trace:
<4>[335443.339372] <TASK>
<4>[335443.339379] ? __die_body+0xae/0xb0
<4>[335443.339389] ? page_fault_oops+0x381/0x3e0
<4>[335443.339398] ? exc_page_fault+0x4f/0xa0
<4>[335443.339404] ? asm_exc_page_fault+0x22/0x30
<4>[335443.339416] ? sr_check_events+0x290/0x290 [sr_mod (HASH:ab3e 2)]
<4>[335443.339432] ? blk_queue_enter+0x5a/0x250
<4>[335443.339439] blk_mq_alloc_request+0x16a/0x220
<4>[335443.339450] scsi_execute_cmd+0x65/0x240
<4>[335443.339458] sr_do_ioctl+0xe3/0x210 [sr_mod (HASH:ab3e 2)]
<4>[335443.339471] sr_packet+0x3d/0x50 [sr_mod (HASH:ab3e 2)]
<4>[335443.339482] cdrom_mrw_exit+0xc1/0x240 [cdrom (HASH:9d9a 3)]
<4>[335443.339497] sr_free_disk+0x45/0x60 [sr_mod (HASH:ab3e 2)]
<4>[335443.339506] disk_release+0xc8/0xe0
<4>[335443.339515] device_release+0x39/0x90
<4>[335443.339523] kobject_release+0x49/0xb0
<4>[335443.339533] bdev_release+0x19/0x30
<4>[335443.339540] deactivate_locked_super+0x3b/0x100
<4>[335443.339548] cleanup_mnt+0xaa/0x160
<4>[335443.339557] task_work_run+0x6c/0xb0
<4>[335443.339563] exit_to_user_mode_prepare+0x102/0x120
<4>[335443.339571] syscall_exit_to_user_mode+0x1a/0x30
<4>[335443.339577] do_syscall_64+0x7e/0xa0
<4>[335443.339582] ? exit_to_user_mode_prepare+0x44/0x120
<4>[335443.339588] entry_SYSCALL_64_after_hwframe+0x55/0xbf
<4>[335443.339595] RIP: 0033:0x7d52bea41f07

[1] https://lore.kernel.org/all/CAK2bqVJGsz8r8D-x=4N6p9nXQ=v4AwpMAg2frotmdSdtjvnexg@mail.gmail.com/