Re: [PATCH] nvme-multipath: fix bogus request queue reference put

[Sagi Grimberg]

On 1/17/24 08:50, mengfanhui wrote:
> From: Sagi Grimberg <sagi@xxxxxxxxxxx>
>
> The mpath disk node takes a reference on the request mpath
> request queue when adding live path to the mpath gendisk.
> However if we connected to an inaccessible path device_add_disk
> is not called, so if we disconnect and remove the mpath gendisk
> we endup putting an reference on the request queue that was
> never taken [1].
>
> Fix that to check if we ever added a live path (using
> NVME_NS_HEAD_HAS_DISK flag) and if not, clear the disk->queue
> reference.
>
> [1]:
> ------------[ cut here ]------------
> refcount_t: underflow; use-after-free.
> WARNING: CPU: 1 PID: 1372 at lib/refcount.c:28 refcount_warn_saturate+0xa6/0xf0
> CPU: 1 PID: 1372 Comm: nvme Tainted: G           O      5.7.0-rc2+ #3
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.13.0-1ubuntu1 04/01/2014
> RIP: 0010:refcount_warn_saturate+0xa6/0xf0
> RSP: 0018:ffffb29e8053bdc0 EFLAGS: 00010282
> RAX: 0000000000000000 RBX: ffff8b7a2f4fc060 RCX: 0000000000000007
> RDX: 0000000000000007 RSI: 0000000000000092 RDI: ffff8b7a3ec99980
> RBP: ffff8b7a2f4fc000 R08: 00000000000002e1 R09: 0000000000000004
> R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000000
> R13: fffffffffffffff2 R14: ffffb29e8053bf08 R15: ffff8b7a320e2da0
> FS:  00007f135d4ca800(0000) GS:ffff8b7a3ec80000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00005651178c0c30 CR3: 000000003b650005 CR4: 0000000000360ee0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
>   disk_release+0xa2/0xc0
>   device_release+0x28/0x80
>   kobject_put+0xa5/0x1b0
>   nvme_put_ns_head+0x26/0x70 [nvme_core]
>   nvme_put_ns+0x30/0x60 [nvme_core]
>   nvme_remove_namespaces+0x9b/0xe0 [nvme_core]
>   nvme_do_delete_ctrl+0x43/0x5c [nvme_core]
>   nvme_sysfs_delete.cold+0x8/0xd [nvme_core]
>   kernfs_fop_write+0xc1/0x1a0
>   vfs_write+0xb6/0x1a0
>   ksys_write+0x5f/0xe0
>   do_syscall_64+0x52/0x1a0
>   entry_SYSCALL_64_after_hwframe+0x44/0xa9
>
> Signed-off-by: Sagi Grimberg <sagi@xxxxxxxxxxx>
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> Signed-off-by: mengfanhui <mengfanhui@xxxxxxxxxx>
> ---
>   drivers/nvme/host/multipath.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
>
> diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
> index 2dd4137a08b2..3e579e49579c 100644
> --- a/drivers/nvme/host/multipath.c
> +++ b/drivers/nvme/host/multipath.c
> @@ -895,6 +895,14 @@ void nvme_mpath_remove_disk(struct nvme_ns_head *head)
>   	/* make sure all pending bios are cleaned up */
>   	kblockd_schedule_work(&head->requeue_work);
>   	flush_work(&head->requeue_work);
> +	if (!test_bit(NVME_NSHEAD_DISK_LIVE, &head->flags)) {
> +		/*
> +		* if device_add_disk wasn't called, prevent
> +                * disk release to put a bogus reference on the
> +                * request queue
> +                */
> +		head->disk->queue = NULL;
> +	}
>   	put_disk(head->disk);
>   }
>   

How did you see this? disk->queue is allocated in blk_alloc_disk called
in nvme_mpath_alloc_disk... I don't understand how you saw the same
dereference that was addressed by this commit.