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Date: Mon, 30 May 2016 14:58:27 +0200
From: Markus Pargmann <mpa@...gutronix.de>
To: Vegard Nossum <vegard.nossum@...cle.com>
Cc: Jens Axboe <axboe@...com>,
Quentin Casasnovas <quentin.casasnovas@...cle.com>,
linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
Paul Clements <paul.clements@...eleye.com>,
Pavel Machek <pavel@...e.cz>, Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH] nbd: fix race in ioctl
Hi,
On Friday 27 May 2016 12:59:35 Vegard Nossum wrote:
> Quentin ran into this bug:
>
> WARNING: CPU: 64 PID: 10085 at fs/sysfs/dir.c:31 sysfs_warn_dup+0x65/0x80
> sysfs: cannot create duplicate filename '/devices/virtual/block/nbd3/pid'
> Modules linked in: nbd
> CPU: 64 PID: 10085 Comm: qemu-nbd Tainted: G D 4.6.0+ #7
> 0000000000000000 ffff8820330bba68 ffffffff814b8791 ffff8820330bbac8
> 0000000000000000 ffff8820330bbab8 ffffffff810d04ab ffff8820330bbaa8
> 0000001f00000296 0000000000017681 ffff8810380bf000 ffffffffa0001790
> Call Trace:
> [<ffffffff814b8791>] dump_stack+0x4d/0x6c
> [<ffffffff810d04ab>] __warn+0xdb/0x100
> [<ffffffff810d0574>] warn_slowpath_fmt+0x44/0x50
> [<ffffffff81218c65>] sysfs_warn_dup+0x65/0x80
> [<ffffffff81218a02>] sysfs_add_file_mode_ns+0x172/0x180
> [<ffffffff81218a35>] sysfs_create_file_ns+0x25/0x30
> [<ffffffff81594a76>] device_create_file+0x36/0x90
> [<ffffffffa0000e8d>] __nbd_ioctl+0x32d/0x9b0 [nbd]
> [<ffffffff814cc8e8>] ? find_next_bit+0x18/0x20
> [<ffffffff810f7c29>] ? select_idle_sibling+0xe9/0x120
> [<ffffffff810f6cd7>] ? __enqueue_entity+0x67/0x70
> [<ffffffff810f9bf0>] ? enqueue_task_fair+0x630/0xe20
> [<ffffffff810efa76>] ? resched_curr+0x36/0x70
> [<ffffffff810f0078>] ? check_preempt_curr+0x78/0x90
> [<ffffffff810f00a2>] ? ttwu_do_wakeup+0x12/0x80
> [<ffffffff810f01b1>] ? ttwu_do_activate.constprop.86+0x61/0x70
> [<ffffffff810f0c15>] ? try_to_wake_up+0x185/0x2d0
> [<ffffffff810f0d6d>] ? default_wake_function+0xd/0x10
> [<ffffffff81105471>] ? autoremove_wake_function+0x11/0x40
> [<ffffffffa0001577>] nbd_ioctl+0x67/0x94 [nbd]
> [<ffffffff814ac0fd>] blkdev_ioctl+0x14d/0x940
> [<ffffffff811b0da2>] ? put_pipe_info+0x22/0x60
> [<ffffffff811d96cc>] block_ioctl+0x3c/0x40
> [<ffffffff811ba08d>] do_vfs_ioctl+0x8d/0x5e0
> [<ffffffff811aa329>] ? ____fput+0x9/0x10
> [<ffffffff810e9092>] ? task_work_run+0x72/0x90
> [<ffffffff811ba627>] SyS_ioctl+0x47/0x80
> [<ffffffff8185f5df>] entry_SYSCALL_64_fastpath+0x17/0x93
> ---[ end trace 7899b295e4f850c8 ]---
>
> It seems fairly obvious that device_create_file() is not being protected
> from being run concurrently on the same nbd.
>
> Quentin found the following relevant commits:
>
> 1a2ad21 nbd: add locking to nbd_ioctl
> 90b8f28 [PATCH] end of methods switch: remove the old ones
> d4430d6 [PATCH] beginning of methods conversion
> 08f8585 [PATCH] move block_device_operations to blkdev.h
>
> It would seem that the race was introduced in the process of moving nbd
> from BKL to unlocked ioctls.
>
> By setting nbd->task_recv while the mutex is held, we can prevent other
> processes from running concurrently (since nbd->task_recv is also checked
> while the mutex is held).
>
> Reported-and-tested-by: Quentin Casasnovas <quentin.casasnovas@...cle.com>
> Cc: Markus Pargmann <mpa@...gutronix.de>
> Cc: Paul Clements <paul.clements@...eleye.com>
> Cc: Pavel Machek <pavel@...e.cz>
> Cc: Jens Axboe <axboe@...com>
> Cc: Al Viro <viro@...iv.linux.org.uk>
> Signed-off-by: Vegard Nossum <vegard.nossum@...cle.com>
Thanks, applied.
Best Regards,
Markus
> ---
> drivers/block/nbd.c | 12 ++++--------
> 1 file changed, 4 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> index 31e73a7..a831f2b 100644
> --- a/drivers/block/nbd.c
> +++ b/drivers/block/nbd.c
> @@ -451,14 +451,9 @@ static int nbd_thread_recv(struct nbd_device *nbd, struct block_device *bdev)
>
> sk_set_memalloc(nbd->sock->sk);
>
> - nbd->task_recv = current;
> -
> ret = device_create_file(disk_to_dev(nbd->disk), &pid_attr);
> if (ret) {
> dev_err(disk_to_dev(nbd->disk), "device_create_file failed!\n");
> -
> - nbd->task_recv = NULL;
> -
> return ret;
> }
>
> @@ -477,9 +472,6 @@ static int nbd_thread_recv(struct nbd_device *nbd, struct block_device *bdev)
> nbd_size_clear(nbd, bdev);
>
> device_remove_file(disk_to_dev(nbd->disk), &pid_attr);
> -
> - nbd->task_recv = NULL;
> -
> return ret;
> }
>
> @@ -788,6 +780,8 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
> if (!nbd->sock)
> return -EINVAL;
>
> + /* We have to claim the device under the lock */
> + nbd->task_recv = current;
> mutex_unlock(&nbd->tx_lock);
>
> nbd_parse_flags(nbd, bdev);
> @@ -796,6 +790,7 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
> nbd_name(nbd));
> if (IS_ERR(thread)) {
> mutex_lock(&nbd->tx_lock);
> + nbd->task_recv = NULL;
> return PTR_ERR(thread);
> }
>
> @@ -805,6 +800,7 @@ static int __nbd_ioctl(struct block_device *bdev, struct nbd_device *nbd,
> kthread_stop(thread);
>
> mutex_lock(&nbd->tx_lock);
> + nbd->task_recv = NULL;
>
> sock_shutdown(nbd);
> nbd_clear_que(nbd);
>
--
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