On Thu, Sep 02, 2021 at 01:57:13PM +0000, Christian Löhle wrote:
sd and parent devices must not be removed as sd_open checks for events
sd_need_revalidate and sd_revalidate_disk traverse the device path to check for event changes. If during this, e.g. the scsi host is being removed and its resources freed, this traversal crashes. Locking with scan_mutex for just a scsi disk open may seem blunt, but there does not seem to be a more granular option. Also opening /dev/sdX directly happens rarely enough that this shouldn't cause any issues.
The issue occurred on an older kernel with the following trace: stack segment: 0000 [#1] PREEMPT SMP PTI CPU: 1 PID: 121457 Comm: python3 Not tainted 4.14.238hyLinux #1 Hardware name: ASUS All Series/H81M-D, BIOS 0601 02/20/2014 task: ffff888213dbb700 task.stack: ffffc90008c14000 RIP: 0010:kobject_get_path+0x2a/0xe0 ... Call Trace: kobject_uevent_env+0xe6/0x550 disk_check_events+0x101/0x160 disk_clear_events+0x75/0x100 check_disk_change+0x22/0x60 sd_open+0x70/0x170 [sd_mod] __blkdev_get+0x3fd/0x4b0 ? get_empty_filp+0x57/0x1b0 blkdev_get+0x11b/0x330 ? bd_acquire+0xc0/0xc0 do_dentry_open+0x1ef/0x320 ? __inode_permission+0x85/0xc0 path_openat+0x5cb/0x1500 ? terminate_walk+0xeb/0x100 do_filp_open+0x9b/0x110 ? __check_object_size+0xb4/0x190 ? do_sys_open+0x1bd/0x250 do_sys_open+0x1bd/0x250 do_syscall_64+0x67/0x120 entry_SYSCALL_64_after_hwframe+0x41/0xa6
and this commit fixed that issue, as there has been no other such synchronization in place since then, the issue should still be present in recent kernels.
Signed-off-by: Christian Loehle cloehle@hyperstone.com
drivers/scsi/sd.c | 20 +++++++++++++++++--- 1 file changed, 17 insertions(+), 3 deletions(-)
diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c index 610ebba0d66e..ad4da985a473 100644 --- a/drivers/scsi/sd.c +++ b/drivers/scsi/sd.c @@ -1436,6 +1436,16 @@ static int sd_open(struct block_device *bdev, fmode_t mode) if (!scsi_block_when_processing_errors(sdev)) goto error_out;
- /*
* Checking for changes to the device must not race with the device* or its parent host being removed, so lock until sd_open returns.*/- mutex_lock(&sdev->host->scan_mutex);
- if (sdev->sdev_state != SDEV_RUNNING) {
retval = -ERESTARTSYS;goto unlock_scan_error_out;- }
- if (sd_need_revalidate(bdev, sdkp)) sd_revalidate_disk(bdev->bd_disk);
@@ -1444,7 +1454,7 @@ static int sd_open(struct block_device *bdev, fmode_t mode) */ retval = -ENOMEDIUM; if (sdev->removable && !sdkp->media_present && !(mode & FMODE_NDELAY))
goto error_out;
goto unlock_scan_error_out;/* * If the device has the write protect tab set, have the open fail @@ -1452,7 +1462,7 @@ static int sd_open(struct block_device *bdev, fmode_t mode) */ retval = -EROFS; if (sdkp->write_prot && (mode & FMODE_WRITE))
goto error_out;
goto unlock_scan_error_out;/* * It is possible that the disk changing stuff resulted in @@ -1462,15 +1472,19 @@ static int sd_open(struct block_device *bdev, fmode_t mode) */ retval = -ENXIO; if (!scsi_device_online(sdev))
goto error_out;
goto unlock_scan_error_out;if ((atomic_inc_return(&sdkp->openers) == 1) && sdev->removable) { if (scsi_block_when_processing_errors(sdev)) scsi_set_medium_removal(sdev, SCSI_REMOVAL_PREVENT); }
- mutex_unlock(&sdev->host->scan_mutex); return 0;
+unlock_scan_error_out:
- mutex_unlock(&sdev->host->scan_mutex);
error_out: scsi_disk_put(sdkp); return retval; -- 2.32.0= Hyperstone GmbH | Line-Eid-Strasse 3 | 78467 Konstanz Managing Directors: Dr. Jan Peter Berns. Commercial register of local courts: Freiburg HRB381782
<formletter>
This is not the correct way to submit patches for inclusion in the stable kernel tree. Please read: https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html for how to do this properly.
</formletter>