[PATCH 4.16 059/272] sr: get/drop reference to device in revalidate and check_events

Greg Kroah-Hartman
2018-05-28T11:06:41Z

From: Jens Axboe <axboe@kernel.dk>

[ Upstream commit 2d097c50212e137e7b53ffe3b37561153eeba87d ]

We can't just use scsi_cd() to get the scsi_cd structure, we have
to grab a live reference to the device. For both callbacks, we're
not inside an open where we already hold a reference to the device.

This fixes device removal/addition under concurrent device access,
which otherwise could result in the below oops.

NULL pointer dereference at 0000000000000010
PGD 0 P4D 0
Oops: 0000 [#1] PREEMPT SMP
Modules linked in:
sr 12:0:0:0: [sr2] scsi-1 drive
scsi_debug crc_t10dif crct10dif_generic crct10dif_common nvme nvme_core sb_edac xl
sr 12:0:0:0: Attached scsi CD-ROM sr2
sr_mod cdrom btrfs xor zstd_decompress zstd_compress xxhash lzo_compress zlib_defc
sr 12:0:0:0: Attached scsi generic sg7 type 5
igb ahci libahci i2c_algo_bit libata dca [last unloaded: crc_t10dif]
CPU: 43 PID: 4629 Comm: systemd-udevd Not tainted 4.16.0+ #650
Hardware name: Dell Inc. PowerEdge T630/0NT78X, BIOS 2.3.4 11/09/2016
RIP: 0010:sr_block_revalidate_disk+0x23/0x190 [sr_mod]
RSP: 0018:ffff883ff357bb58 EFLAGS: 00010292
RAX: ffffffffa00b07d0 RBX: ffff883ff3058000 RCX: ffff883ff357bb66
RDX: 0000000000000003 RSI: 0000000000007530 RDI: ffff881fea631000
RBP: 0000000000000000 R08: ffff881fe4d38400 R09: 0000000000000000
R10: 0000000000000000 R11: 00000000000001b6 R12: 000000000800005d
R13: 000000000800005d R14: ffff883ffd9b3790 R15: 0000000000000000
FS: 00007f7dc8e6d8c0(0000) GS:ffff883fff340000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000010 CR3: 0000003ffda98005 CR4: 00000000003606e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
? __invalidate_device+0x48/0x60
check_disk_change+0x4c/0x60
sr_block_open+0x16/0xd0 [sr_mod]
__blkdev_get+0xb9/0x450
? iget5_locked+0x1c0/0x1e0
blkdev_get+0x11e/0x320
? bdget+0x11d/0x150
? _raw_spin_unlock+0xa/0x20
? bd_acquire+0xc0/0xc0
do_dentry_open+0x1b0/0x320
? inode_permission+0x24/0xc0
path_openat+0x4e6/0x1420
? cpumask_any_but+0x1f/0x40
? flush_tlb_mm_range+0xa0/0x120
do_filp_open+0x8c/0xf0
? __seccomp_filter+0x28/0x230
? _raw_spin_unlock+0xa/0x20
? __handle_mm_fault+0x7d6/0x9b0
? list_lru_add+0xa8/0xc0
? _raw_spin_unlock+0xa/0x20
? __alloc_fd+0xaf/0x160
? do_sys_open+0x1a6/0x230
do_sys_open+0x1a6/0x230
do_syscall_64+0x5a/0x100
entry_SYSCALL_64_after_hwframe+0x3d/0xa2

Reviewed-by: Lee Duncan <lduncan@suse.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/scsi/sr.c | 19 +++++++++++++++----
1 file changed, 15 insertions(+), 4 deletions(-)

--- a/drivers/scsi/sr.c
+++ b/drivers/scsi/sr.c
@@ -585,18 +585,28 @@ out:
static unsigned int sr_block_check_events(struct gendisk *disk,
unsigned int clearing)
{
- struct scsi_cd *cd = scsi_cd(disk);
+ unsigned int ret = 0;
+ struct scsi_cd *cd;

- if (atomic_read(&cd->device->disk_events_disable_depth))
+ cd = scsi_cd_get(disk);
+ if (!cd)
return 0;

- return cdrom_check_events(&cd->cdi, clearing);
+ if (!atomic_read(&cd->device->disk_events_disable_depth))
+ ret = cdrom_check_events(&cd->cdi, clearing);
+
+ scsi_cd_put(cd);
+ return ret;
}

static int sr_block_revalidate_disk(struct gendisk *disk)
{
- struct scsi_cd *cd = scsi_cd(disk);
struct scsi_sense_hdr sshdr;
+ struct scsi_cd *cd;
+
+ cd = scsi_cd_get(disk);
+ if (!cd)
+ return -ENXIO;

/* if the unit is not ready, nothing more to do */
if (scsi_test_unit_ready(cd->device, SR_TIMEOUT, MAX_RETRIES, &sshdr))
@@ -605,6 +615,7 @@ static int sr_block_revalidate_disk(stru
sr_cd_check(&cd->cdi);
get_sectorsize(cd);
out:
+ scsi_cd_put(cd);
return 0;
}