[PATCH 4.4 059/135] block: Fix use-after-free in blkdev_get()

From: Sasha Levin
Date: Mon Jun 29 2020 - 15:01:00 EST

From: Jason Yan <yanaijie@xxxxxxxxxx>

[ Upstream commit 2d3a8e2deddea6c89961c422ec0c5b851e648c14 ]

In blkdev_get() we call __blkdev_get() to do some internal jobs and if
there is some errors in __blkdev_get(), the bdput() is called which
means we have released the refcount of the bdev (actually the refcount of
the bdev inode). This means we cannot access bdev after that point. But
acctually bdev is still accessed in blkdev_get() after calling
__blkdev_get(). This results in use-after-free if the refcount is the
last one we released in __blkdev_get(). Let's take a look at the
following scenerio:

CPU0 CPU1 CPU2
blkdev_open blkdev_open Remove disk
bd_acquire
blkdev_get
__blkdev_get del_gendisk
bdev_unhash_inode
bd_acquire bdev_get_gendisk
bd_forget failed because of unhashed
bdput
bdput (the last one)
bdev_evict_inode

access bdev => use after free

[ 459.350216] BUG: KASAN: use-after-free in __lock_acquire+0x24c1/0x31b0
[ 459.351190] Read of size 8 at addr ffff88806c815a80 by task syz-executor.0/20132
[ 459.352347]
[ 459.352594] CPU: 0 PID: 20132 Comm: syz-executor.0 Not tainted 4.19.90 #2
[ 459.353628] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014
[ 459.354947] Call Trace:
[ 459.355337] dump_stack+0x111/0x19e
[ 459.355879] ? __lock_acquire+0x24c1/0x31b0
[ 459.356523] print_address_description+0x60/0x223
[ 459.357248] ? __lock_acquire+0x24c1/0x31b0
[ 459.357887] kasan_report.cold+0xae/0x2d8
[ 459.358503] __lock_acquire+0x24c1/0x31b0
[ 459.359120] ? _raw_spin_unlock_irq+0x24/0x40
[ 459.359784] ? lockdep_hardirqs_on+0x37b/0x580
[ 459.360465] ? _raw_spin_unlock_irq+0x24/0x40
[ 459.361123] ? finish_task_switch+0x125/0x600
[ 459.361812] ? finish_task_switch+0xee/0x600
[ 459.362471] ? mark_held_locks+0xf0/0xf0
[ 459.363108] ? __schedule+0x96f/0x21d0
[ 459.363716] lock_acquire+0x111/0x320
[ 459.364285] ? blkdev_get+0xce/0xbe0
[ 459.364846] ? blkdev_get+0xce/0xbe0
[ 459.365390] __mutex_lock+0xf9/0x12a0
[ 459.365948] ? blkdev_get+0xce/0xbe0
[ 459.366493] ? bdev_evict_inode+0x1f0/0x1f0
[ 459.367130] ? blkdev_get+0xce/0xbe0
[ 459.367678] ? destroy_inode+0xbc/0x110
[ 459.368261] ? mutex_trylock+0x1a0/0x1a0
[ 459.368867] ? __blkdev_get+0x3e6/0x1280
[ 459.369463] ? bdev_disk_changed+0x1d0/0x1d0
[ 459.370114] ? blkdev_get+0xce/0xbe0
[ 459.370656] blkdev_get+0xce/0xbe0
[ 459.371178] ? find_held_lock+0x2c/0x110
[ 459.371774] ? __blkdev_get+0x1280/0x1280
[ 459.372383] ? lock_downgrade+0x680/0x680
[ 459.373002] ? lock_acquire+0x111/0x320
[ 459.373587] ? bd_acquire+0x21/0x2c0
[ 459.374134] ? do_raw_spin_unlock+0x4f/0x250
[ 459.374780] blkdev_open+0x202/0x290
[ 459.375325] do_dentry_open+0x49e/0x1050
[ 459.375924] ? blkdev_get_by_dev+0x70/0x70
[ 459.376543] ? __x64_sys_fchdir+0x1f0/0x1f0
[ 459.377192] ? inode_permission+0xbe/0x3a0
[ 459.377818] path_openat+0x148c/0x3f50
[ 459.378392] ? kmem_cache_alloc+0xd5/0x280
[ 459.379016] ? entry_SYSCALL_64_after_hwframe+0x49/0xbe
[ 459.379802] ? path_lookupat.isra.0+0x900/0x900
[ 459.380489] ? __lock_is_held+0xad/0x140
[ 459.381093] do_filp_open+0x1a1/0x280
[ 459.381654] ? may_open_dev+0xf0/0xf0
[ 459.382214] ? find_held_lock+0x2c/0x110
[ 459.382816] ? lock_downgrade+0x680/0x680
[ 459.383425] ? __lock_is_held+0xad/0x140
[ 459.384024] ? do_raw_spin_unlock+0x4f/0x250
[ 459.384668] ? _raw_spin_unlock+0x1f/0x30
[ 459.385280] ? __alloc_fd+0x448/0x560
[ 459.385841] do_sys_open+0x3c3/0x500
[ 459.386386] ? filp_open+0x70/0x70
[ 459.386911] ? trace_hardirqs_on_thunk+0x1a/0x1c
[ 459.387610] ? trace_hardirqs_off_caller+0x55/0x1c0
[ 459.388342] ? do_syscall_64+0x1a/0x520
[ 459.388930] do_syscall_64+0xc3/0x520
[ 459.389490] entry_SYSCALL_64_after_hwframe+0x49/0xbe
[ 459.390248] RIP: 0033:0x416211
[ 459.390720] Code: 75 14 b8 02 00 00 00 0f 05 48 3d 01 f0 ff ff 0f 83
04 19 00 00 c3 48 83 ec 08 e8 0a fa ff ff 48 89 04 24 b8 02 00 00 00 0f
05 <48> 8b 3c 24 48 89 c2 e8 53 fa ff ff 48 89 d0 48 83 c4 08 48 3d
01
[ 459.393483] RSP: 002b:00007fe45dfe9a60 EFLAGS: 00000293 ORIG_RAX: 0000000000000002
[ 459.394610] RAX: ffffffffffffffda RBX: 00007fe45dfea6d4 RCX: 0000000000416211
[ 459.395678] RDX: 00007fe45dfe9b0a RSI: 0000000000000002 RDI: 00007fe45dfe9b00
[ 459.396758] RBP: 000000000076bf20 R08: 0000000000000000 R09: 000000000000000a
[ 459.397930] R10: 0000000000000075 R11: 0000000000000293 R12: 00000000ffffffff
[ 459.399022] R13: 0000000000000bd9 R14: 00000000004cdb80 R15: 000000000076bf2c
[ 459.400168]
[ 459.400430] Allocated by task 20132:
[ 459.401038] kasan_kmalloc+0xbf/0xe0
[ 459.401652] kmem_cache_alloc+0xd5/0x280
[ 459.402330] bdev_alloc_inode+0x18/0x40
[ 459.402970] alloc_inode+0x5f/0x180
[ 459.403510] iget5_locked+0x57/0xd0
[ 459.404095] bdget+0x94/0x4e0
[ 459.404607] bd_acquire+0xfa/0x2c0
[ 459.405113] blkdev_open+0x110/0x290
[ 459.405702] do_dentry_open+0x49e/0x1050
[ 459.406340] path_openat+0x148c/0x3f50
[ 459.406926] do_filp_open+0x1a1/0x280
[ 459.407471] do_sys_open+0x3c3/0x500
[ 459.408010] do_syscall_64+0xc3/0x520
[ 459.408572] entry_SYSCALL_64_after_hwframe+0x49/0xbe
[ 459.409415]
[ 459.409679] Freed by task 1262:
[ 459.410212] __kasan_slab_free+0x129/0x170
[ 459.410919] kmem_cache_free+0xb2/0x2a0
[ 459.411564] rcu_process_callbacks+0xbb2/0x2320
[ 459.412318] __do_softirq+0x225/0x8ac

Fix this by delaying bdput() to the end of blkdev_get() which means we
have finished accessing bdev.

Fixes: 77ea887e433a ("implement in-kernel gendisk events handling")
Reported-by: Hulk Robot <hulkci@xxxxxxxxxx>
Signed-off-by: Jason Yan <yanaijie@xxxxxxxxxx>
Tested-by: Sedat Dilek <sedat.dilek@xxxxxxxxx>
Reviewed-by: Jan Kara <jack@xxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Reviewed-by: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxx>
Cc: Jens Axboe <axboe@xxxxxxxxx>
Cc: Ming Lei <ming.lei@xxxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Dan Carpenter <dan.carpenter@xxxxxxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
fs/block_dev.c | 12 +++++++-----
1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 26bbaaefdff48..b2ebfd96785b7 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -1181,10 +1181,8 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
*/
if (!for_part) {
ret = devcgroup_inode_permission(bdev->bd_inode, perm);
- if (ret != 0) {
- bdput(bdev);
+ if (ret != 0)
return ret;
- }
}

restart:
@@ -1253,8 +1251,10 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
goto out_clear;
BUG_ON(for_part);
ret = __blkdev_get(whole, mode, 1);
- if (ret)
+ if (ret) {
+ bdput(whole);
goto out_clear;
+ }
bdev->bd_contains = whole;
bdev->bd_part = disk_get_part(disk, partno);
if (!(disk->flags & GENHD_FL_UP) ||
@@ -1311,7 +1311,6 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
put_disk(disk);
module_put(owner);
out:
- bdput(bdev);

return ret;
}
@@ -1397,6 +1396,9 @@ int blkdev_get(struct block_device *bdev, fmode_t mode, void *holder)
bdput(whole);
}

+ if (res)
+ bdput(bdev);
+
return res;
}
EXPORT_SYMBOL(blkdev_get);
--
2.25.1