This is a note to let you know that I've just added the patch titled
btrfs: fix use-after-free in btrfs_encoded_read_endio()
to the 6.12-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
btrfs-fix-use-after-free-in-btrfs_encoded_read_endio.patch
and it can be found in the queue-6.12 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit ab4e577cef12a57a5f647316735343913d037b29
Author: Johannes Thumshirn <johannes.thumshirn@xxxxxxx>
Date: Wed Nov 13 18:16:48 2024 +0100
btrfs: fix use-after-free in btrfs_encoded_read_endio()
[ Upstream commit 05b36b04d74a517d6675bf2f90829ff1ac7e28dc ]
Shinichiro reported the following use-after free that sometimes is
happening in our CI system when running fstests' btrfs/284 on a TCMU
runner device:
BUG: KASAN: slab-use-after-free in lock_release+0x708/0x780
Read of size 8 at addr ffff888106a83f18 by task kworker/u80:6/219
CPU: 8 UID: 0 PID: 219 Comm: kworker/u80:6 Not tainted 6.12.0-rc6-kts+ #15
Hardware name: Supermicro Super Server/X11SPi-TF, BIOS 3.3 02/21/2020
Workqueue: btrfs-endio btrfs_end_bio_work [btrfs]
Call Trace:
<TASK>
dump_stack_lvl+0x6e/0xa0
? lock_release+0x708/0x780
print_report+0x174/0x505
? lock_release+0x708/0x780
? __virt_addr_valid+0x224/0x410
? lock_release+0x708/0x780
kasan_report+0xda/0x1b0
? lock_release+0x708/0x780
? __wake_up+0x44/0x60
lock_release+0x708/0x780
? __pfx_lock_release+0x10/0x10
? __pfx_do_raw_spin_lock+0x10/0x10
? lock_is_held_type+0x9a/0x110
_raw_spin_unlock_irqrestore+0x1f/0x60
__wake_up+0x44/0x60
btrfs_encoded_read_endio+0x14b/0x190 [btrfs]
btrfs_check_read_bio+0x8d9/0x1360 [btrfs]
? lock_release+0x1b0/0x780
? trace_lock_acquire+0x12f/0x1a0
? __pfx_btrfs_check_read_bio+0x10/0x10 [btrfs]
? process_one_work+0x7e3/0x1460
? lock_acquire+0x31/0xc0
? process_one_work+0x7e3/0x1460
process_one_work+0x85c/0x1460
? __pfx_process_one_work+0x10/0x10
? assign_work+0x16c/0x240
worker_thread+0x5e6/0xfc0
? __pfx_worker_thread+0x10/0x10
kthread+0x2c3/0x3a0
? __pfx_kthread+0x10/0x10
ret_from_fork+0x31/0x70
? __pfx_kthread+0x10/0x10
ret_from_fork_asm+0x1a/0x30
</TASK>
Allocated by task 3661:
kasan_save_stack+0x30/0x50
kasan_save_track+0x14/0x30
__kasan_kmalloc+0xaa/0xb0
btrfs_encoded_read_regular_fill_pages+0x16c/0x6d0 [btrfs]
send_extent_data+0xf0f/0x24a0 [btrfs]
process_extent+0x48a/0x1830 [btrfs]
changed_cb+0x178b/0x2ea0 [btrfs]
btrfs_ioctl_send+0x3bf9/0x5c20 [btrfs]
_btrfs_ioctl_send+0x117/0x330 [btrfs]
btrfs_ioctl+0x184a/0x60a0 [btrfs]
__x64_sys_ioctl+0x12e/0x1a0
do_syscall_64+0x95/0x180
entry_SYSCALL_64_after_hwframe+0x76/0x7e
Freed by task 3661:
kasan_save_stack+0x30/0x50
kasan_save_track+0x14/0x30
kasan_save_free_info+0x3b/0x70
__kasan_slab_free+0x4f/0x70
kfree+0x143/0x490
btrfs_encoded_read_regular_fill_pages+0x531/0x6d0 [btrfs]
send_extent_data+0xf0f/0x24a0 [btrfs]
process_extent+0x48a/0x1830 [btrfs]
changed_cb+0x178b/0x2ea0 [btrfs]
btrfs_ioctl_send+0x3bf9/0x5c20 [btrfs]
_btrfs_ioctl_send+0x117/0x330 [btrfs]
btrfs_ioctl+0x184a/0x60a0 [btrfs]
__x64_sys_ioctl+0x12e/0x1a0
do_syscall_64+0x95/0x180
entry_SYSCALL_64_after_hwframe+0x76/0x7e
The buggy address belongs to the object at ffff888106a83f00
which belongs to the cache kmalloc-rnd-07-96 of size 96
The buggy address is located 24 bytes inside of
freed 96-byte region [ffff888106a83f00, ffff888106a83f60)
The buggy address belongs to the physical page:
page: refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff888106a83800 pfn:0x106a83
flags: 0x17ffffc0000000(node=0|zone=2|lastcpupid=0x1fffff)
page_type: f5(slab)
raw: 0017ffffc0000000 ffff888100053680 ffffea0004917200 0000000000000004
raw: ffff888106a83800 0000000080200019 00000001f5000000 0000000000000000
page dumped because: kasan: bad access detected
Memory state around the buggy address:
ffff888106a83e00: fa fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
ffff888106a83e80: fa fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
>ffff888106a83f00: fa fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
^
ffff888106a83f80: fa fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
ffff888106a84000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================
Further analyzing the trace and the crash dump's vmcore file shows that
the wake_up() call in btrfs_encoded_read_endio() is calling wake_up() on
the wait_queue that is in the private data passed to the end_io handler.
Commit 4ff47df40447 ("btrfs: move priv off stack in
btrfs_encoded_read_regular_fill_pages()") moved 'struct
btrfs_encoded_read_private' off the stack.
Before that commit one can see a corruption of the private data when
analyzing the vmcore after a crash:
*(struct btrfs_encoded_read_private *)0xffff88815626eec8 = {
.wait = (wait_queue_head_t){
.lock = (spinlock_t){
.rlock = (struct raw_spinlock){
.raw_lock = (arch_spinlock_t){
.val = (atomic_t){
.counter = (int)-2005885696,
},
.locked = (u8)0,
.pending = (u8)157,
.locked_pending = (u16)40192,
.tail = (u16)34928,
},
.magic = (unsigned int)536325682,
.owner_cpu = (unsigned int)29,
.owner = (void *)__SCT__tp_func_btrfs_transaction_commit+0x0 = 0x0,
.dep_map = (struct lockdep_map){
.key = (struct lock_class_key *)0xffff8881575a3b6c,
.class_cache = (struct lock_class *[2]){ 0xffff8882a71985c0, 0xffffea00066f5d40 },
.name = (const char *)0xffff88815626f100 = "",
.wait_type_outer = (u8)37,
.wait_type_inner = (u8)178,
.lock_type = (u8)154,
},
},
.__padding = (u8 [24]){ 0, 157, 112, 136, 50, 174, 247, 31, 29 },
.dep_map = (struct lockdep_map){
.key = (struct lock_class_key *)0xffff8881575a3b6c,
.class_cache = (struct lock_class *[2]){ 0xffff8882a71985c0, 0xffffea00066f5d40 },
.name = (const char *)0xffff88815626f100 = "",
.wait_type_outer = (u8)37,
.wait_type_inner = (u8)178,
.lock_type = (u8)154,
},
},
.head = (struct list_head){
.next = (struct list_head *)0x112cca,
.prev = (struct list_head *)0x47,
},
},
.pending = (atomic_t){
.counter = (int)-1491499288,
},
.status = (blk_status_t)130,
}
Here we can see several indicators of in-memory data corruption, e.g. the
large negative atomic values of ->pending or
->wait->lock->rlock->raw_lock->val, as well as the bogus spinlock magic
0x1ff7ae32 (decimal 536325682 above) instead of 0xdead4ead or the bogus
pointer values for ->wait->head.
To fix this, change atomic_dec_return() to atomic_dec_and_test() to fix the
corruption, as atomic_dec_return() is defined as two instructions on
x86_64, whereas atomic_dec_and_test() is defined as a single atomic
operation. This can lead to a situation where counter value is already
decremented but the if statement in btrfs_encoded_read_endio() is not
completely processed, i.e. the 0 test has not completed. If another thread
continues executing btrfs_encoded_read_regular_fill_pages() the
atomic_dec_return() there can see an already updated ->pending counter and
continues by freeing the private data. Continuing in the endio handler the
test for 0 succeeds and the wait_queue is woken up, resulting in a
use-after-free.
Reported-by: Shinichiro Kawasaki <shinichiro.kawasaki@xxxxxxx>
Suggested-by: Damien Le Moal <Damien.LeMoal@xxxxxxx>
Fixes: 1881fba89bd5 ("btrfs: add BTRFS_IOC_ENCODED_READ ioctl")
CC: stable@xxxxxxxxxxxxxxx # 6.1+
Reviewed-by: Filipe Manana <fdmanana@xxxxxxxx>
Reviewed-by: Qu Wenruo <wqu@xxxxxxxx>
Signed-off-by: Johannes Thumshirn <johannes.thumshirn@xxxxxxx>
Reviewed-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 857cbe9b07d28..d067db2619713 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -9126,7 +9126,7 @@ static void btrfs_encoded_read_endio(struct btrfs_bio *bbio)
*/
WRITE_ONCE(priv->status, bbio->bio.bi_status);
}
- if (!atomic_dec_return(&priv->pending))
+ if (atomic_dec_and_test(&priv->pending))
wake_up(&priv->wait);
bio_put(&bbio->bio);
}
