[PATCH 4.19 053/105] btrfs: free btrfs_path before copying root refs to userspace

Greg Kroah-Hartman
2022-12-05T19:20:10Z

From: Josef Bacik <josef@toxicpanda.com>

commit b740d806166979488e798e41743aaec051f2443f upstream.

Syzbot reported the following lockdep splat

======================================================
WARNING: possible circular locking dependency detected
6.0.0-rc7-syzkaller-18095-gbbed346d5a96 #0 Not tainted
------------------------------------------------------
syz-executor307/3029 is trying to acquire lock:
ffff0000c02525d8 (&mm->mmap_lock){++++}-{3:3}, at: __might_fault+0x54/0xb4 mm/memory.c:5576

but task is already holding lock:
ffff0000c958a608 (btrfs-root-00){++++}-{3:3}, at: __btrfs_tree_read_lock fs/btrfs/locking.c:134 [inline]
ffff0000c958a608 (btrfs-root-00){++++}-{3:3}, at: btrfs_tree_read_lock fs/btrfs/locking.c:140 [inline]
ffff0000c958a608 (btrfs-root-00){++++}-{3:3}, at: btrfs_read_lock_root_node+0x13c/0x1c0 fs/btrfs/locking.c:279

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #3 (btrfs-root-00){++++}-{3:3}:
down_read_nested+0x64/0x84 kernel/locking/rwsem.c:1624
__btrfs_tree_read_lock fs/btrfs/locking.c:134 [inline]
btrfs_tree_read_lock fs/btrfs/locking.c:140 [inline]
btrfs_read_lock_root_node+0x13c/0x1c0 fs/btrfs/locking.c:279
btrfs_search_slot_get_root+0x74/0x338 fs/btrfs/ctree.c:1637
btrfs_search_slot+0x1b0/0xfd8 fs/btrfs/ctree.c:1944
btrfs_update_root+0x6c/0x5a0 fs/btrfs/root-tree.c:132
commit_fs_roots+0x1f0/0x33c fs/btrfs/transaction.c:1459
btrfs_commit_transaction+0x89c/0x12d8 fs/btrfs/transaction.c:2343
flush_space+0x66c/0x738 fs/btrfs/space-info.c:786
btrfs_async_reclaim_metadata_space+0x43c/0x4e0 fs/btrfs/space-info.c:1059
process_one_work+0x2d8/0x504 kernel/workqueue.c:2289
worker_thread+0x340/0x610 kernel/workqueue.c:2436
kthread+0x12c/0x158 kernel/kthread.c:376
ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:860

-> #2 (&fs_info->reloc_mutex){+.+.}-{3:3}:
__mutex_lock_common+0xd4/0xca8 kernel/locking/mutex.c:603
__mutex_lock kernel/locking/mutex.c:747 [inline]
mutex_lock_nested+0x38/0x44 kernel/locking/mutex.c:799
btrfs_record_root_in_trans fs/btrfs/transaction.c:516 [inline]
start_transaction+0x248/0x944 fs/btrfs/transaction.c:752
btrfs_start_transaction+0x34/0x44 fs/btrfs/transaction.c:781
btrfs_create_common+0xf0/0x1b4 fs/btrfs/inode.c:6651
btrfs_create+0x8c/0xb0 fs/btrfs/inode.c:6697
lookup_open fs/namei.c:3413 [inline]
open_last_lookups fs/namei.c:3481 [inline]
path_openat+0x804/0x11c4 fs/namei.c:3688
do_filp_open+0xdc/0x1b8 fs/namei.c:3718
do_sys_openat2+0xb8/0x22c fs/open.c:1313
do_sys_open fs/open.c:1329 [inline]
__do_sys_openat fs/open.c:1345 [inline]
__se_sys_openat fs/open.c:1340 [inline]
__arm64_sys_openat+0xb0/0xe0 fs/open.c:1340
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall arch/arm64/kernel/syscall.c:52 [inline]
el0_svc_common+0x138/0x220 arch/arm64/kernel/syscall.c:142
do_el0_svc+0x48/0x164 arch/arm64/kernel/syscall.c:206
el0_svc+0x58/0x150 arch/arm64/kernel/entry-common.c:636
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:654
el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:581

-> #1 (sb_internal#2){.+.+}-{0:0}:
percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
__sb_start_write include/linux/fs.h:1826 [inline]
sb_start_intwrite include/linux/fs.h:1948 [inline]
start_transaction+0x360/0x944 fs/btrfs/transaction.c:683
btrfs_join_transaction+0x30/0x40 fs/btrfs/transaction.c:795
btrfs_dirty_inode+0x50/0x140 fs/btrfs/inode.c:6103
btrfs_update_time+0x1c0/0x1e8 fs/btrfs/inode.c:6145
inode_update_time fs/inode.c:1872 [inline]
touch_atime+0x1f0/0x4a8 fs/inode.c:1945
file_accessed include/linux/fs.h:2516 [inline]
btrfs_file_mmap+0x50/0x88 fs/btrfs/file.c:2407
call_mmap include/linux/fs.h:2192 [inline]
mmap_region+0x7fc/0xc14 mm/mmap.c:1752
do_mmap+0x644/0x97c mm/mmap.c:1540
vm_mmap_pgoff+0xe8/0x1d0 mm/util.c:552
ksys_mmap_pgoff+0x1cc/0x278 mm/mmap.c:1586
__do_sys_mmap arch/arm64/kernel/sys.c:28 [inline]
__se_sys_mmap arch/arm64/kernel/sys.c:21 [inline]
__arm64_sys_mmap+0x58/0x6c arch/arm64/kernel/sys.c:21
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall arch/arm64/kernel/syscall.c:52 [inline]
el0_svc_common+0x138/0x220 arch/arm64/kernel/syscall.c:142
do_el0_svc+0x48/0x164 arch/arm64/kernel/syscall.c:206
el0_svc+0x58/0x150 arch/arm64/kernel/entry-common.c:636
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:654
el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:581

-> #0 (&mm->mmap_lock){++++}-{3:3}:
check_prev_add kernel/locking/lockdep.c:3095 [inline]
check_prevs_add kernel/locking/lockdep.c:3214 [inline]
validate_chain kernel/locking/lockdep.c:3829 [inline]
__lock_acquire+0x1530/0x30a4 kernel/locking/lockdep.c:5053
lock_acquire+0x100/0x1f8 kernel/locking/lockdep.c:5666
__might_fault+0x7c/0xb4 mm/memory.c:5577
_copy_to_user include/linux/uaccess.h:134 [inline]
copy_to_user include/linux/uaccess.h:160 [inline]
btrfs_ioctl_get_subvol_rootref+0x3a8/0x4bc fs/btrfs/ioctl.c:3203
btrfs_ioctl+0xa08/0xa64 fs/btrfs/ioctl.c:5556
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:870 [inline]
__se_sys_ioctl fs/ioctl.c:856 [inline]
__arm64_sys_ioctl+0xd0/0x140 fs/ioctl.c:856
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall arch/arm64/kernel/syscall.c:52 [inline]
el0_svc_common+0x138/0x220 arch/arm64/kernel/syscall.c:142
do_el0_svc+0x48/0x164 arch/arm64/kernel/syscall.c:206
el0_svc+0x58/0x150 arch/arm64/kernel/entry-common.c:636
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:654
el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:581

other info that might help us debug this:

Chain exists of:
&mm->mmap_lock --> &fs_info->reloc_mutex --> btrfs-root-00

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(btrfs-root-00);
lock(&fs_info->reloc_mutex);
lock(btrfs-root-00);
lock(&mm->mmap_lock);

*** DEADLOCK ***

1 lock held by syz-executor307/3029:
#0: ffff0000c958a608 (btrfs-root-00){++++}-{3:3}, at: __btrfs_tree_read_lock fs/btrfs/locking.c:134 [inline]
#0: ffff0000c958a608 (btrfs-root-00){++++}-{3:3}, at: btrfs_tree_read_lock fs/btrfs/locking.c:140 [inline]
#0: ffff0000c958a608 (btrfs-root-00){++++}-{3:3}, at: btrfs_read_lock_root_node+0x13c/0x1c0 fs/btrfs/locking.c:279

stack backtrace:
CPU: 0 PID: 3029 Comm: syz-executor307 Not tainted 6.0.0-rc7-syzkaller-18095-gbbed346d5a96 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/30/2022
Call trace:
dump_backtrace+0x1c4/0x1f0 arch/arm64/kernel/stacktrace.c:156
show_stack+0x2c/0x54 arch/arm64/kernel/stacktrace.c:163
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x104/0x16c lib/dump_stack.c:106
dump_stack+0x1c/0x58 lib/dump_stack.c:113
print_circular_bug+0x2c4/0x2c8 kernel/locking/lockdep.c:2053
check_noncircular+0x14c/0x154 kernel/locking/lockdep.c:2175
check_prev_add kernel/locking/lockdep.c:3095 [inline]
check_prevs_add kernel/locking/lockdep.c:3214 [inline]
validate_chain kernel/locking/lockdep.c:3829 [inline]
__lock_acquire+0x1530/0x30a4 kernel/locking/lockdep.c:5053
lock_acquire+0x100/0x1f8 kernel/locking/lockdep.c:5666
__might_fault+0x7c/0xb4 mm/memory.c:5577
_copy_to_user include/linux/uaccess.h:134 [inline]
copy_to_user include/linux/uaccess.h:160 [inline]
btrfs_ioctl_get_subvol_rootref+0x3a8/0x4bc fs/btrfs/ioctl.c:3203
btrfs_ioctl+0xa08/0xa64 fs/btrfs/ioctl.c:5556
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:870 [inline]
__se_sys_ioctl fs/ioctl.c:856 [inline]
__arm64_sys_ioctl+0xd0/0x140 fs/ioctl.c:856
__invoke_syscall arch/arm64/kernel/syscall.c:38 [inline]
invoke_syscall arch/arm64/kernel/syscall.c:52 [inline]
el0_svc_common+0x138/0x220 arch/arm64/kernel/syscall.c:142
do_el0_svc+0x48/0x164 arch/arm64/kernel/syscall.c:206
el0_svc+0x58/0x150 arch/arm64/kernel/entry-common.c:636
el0t_64_sync_handler+0x84/0xf0 arch/arm64/kernel/entry-common.c:654
el0t_64_sync+0x18c/0x190 arch/arm64/kernel/entry.S:581

We do generally the right thing here, copying the references into a
temporary buffer, however we are still holding the path when we do
copy_to_user from the temporary buffer. Fix this by freeing the path
before we copy to user space.

Reported-by: syzbot+4ef9e52e464c6ff47d9d@syzkaller.appspotmail.com
CC: stable@vger.kernel.org # 4.19+
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
fs/btrfs/ioctl.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2849,6 +2849,8 @@ static int btrfs_ioctl_get_subvol_rootre
}

out:
+ btrfs_free_path(path);
+
if (!ret || ret == -EOVERFLOW) {
rootrefs->num_items = found;
/* update min_treeid for next search */
@@ -2860,7 +2862,6 @@ out:
}

kfree(rootrefs);
- btrfs_free_path(path);

return ret;
}