Re: [syzbot] [keyrings?] [lsm?] [ext4?] possible deadlock in keyring_clear (2)

syzbot
2024-09-27T14:15:03Z

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
possible deadlock in keyring_clear

======================================================
WARNING: possible circular locking dependency detected
6.11.0-syzkaller-11558-g075dbe9f6e3c-dirty #0 Not tainted
------------------------------------------------------
kswapd0/79 is trying to acquire lock:
ffff88804acb05d8 (&type->lock_class){+.+.}-{3:3}, at: keyring_clear+0xb2/0x350 security/keys/keyring.c:1655

but task is already holding lock:
ffffffff8ea37100 (fs_reclaim){+.+.}-{0:0}, at: balance_pgdat mm/vmscan.c:6844 [inline]
ffffffff8ea37100 (fs_reclaim){+.+.}-{0:0}, at: kswapd+0xbf1/0x3700 mm/vmscan.c:7226

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (fs_reclaim){+.+.}-{0:0}:
lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5822
__fs_reclaim_acquire mm/page_alloc.c:3834 [inline]
fs_reclaim_acquire+0x88/0x140 mm/page_alloc.c:3848
might_alloc include/linux/sched/mm.h:327 [inline]
slab_pre_alloc_hook mm/slub.c:4037 [inline]
slab_alloc_node mm/slub.c:4115 [inline]
__kmalloc_cache_noprof+0x3d/0x2c0 mm/slub.c:4291
kmalloc_noprof include/linux/slab.h:878 [inline]
kzalloc_noprof include/linux/slab.h:1014 [inline]
assoc_array_clear+0x78/0x1a0 lib/assoc_array.c:1284
keyring_clear+0xc5/0x350 security/keys/keyring.c:1657
fscrypt_put_master_key+0xc8/0x190 fs/crypto/keyring.c:79
fscrypt_initiate_key_removal fs/crypto/keyring.c:137 [inline]
fscrypt_destroy_keyring+0x1a7/0x2d0 fs/crypto/keyring.c:259
generic_shutdown_super+0x14a/0x2d0 fs/super.c:648
kill_block_super+0x44/0x90 fs/super.c:1696
ext4_kill_sb+0x68/0xa0 fs/ext4/super.c:7320
deactivate_locked_super+0xc4/0x130 fs/super.c:473
cleanup_mnt+0x41f/0x4b0 fs/namespace.c:1373
task_work_run+0x24f/0x310 kernel/task_work.c:228
resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
exit_to_user_mode_loop kernel/entry/common.c:114 [inline]
exit_to_user_mode_prepare include/linux/entry-common.h:328 [inline]
__syscall_exit_to_user_mode_work kernel/entry/common.c:207 [inline]
syscall_exit_to_user_mode+0x168/0x370 kernel/entry/common.c:218
do_syscall_64+0x100/0x230 arch/x86/entry/common.c:89
entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&type->lock_class){+.+.}-{3:3}:
check_prev_add kernel/locking/lockdep.c:3158 [inline]
check_prevs_add kernel/locking/lockdep.c:3277 [inline]
validate_chain+0x18ef/0x5920 kernel/locking/lockdep.c:3901
__lock_acquire+0x1384/0x2050 kernel/locking/lockdep.c:5199
lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5822
down_write+0x99/0x220 kernel/locking/rwsem.c:1579
keyring_clear+0xb2/0x350 security/keys/keyring.c:1655
fscrypt_put_master_key+0xc8/0x190 fs/crypto/keyring.c:79
put_crypt_info+0x275/0x320 fs/crypto/keysetup.c:548
fscrypt_put_encryption_info+0x40/0x60 fs/crypto/keysetup.c:753
ext4_clear_inode+0x15b/0x1c0 fs/ext4/super.c:1525
ext4_evict_inode+0xabc/0xf50 fs/ext4/inode.c:323
evict+0x4e8/0x9b0 fs/inode.c:723
__dentry_kill+0x20d/0x630 fs/dcache.c:615
shrink_kill+0xa9/0x2c0 fs/dcache.c:1060
shrink_dentry_list+0x2c0/0x5b0 fs/dcache.c:1087
prune_dcache_sb+0x10f/0x180 fs/dcache.c:1168
super_cache_scan+0x34f/0x4b0 fs/super.c:221
do_shrink_slab+0x701/0x1160 mm/shrinker.c:435
shrink_slab_memcg mm/shrinker.c:548 [inline]
shrink_slab+0x878/0x14d0 mm/shrinker.c:626
shrink_one+0x43b/0x850 mm/vmscan.c:4818
shrink_many mm/vmscan.c:4879 [inline]
lru_gen_shrink_node mm/vmscan.c:4957 [inline]
shrink_node+0x3799/0x3de0 mm/vmscan.c:5937
kswapd_shrink_node mm/vmscan.c:6765 [inline]
balance_pgdat mm/vmscan.c:6957 [inline]
kswapd+0x1ca3/0x3700 mm/vmscan.c:7226
kthread+0x2f0/0x390 kernel/kthread.c:389
ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

other info that might help us debug this:

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(fs_reclaim);
lock(&type->lock_class);
lock(fs_reclaim);
lock(&type->lock_class);

*** DEADLOCK ***

2 locks held by kswapd0/79:
#0: ffffffff8ea37100 (fs_reclaim){+.+.}-{0:0}, at: balance_pgdat mm/vmscan.c:6844 [inline]
#0: ffffffff8ea37100 (fs_reclaim){+.+.}-{0:0}, at: kswapd+0xbf1/0x3700 mm/vmscan.c:7226
#1: ffff8880007640e0 (&type->s_umount_key#32){++++}-{3:3}, at: super_trylock_shared fs/super.c:562 [inline]
#1: ffff8880007640e0 (&type->s_umount_key#32){++++}-{3:3}, at: super_cache_scan+0x94/0x4b0 fs/super.c:196

stack backtrace:
CPU: 0 UID: 0 PID: 79 Comm: kswapd0 Not tainted 6.11.0-syzkaller-11558-g075dbe9f6e3c-dirty #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
print_circular_bug+0x13a/0x1b0 kernel/locking/lockdep.c:2074
check_noncircular+0x36a/0x4a0 kernel/locking/lockdep.c:2203
check_prev_add kernel/locking/lockdep.c:3158 [inline]
check_prevs_add kernel/locking/lockdep.c:3277 [inline]
validate_chain+0x18ef/0x5920 kernel/locking/lockdep.c:3901
__lock_acquire+0x1384/0x2050 kernel/locking/lockdep.c:5199
lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5822
down_write+0x99/0x220 kernel/locking/rwsem.c:1579
keyring_clear+0xb2/0x350 security/keys/keyring.c:1655
fscrypt_put_master_key+0xc8/0x190 fs/crypto/keyring.c:79
put_crypt_info+0x275/0x320 fs/crypto/keysetup.c:548
fscrypt_put_encryption_info+0x40/0x60 fs/crypto/keysetup.c:753
ext4_clear_inode+0x15b/0x1c0 fs/ext4/super.c:1525
ext4_evict_inode+0xabc/0xf50 fs/ext4/inode.c:323
evict+0x4e8/0x9b0 fs/inode.c:723
__dentry_kill+0x20d/0x630 fs/dcache.c:615
shrink_kill+0xa9/0x2c0 fs/dcache.c:1060
shrink_dentry_list+0x2c0/0x5b0 fs/dcache.c:1087
prune_dcache_sb+0x10f/0x180 fs/dcache.c:1168
super_cache_scan+0x34f/0x4b0 fs/super.c:221
do_shrink_slab+0x701/0x1160 mm/shrinker.c:435
shrink_slab_memcg mm/shrinker.c:548 [inline]
shrink_slab+0x878/0x14d0 mm/shrinker.c:626
shrink_one+0x43b/0x850 mm/vmscan.c:4818
shrink_many mm/vmscan.c:4879 [inline]
lru_gen_shrink_node mm/vmscan.c:4957 [inline]
shrink_node+0x3799/0x3de0 mm/vmscan.c:5937
kswapd_shrink_node mm/vmscan.c:6765 [inline]
balance_pgdat mm/vmscan.c:6957 [inline]
kswapd+0x1ca3/0x3700 mm/vmscan.c:7226
kthread+0x2f0/0x390 kernel/kthread.c:389
ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
</TASK>

Tested on:

commit: 075dbe9f Merge tag 'soc-ep93xx-dt-6.12' of git://git.k..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=164306a9980000
kernel config: https://syzkaller.appspot.com/x/.config?x=f6cf7b6189844756
dashboard link: https://syzkaller.appspot.com/bug?extid=1b2d1134e0b675176a15
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
patch: https://syzkaller.appspot.com/x/patch.diff?x=16a4959f980000