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SubjectRe: [syzbot] possible deadlock in ovl_maybe_copy_up
From
syzbot has found a reproducer for the following issue on:

HEAD commit: 454c576c Add linux-next specific files for 20210401
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1616e07ed00000
kernel config: https://syzkaller.appspot.com/x/.config?x=920cc274cae812a5
dashboard link: https://syzkaller.appspot.com/bug?extid=c18f2f6a7b08c51e3025
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13da365ed00000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13ca9d16d00000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c18f2f6a7b08c51e3025@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
5.12.0-rc5-next-20210401-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor144/9166 is trying to acquire lock:
ffff888144cf0460 (sb_writers#5){.+.+}-{0:0}, at: ovl_maybe_copy_up+0x11f/0x190 fs/overlayfs/copy_up.c:995

but task is already holding lock:
ffff8880256d42c0 (&iint->mutex){+.+.}-{3:3}, at: process_measurement+0x3a8/0x17e0 security/integrity/ima/ima_main.c:253

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&iint->mutex){+.+.}-{3:3}:
__mutex_lock_common kernel/locking/mutex.c:949 [inline]
__mutex_lock+0x139/0x1120 kernel/locking/mutex.c:1096
process_measurement+0x3a8/0x17e0 security/integrity/ima/ima_main.c:253
ima_file_check+0xb9/0x100 security/integrity/ima/ima_main.c:499
do_open fs/namei.c:3361 [inline]
path_openat+0x15b5/0x27e0 fs/namei.c:3492
do_filp_open+0x17e/0x3c0 fs/namei.c:3519
do_sys_openat2+0x16d/0x420 fs/open.c:1187
do_sys_open fs/open.c:1203 [inline]
__do_sys_open fs/open.c:1211 [inline]
__se_sys_open fs/open.c:1207 [inline]
__x64_sys_open+0x119/0x1c0 fs/open.c:1207
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xae

-> #0 (sb_writers#5){.+.+}-{0:0}:
check_prev_add kernel/locking/lockdep.c:2938 [inline]
check_prevs_add kernel/locking/lockdep.c:3061 [inline]
validate_chain kernel/locking/lockdep.c:3676 [inline]
__lock_acquire+0x2a17/0x5230 kernel/locking/lockdep.c:4902
lock_acquire kernel/locking/lockdep.c:5512 [inline]
lock_acquire+0x1ab/0x740 kernel/locking/lockdep.c:5477
percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
__sb_start_write include/linux/fs.h:1758 [inline]
sb_start_write include/linux/fs.h:1828 [inline]
mnt_want_write+0x6e/0x3e0 fs/namespace.c:375
ovl_maybe_copy_up+0x11f/0x190 fs/overlayfs/copy_up.c:995
ovl_open+0xba/0x270 fs/overlayfs/file.c:149
do_dentry_open+0x4b9/0x11b0 fs/open.c:826
vfs_open fs/open.c:940 [inline]
dentry_open+0x132/0x1d0 fs/open.c:956
ima_calc_file_hash+0x2d2/0x4b0 security/integrity/ima/ima_crypto.c:557
ima_collect_measurement+0x4ca/0x570 security/integrity/ima/ima_api.c:252
process_measurement+0xd1c/0x17e0 security/integrity/ima/ima_main.c:330
ima_file_check+0xb9/0x100 security/integrity/ima/ima_main.c:499
do_open fs/namei.c:3361 [inline]
path_openat+0x15b5/0x27e0 fs/namei.c:3492
do_filp_open+0x17e/0x3c0 fs/namei.c:3519
do_sys_openat2+0x16d/0x420 fs/open.c:1187
do_sys_open fs/open.c:1203 [inline]
__do_sys_open fs/open.c:1211 [inline]
__se_sys_open fs/open.c:1207 [inline]
__x64_sys_open+0x119/0x1c0 fs/open.c:1207
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xae

other info that might help us debug this:

Possible unsafe locking scenario:

CPU0 CPU1
---- ----
lock(&iint->mutex);
lock(sb_writers#5);
lock(&iint->mutex);
lock(sb_writers#5);

*** DEADLOCK ***

1 lock held by syz-executor144/9166:
#0: ffff8880256d42c0 (&iint->mutex){+.+.}-{3:3}, at: process_measurement+0x3a8/0x17e0 security/integrity/ima/ima_main.c:253

stack backtrace:
CPU: 1 PID: 9166 Comm: syz-executor144 Not tainted 5.12.0-rc5-next-20210401-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:79 [inline]
dump_stack+0x141/0x1d7 lib/dump_stack.c:120
check_noncircular+0x25f/0x2e0 kernel/locking/lockdep.c:2129
check_prev_add kernel/locking/lockdep.c:2938 [inline]
check_prevs_add kernel/locking/lockdep.c:3061 [inline]
validate_chain kernel/locking/lockdep.c:3676 [inline]
__lock_acquire+0x2a17/0x5230 kernel/locking/lockdep.c:4902
lock_acquire kernel/locking/lockdep.c:5512 [inline]
lock_acquire+0x1ab/0x740 kernel/locking/lockdep.c:5477
percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
__sb_start_write include/linux/fs.h:1758 [inline]
sb_start_write include/linux/fs.h:1828 [inline]
mnt_want_write+0x6e/0x3e0 fs/namespace.c:375
ovl_maybe_copy_up+0x11f/0x190 fs/overlayfs/copy_up.c:995
ovl_open+0xba/0x270 fs/overlayfs/file.c:149
do_dentry_open+0x4b9/0x11b0 fs/open.c:826
vfs_open fs/open.c:940 [inline]
dentry_open+0x132/0x1d0 fs/open.c:956
ima_calc_file_hash+0x2d2/0x4b0 security/integrity/ima/ima_crypto.c:557
ima_collect_measurement+0x4ca/0x570 security/integrity/ima/ima_api.c:252
process_measurement+0xd1c/0x17e0 security/integrity/ima/ima_main.c:330
ima_file_check+0xb9/0x100 security/integrity/ima/ima_main.c:499
do_open fs/namei.c:3361 [inline]
path_openat+0x15b5/0x27e0 fs/namei.c:3492
do_filp_open+0x17e/0x3c0 fs/namei.c:3519
do_sys_openat2+0x16d/0x420 fs/open.c:1187
do_sys_open fs/open.c:1203 [inline]
__do_sys_open fs/open.c:1211 [inline]
__se_sys_open fs/open.c:1207 [inline]
__x64_sys_open+0x119/0x1c0 fs/open.c:1207
do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
entry_SYSCALL_64_after_hwframe+0x44/0xae
RIP: 0033:0x446109
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 41 15 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fe4412f12f8 EFLAGS: 00000246 ORIG_RAX: 0000000000000002
RAX: ffffffffffffffda RBX: 00000000004cb4c0 RCX: 0000000000446109
RDX: 0000000000000000 RSI: 0000000000000007 RDI: 00000000200001c0
RBP: 000000000049b06c R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 69662f7375622f2e
R13: 79706f636174656d R14: 0079616c7265766f R15: 00000000004cb4c8

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