possible deadlock in proc_pid

possible deadlock in proc_pid_syscall
Status: upstream: reported C repro on 2020/08/09 14:10
Reported-by: syzbot+fa8bc95e624704d42c25@syzkaller.appspotmail.com
First crash: 407d, last: 24d

similar bugs (3):
Kernel	Title	Repro	Count	Last	Reported	Patched	Status
linux-4.19	possible deadlock in proc_pid_syscall	syz	75	4d09h	453d	0/1	upstream: reported syz repro on 2020/06/24 12:57
upstream	possible deadlock in proc_pid_syscall (2)		2	378d	388d	21/22	fixed on 2021/03/10 01:48
upstream	possible deadlock in proc_pid_syscall		11	536d	674d	0/22	auto-closed as invalid on 2020/07/31 06:50

Sample crash report:

======================================================
WARNING: possible circular locking dependency detected
4.14.234-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor218/7975 is trying to acquire lock:
 (&sig->cred_guard_mutex){+.+.}, at: [<ffffffff81a097d7>] lock_trace fs/proc/base.c:407 [inline]
 (&sig->cred_guard_mutex){+.+.}, at: [<ffffffff81a097d7>] proc_pid_syscall+0xa7/0x2a0 fs/proc/base.c:639

but task is already holding lock:
 (&p->lock){+.+.}, at: [<ffffffff818e9f5a>] seq_read+0xba/0x1120 fs/seq_file.c:165

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (&p->lock){+.+.}:
       __mutex_lock_common kernel/locking/mutex.c:756 [inline]
       __mutex_lock+0xc4/0x1310 kernel/locking/mutex.c:893
       seq_read+0xba/0x1120 fs/seq_file.c:165
       do_loop_readv_writev fs/read_write.c:695 [inline]
       do_loop_readv_writev fs/read_write.c:682 [inline]
       do_iter_read+0x3eb/0x5b0 fs/read_write.c:919
       vfs_readv+0xc8/0x120 fs/read_write.c:981
       kernel_readv fs/splice.c:361 [inline]
       default_file_splice_read+0x418/0x910 fs/splice.c:416
       do_splice_to+0xfb/0x140 fs/splice.c:880
       splice_direct_to_actor+0x207/0x730 fs/splice.c:952
       do_splice_direct+0x164/0x210 fs/splice.c:1061
       do_sendfile+0x47f/0xb30 fs/read_write.c:1441
       SYSC_sendfile64 fs/read_write.c:1502 [inline]
       SyS_sendfile64+0xff/0x110 fs/read_write.c:1488
       do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
       entry_SYSCALL_64_after_hwframe+0x46/0xbb

-> #2 (sb_writers#3){.+.+}:
       percpu_down_read_preempt_disable include/linux/percpu-rwsem.h:36 [inline]
       percpu_down_read include/linux/percpu-rwsem.h:59 [inline]
       __sb_start_write+0x64/0x260 fs/super.c:1342
       sb_start_write include/linux/fs.h:1549 [inline]
       mnt_want_write+0x3a/0xb0 fs/namespace.c:386
       ovl_create_object+0x75/0x1d0 fs/overlayfs/dir.c:538
       lookup_open+0x77a/0x1750 fs/namei.c:3241
       do_last fs/namei.c:3334 [inline]
       path_openat+0xe08/0x2970 fs/namei.c:3569
       do_filp_open+0x179/0x3c0 fs/namei.c:3603
       do_sys_open+0x296/0x410 fs/open.c:1081
       do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
       entry_SYSCALL_64_after_hwframe+0x46/0xbb

-> #1 (&ovl_i_mutex_dir_key[depth]){++++}:
       down_read+0x36/0x80 kernel/locking/rwsem.c:24
       inode_lock_shared include/linux/fs.h:729 [inline]
       do_last fs/namei.c:3333 [inline]
       path_openat+0x149b/0x2970 fs/namei.c:3569
       do_filp_open+0x179/0x3c0 fs/namei.c:3603
       do_open_execat+0xd3/0x450 fs/exec.c:849
       do_execveat_common+0x711/0x1f30 fs/exec.c:1755
       do_execve fs/exec.c:1860 [inline]
       SYSC_execve fs/exec.c:1941 [inline]
       SyS_execve+0x3b/0x50 fs/exec.c:1936
       do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
       entry_SYSCALL_64_after_hwframe+0x46/0xbb

-> #0 (&sig->cred_guard_mutex){+.+.}:
       lock_acquire+0x170/0x3f0 kernel/locking/lockdep.c:3998
       __mutex_lock_common kernel/locking/mutex.c:756 [inline]
       __mutex_lock+0xc4/0x1310 kernel/locking/mutex.c:893
       lock_trace fs/proc/base.c:407 [inline]
       proc_pid_syscall+0xa7/0x2a0 fs/proc/base.c:639
       proc_single_show+0xe7/0x150 fs/proc/base.c:761
       seq_read+0x4cf/0x1120 fs/seq_file.c:237
       do_loop_readv_writev fs/read_write.c:695 [inline]
       do_loop_readv_writev fs/read_write.c:682 [inline]
       do_iter_read+0x3eb/0x5b0 fs/read_write.c:919
       vfs_readv+0xc8/0x120 fs/read_write.c:981
       kernel_readv fs/splice.c:361 [inline]
       default_file_splice_read+0x418/0x910 fs/splice.c:416
       do_splice_to+0xfb/0x140 fs/splice.c:880
       splice_direct_to_actor+0x207/0x730 fs/splice.c:952
       do_splice_direct+0x164/0x210 fs/splice.c:1061
       do_sendfile+0x47f/0xb30 fs/read_write.c:1441
       SYSC_sendfile64 fs/read_write.c:1502 [inline]
       SyS_sendfile64+0xff/0x110 fs/read_write.c:1488
       do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
       entry_SYSCALL_64_after_hwframe+0x46/0xbb

other info that might help us debug this:

Chain exists of:
  &sig->cred_guard_mutex --> sb_writers#3 --> &p->lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&p->lock);
                               lock(sb_writers#3);
                               lock(&p->lock);
  lock(&sig->cred_guard_mutex);

 *** DEADLOCK ***

2 locks held by syz-executor218/7975:
 #0:  (sb_writers#3){.+.+}, at: [<ffffffff8186badf>] file_start_write include/linux/fs.h:2712 [inline]
 #0:  (sb_writers#3){.+.+}, at: [<ffffffff8186badf>] do_sendfile+0x84f/0xb30 fs/read_write.c:1440
 #1:  (&p->lock){+.+.}, at: [<ffffffff818e9f5a>] seq_read+0xba/0x1120 fs/seq_file.c:165

stack backtrace:
CPU: 1 PID: 7975 Comm: syz-executor218 Not tainted 4.14.234-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:17 [inline]
 dump_stack+0x1b2/0x281 lib/dump_stack.c:58
 print_circular_bug.constprop.0.cold+0x2d7/0x41e kernel/locking/lockdep.c:1258
 check_prev_add kernel/locking/lockdep.c:1905 [inline]
 check_prevs_add kernel/locking/lockdep.c:2022 [inline]
 validate_chain kernel/locking/lockdep.c:2464 [inline]
 __lock_acquire+0x2e0e/0x3f20 kernel/locking/lockdep.c:3491
 lock_acquire+0x170/0x3f0 kernel/locking/lockdep.c:3998
 __mutex_lock_common kernel/locking/mutex.c:756 [inline]
 __mutex_lock+0xc4/0x1310 kernel/locking/mutex.c:893
 lock_trace fs/proc/base.c:407 [inline]
 proc_pid_syscall+0xa7/0x2a0 fs/proc/base.c:639
 proc_single_show+0xe7/0x150 fs/proc/base.c:761
 seq_read+0x4cf/0x1120 fs/seq_file.c:237
 do_loop_readv_writev fs/read_write.c:695 [inline]
 do_loop_readv_writev fs/read_write.c:682 [inline]
 do_iter_read+0x3eb/0x5b0 fs/read_write.c:919
 vfs_readv+0xc8/0x120 fs/read_write.c:981
 kernel_readv fs/splice.c:361 [inline]
 default_file_splice_read+0x418/0x910 fs/splice.c:416
 do_splice_to+0xfb/0x140 fs/splice.c:880
 splice_direct_to_actor+0x207/0x730 fs/splice.c:952
 do_splice_direct+0x164/0x210 fs/splice.c:1061
 do_sendfile+0x47f/0xb30 fs/read_write.c:1441
 SYSC_sendfile64 fs/read_write.c:1502 [inline]
 SyS_sendfile64+0xff/0x110 fs/read_write.c:1488
 do_syscall_64+0x1d5/0x640 arch/x86/entry/common.c:292
 entry_SYSCALL_64_after_hwframe+0x46/0xbb
RIP: 0033:0x43f239
RSP: 002b:00007ffcd4493098 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 0000000000400488 RCX: 000000000043f239
RDX: 0000000000000000 RSI: 0000000000000003 RDI: 0000000000000004
RBP: 00007ffcd44930a0 R08: 68742f636f72702f R09: 68742f636f72702f
R10: 0000000000000007 R11: 0000000000000246 R12: 00000000004031c0
R13: 0000000000000000 R14: 00000000004ad018 R15: 0000

Fix bisection attempts:
Manager	Time	Kernel	Commit	Syzkaller	Config	Log	Report	Syz repro	C repro
ci2-linux-4-14	2021/08/27 12:21	linux-4.14.y	35c4ba160ab6	858ea628	.config	log	report	syz	C
ci2-linux-4-14	2021/07/28 11:48	linux-4.14.y	ce4d1565392b	858ea628	.config	log	report	syz	C
ci2-linux-4-14	2021/06/28 11:16	linux-4.14.y	cfb41ef9deb1	858ea628	.config	log	report	syz	C
ci2-linux-4-14	2021/05/23 03:24	linux-4.14.y	96afcb20f36f	5ef9c291	.config	log	report	syz	C
ci2-linux-4-14	2021/02/24 08:34	linux-4.14.y	3242aa3a635c	5ef9c291	.config	log	report	syz	C
ci2-linux-4-14	2021/01/21 21:37	linux-4.14.y	2762b48e9611	5ef9c291	.config	log	report	syz	C
ci2-linux-4-14	2020/12/16 10:25	linux-4.14.y	3f2ecb86cb90	5ef9c291	.config	log	report	syz	C
ci2-linux-4-14	2020/11/04 08:01	linux-4.14.y	2b7915014161	5ef9c291	.config	log	report	syz	C

Crashes (17):
Manager	Time	Kernel	Commit	Syzkaller	Config	Log	Report	Syz repro	C repro	VM info	Title
ci2-linux-4-14	2021/05/29 10:39	linux-4.14.y	ad8397a84e1e	858ea628	.config	log	report	syz	C		possible deadlock in proc_pid_syscall
ci2-linux-4-14	2020/10/05 07:38	linux-4.14.y	cbfa1702aaf6	5ef9c291	.config	log	report	syz	C
ci2-linux-4-14	2021/04/23 02:53	linux-4.14.y	cf256fbcbe34	590921a5	.config	log	report			info	possible deadlock in proc_pid_syscall
ci2-linux-4-14	2021/04/12 23:19	linux-4.14.y	958e517f4e16	6a81331a	.config	log	report			info	possible deadlock in proc_pid_syscall
ci2-linux-4-14	2021/04/09 01:22	linux-4.14.y	0cc244011f40	6a81331a	.config	log	report			info	possible deadlock in proc_pid_syscall
ci2-linux-4-14	2021/04/07 16:02	linux-4.14.y	0cc244011f40	6a81331a	.config	log	report			info	possible deadlock in proc_pid_syscall
ci2-linux-4-14	2021/04/06 23:05	linux-4.14.y	bd634aa64163	6a81331a	.config	log	report			info	possible deadlock in proc_pid_syscall
ci2-linux-4-14	2021/04/02 10:38	linux-4.14.y	bd634aa64163	6a81331a	.config	log	report			info	possible deadlock in proc_pid_syscall
ci2-linux-4-14	2021/03/28 06:32	linux-4.14.y	670d6552eda8	a8529b82	.config	log	report			info	possible deadlock in proc_pid_syscall
ci2-linux-4-14	2021/03/24 12:25	linux-4.14.y	670d6552eda8	e613994b	.config	log	report			info	possible deadlock in proc_pid_syscall
ci2-linux-4-14	2021/01/24 19:30	linux-4.14.y	2d2791fce891	52e37319	.config	log	report			info	possible deadlock in proc_pid_syscall
ci2-linux-4-14	2020/12/22 20:34	linux-4.14.y	3f2ecb86cb90	04201c06	.config	log	report			info
ci2-linux-4-14	2020/11/16 09:55	linux-4.14.y	27ce4f2a6817	1bf9a662	.config	log	report			info
ci2-linux-4-14	2020/08/19 01:24	linux-4.14.y	14b58326976d	e1c29030	.config	log	report
ci2-linux-4-14	2020/08/15 09:50	linux-4.14.y	14b58326976d	5ce13532	.config	log	report
ci2-linux-4-14	2020/08/14 03:30	linux-4.14.y	14b58326976d	54ce1ed6	.config	log	report
ci2-linux-4-14	2020/08/09 14:09	linux-4.14.y	14b58326976d	70301872	.config	log	report