syzbot


possible deadlock in proc_pid_syscall (2)

Status: fixed on 2021/03/10 01:48
Reported-by: syzbot+db9cdf3dd1f64252c6ef@syzkaller.appspotmail.com
Fix commit: f7cfd871ae0c exec: Transform exec_update_mutex into a rw_semaphore 78af4dc949da perf: Break deadlock involving exec_update_mutex
First crash: 721d, last: 711d
similar bugs (3):
Kernel Title Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-4.19 possible deadlock in proc_pid_syscall syz error 152 4d05h 786d 0/1 upstream: reported syz repro on 2020/06/24 12:57
upstream possible deadlock in proc_pid_syscall 11 869d 1007d 0/23 auto-closed as invalid on 2020/07/31 06:50
linux-4.14 possible deadlock in proc_pid_syscall C 19 5d20h 740d 0/1 upstream: reported C repro on 2020/08/09 14:10

Sample crash report:
======================================================
WARNING: possible circular locking dependency detected
5.9.0-rc3-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor.2/31545 is trying to acquire lock:
ffff888036577788 (&sig->exec_update_mutex){+.+.}-{3:3}, at: lock_trace fs/proc/base.c:408 [inline]
ffff888036577788 (&sig->exec_update_mutex){+.+.}-{3:3}, at: proc_pid_syscall+0xaa/0x2b0 fs/proc/base.c:646

but task is already holding lock:
ffff888019a29370 (&p->lock){+.+.}-{3:3}, at: seq_lseek+0x58/0x3f0 fs/seq_file.c:294

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #3 (&p->lock){+.+.}-{3:3}:
       __mutex_lock_common kernel/locking/mutex.c:956 [inline]
       __mutex_lock+0x134/0x10e0 kernel/locking/mutex.c:1103
       seq_read+0x61/0x1070 fs/seq_file.c:155
       pde_read fs/proc/inode.c:306 [inline]
       proc_reg_read+0x221/0x300 fs/proc/inode.c:318
       do_loop_readv_writev fs/read_write.c:734 [inline]
       do_loop_readv_writev fs/read_write.c:721 [inline]
       do_iter_read+0x48e/0x6e0 fs/read_write.c:955
       vfs_readv+0xe5/0x150 fs/read_write.c:1073
       kernel_readv fs/splice.c:355 [inline]
       default_file_splice_read.constprop.0+0x4e6/0x9e0 fs/splice.c:412
       do_splice_to+0x137/0x170 fs/splice.c:871
       splice_direct_to_actor+0x307/0x980 fs/splice.c:950
       do_splice_direct+0x1b3/0x280 fs/splice.c:1059
       do_sendfile+0x55f/0xd40 fs/read_write.c:1540
       __do_sys_sendfile64 fs/read_write.c:1601 [inline]
       __se_sys_sendfile64 fs/read_write.c:1587 [inline]
       __x64_sys_sendfile64+0x1cc/0x210 fs/read_write.c:1587
       do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
       entry_SYSCALL_64_after_hwframe+0x44/0xa9

-> #2 (sb_writers#4){.+.+}-{0:0}:
       percpu_down_read include/linux/percpu-rwsem.h:51 [inline]
       __sb_start_write+0x234/0x470 fs/super.c:1672
       sb_start_write include/linux/fs.h:1643 [inline]
       mnt_want_write+0x3a/0xb0 fs/namespace.c:354
       ovl_create_object+0x96/0x290 fs/overlayfs/dir.c:625
       lookup_open.isra.0+0xf85/0x1350 fs/namei.c:3103
       open_last_lookups fs/namei.c:3177 [inline]
       path_openat+0x96d/0x2730 fs/namei.c:3365
       do_filp_open+0x17e/0x3c0 fs/namei.c:3395
       do_sys_openat2+0x16d/0x420 fs/open.c:1168
       do_sys_open fs/open.c:1184 [inline]
       __do_sys_open fs/open.c:1192 [inline]
       __se_sys_open fs/open.c:1188 [inline]
       __x64_sys_open+0x119/0x1c0 fs/open.c:1188
       do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
       entry_SYSCALL_64_after_hwframe+0x44/0xa9

-> #1 (&ovl_i_mutex_dir_key[depth]#2){++++}-{3:3}:
       down_read+0x96/0x420 kernel/locking/rwsem.c:1492
       inode_lock_shared include/linux/fs.h:789 [inline]
       lookup_slow fs/namei.c:1560 [inline]
       walk_component+0x409/0x6a0 fs/namei.c:1860
       lookup_last fs/namei.c:2309 [inline]
       path_lookupat+0x1ba/0x830 fs/namei.c:2333
       filename_lookup+0x19f/0x560 fs/namei.c:2366
       create_local_trace_uprobe+0x87/0x4e0 kernel/trace/trace_uprobe.c:1574
       perf_uprobe_init+0x132/0x210 kernel/trace/trace_event_perf.c:323
       perf_uprobe_event_init+0xff/0x1c0 kernel/events/core.c:9580
       perf_try_init_event+0x12a/0x560 kernel/events/core.c:10899
       perf_init_event kernel/events/core.c:10951 [inline]
       perf_event_alloc.part.0+0xdee/0x3770 kernel/events/core.c:11229
       perf_event_alloc kernel/events/core.c:11608 [inline]
       __do_sys_perf_event_open+0x72c/0x2cb0 kernel/events/core.c:11724
       do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
       entry_SYSCALL_64_after_hwframe+0x44/0xa9

-> #0 (&sig->exec_update_mutex){+.+.}-{3:3}:
       check_prev_add kernel/locking/lockdep.c:2496 [inline]
       check_prevs_add kernel/locking/lockdep.c:2601 [inline]
       validate_chain kernel/locking/lockdep.c:3218 [inline]
       __lock_acquire+0x29bb/0x5570 kernel/locking/lockdep.c:4426
       lock_acquire+0x1f3/0xae0 kernel/locking/lockdep.c:5006
       __mutex_lock_common kernel/locking/mutex.c:956 [inline]
       __mutex_lock+0x134/0x10e0 kernel/locking/mutex.c:1103
       lock_trace fs/proc/base.c:408 [inline]
       proc_pid_syscall+0xaa/0x2b0 fs/proc/base.c:646
       proc_single_show+0x116/0x1e0 fs/proc/base.c:775
       traverse.part.0+0xcf/0x590 fs/seq_file.c:107
       traverse fs/seq_file.c:97 [inline]
       seq_lseek+0x16f/0x3f0 fs/seq_file.c:304
       vfs_llseek fs/read_write.c:300 [inline]
       ksys_lseek+0x155/0x1b0 fs/read_write.c:313
       do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
       entry_SYSCALL_64_after_hwframe+0x44/0xa9

other info that might help us debug this:

Chain exists of:
  &sig->exec_update_mutex --> sb_writers#4 --> &p->lock

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&p->lock);
                               lock(sb_writers#4);
                               lock(&p->lock);
  lock(&sig->exec_update_mutex);

 *** DEADLOCK ***

2 locks held by syz-executor.2/31545:
 #0: ffff8880a872b130 (&f->f_pos_lock){+.+.}-{3:3}, at: __fdget_pos+0xe9/0x100 fs/file.c:930
 #1: ffff888019a29370 (&p->lock){+.+.}-{3:3}, at: seq_lseek+0x58/0x3f0 fs/seq_file.c:294

stack backtrace:
CPU: 0 PID: 31545 Comm: syz-executor.2 Not tainted 5.9.0-rc3-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x198/0x1fd lib/dump_stack.c:118
 check_noncircular+0x324/0x3e0 kernel/locking/lockdep.c:1827
 check_prev_add kernel/locking/lockdep.c:2496 [inline]
 check_prevs_add kernel/locking/lockdep.c:2601 [inline]
 validate_chain kernel/locking/lockdep.c:3218 [inline]
 __lock_acquire+0x29bb/0x5570 kernel/locking/lockdep.c:4426
 lock_acquire+0x1f3/0xae0 kernel/locking/lockdep.c:5006
 __mutex_lock_common kernel/locking/mutex.c:956 [inline]
 __mutex_lock+0x134/0x10e0 kernel/locking/mutex.c:1103
 lock_trace fs/proc/base.c:408 [inline]
 proc_pid_syscall+0xaa/0x2b0 fs/proc/base.c:646
 proc_single_show+0x116/0x1e0 fs/proc/base.c:775
 traverse.part.0+0xcf/0x590 fs/seq_file.c:107
 traverse fs/seq_file.c:97 [inline]
 seq_lseek+0x16f/0x3f0 fs/seq_file.c:304
 vfs_llseek fs/read_write.c:300 [inline]
 ksys_lseek+0x155/0x1b0 fs/read_write.c:313
 do_syscall_64+0x2d/0x70 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x44/0xa9
RIP: 0033:0x45d5b9
Code: 5d b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 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 0f 83 2b b4 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007fdf6806ec78 EFLAGS: 00000246 ORIG_RAX: 0000000000000008
RAX: ffffffffffffffda RBX: 0000000000020540 RCX: 000000000045d5b9
RDX: 0000000000000000 RSI: 0000000027aa958c RDI: 0000000000000005
RBP: 000000000118cf80 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 000000000118cf4c
R13: 00007fff65853a3f R14: 00007fdf6806f9c0 R15: 000000000118cf4c

Crashes (2):
Manager Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Title
ci-upstream-kasan-gce-root 2020/09/06 23:27 upstream dd9fb9bb3340 abf9ba4f .config log report
ci-upstream-kasan-gce-selinux-root 2020/08/28 03:41 upstream 15bc20c6af4c 816e0689 .config log report