syzkaller has found reproducer for the following crash on ae64f9bd1d3621b5e60d7363bc20afb46aede215 git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/master compiler: gcc (GCC) 7.1.1 20170620 .config is attached Raw console output is attached. C reproducer is attached syzkaller reproducer is attached. See https://goo.gl/kgGztJ for information about syzkaller reproducers ====================================================== WARNING: possible circular locking dependency detected 4.15.0-rc2+ #206 Not tainted ------------------------------------------------------ syzkaller022699/3086 is trying to acquire lock: (&pipe->mutex/1){+.+.}, at: [<00000000698950dd>] __pipe_lock fs/pipe.c:88 [inline] (&pipe->mutex/1){+.+.}, at: [<00000000698950dd>] fifo_open+0x15c/0xa40 fs/pipe.c:916 but task is already holding lock: (&sig->cred_guard_mutex){+.+.}, at: [<0000000082fd15e8>] prepare_bprm_creds+0x53/0x110 fs/exec.c:1390 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (&sig->cred_guard_mutex){+.+.}: lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:4004 __mutex_lock_common kernel/locking/mutex.c:756 [inline] __mutex_lock+0x16f/0x1a80 kernel/locking/mutex.c:893 mutex_lock_killable_nested+0x16/0x20 kernel/locking/mutex.c:923 do_io_accounting+0x1c2/0xf50 fs/proc/base.c:2682 proc_tgid_io_accounting+0x22/0x30 fs/proc/base.c:2731 proc_single_show+0xf8/0x170 fs/proc/base.c:744 seq_read+0x385/0x13d0 fs/seq_file.c:234 __vfs_read+0xef/0xa00 fs/read_write.c:411 vfs_read+0x124/0x360 fs/read_write.c:447 SYSC_read fs/read_write.c:573 [inline] SyS_read+0xef/0x220 fs/read_write.c:566 entry_SYSCALL_64_fastpath+0x1f/0x96 -> #1 (&p->lock){+.+.}: lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:4004 __mutex_lock_common kernel/locking/mutex.c:756 [inline] __mutex_lock+0x16f/0x1a80 kernel/locking/mutex.c:893 mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908 seq_read+0xd5/0x13d0 fs/seq_file.c:165 do_loop_readv_writev fs/read_write.c:673 [inline] do_iter_read+0x3db/0x5b0 fs/read_write.c:897 vfs_readv+0x121/0x1c0 fs/read_write.c:959 kernel_readv fs/splice.c:361 [inline] default_file_splice_read+0x508/0xae0 fs/splice.c:416 do_splice_to+0x110/0x170 fs/splice.c:880 do_splice fs/splice.c:1173 [inline] SYSC_splice fs/splice.c:1402 [inline] SyS_splice+0x11a8/0x1630 fs/splice.c:1382 entry_SYSCALL_64_fastpath+0x1f/0x96 -> #0 (&pipe->mutex/1){+.+.}: check_prevs_add kernel/locking/lockdep.c:2031 [inline] validate_chain kernel/locking/lockdep.c:2473 [inline] __lock_acquire+0x3498/0x47f0 kernel/locking/lockdep.c:3500 lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:4004 __mutex_lock_common kernel/locking/mutex.c:756 [inline] __mutex_lock+0x16f/0x1a80 kernel/locking/mutex.c:893 mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908 __pipe_lock fs/pipe.c:88 [inline] fifo_open+0x15c/0xa40 fs/pipe.c:916 do_dentry_open+0x682/0xd70 fs/open.c:752 vfs_open+0x107/0x230 fs/open.c:866 do_last fs/namei.c:3379 [inline] path_openat+0x1157/0x3530 fs/namei.c:3519 do_filp_open+0x25b/0x3b0 fs/namei.c:3554 do_open_execat+0x1b9/0x5c0 fs/exec.c:849 do_execveat_common.isra.30+0x90c/0x23c0 fs/exec.c:1741 do_execve fs/exec.c:1848 [inline] SYSC_execve fs/exec.c:1929 [inline] SyS_execve+0x39/0x50 fs/exec.c:1924 do_syscall_64+0x26c/0x920 arch/x86/entry/common.c:285 return_from_SYSCALL_64+0x0/0x75 other info that might help us debug this: Chain exists of: &pipe->mutex/1 --> &p->lock --> &sig->cred_guard_mutex Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&sig->cred_guard_mutex); lock(&p->lock); lock(&sig->cred_guard_mutex); lock(&pipe->mutex/1); *** DEADLOCK *** 1 lock held by syzkaller022699/3086: #0: (&sig->cred_guard_mutex){+.+.}, at: [<0000000082fd15e8>] prepare_bprm_creds+0x53/0x110 fs/exec.c:1390 stack backtrace: CPU: 0 PID: 3086 Comm: syzkaller022699 Not tainted 4.15.0-rc2+ #206 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+0x194/0x257 lib/dump_stack.c:53 print_circular_bug+0x42d/0x610 kernel/locking/lockdep.c:1271 check_prev_add+0x666/0x15f0 kernel/locking/lockdep.c:1914 check_prevs_add kernel/locking/lockdep.c:2031 [inline] validate_chain kernel/locking/lockdep.c:2473 [inline] __lock_acquire+0x3498/0x47f0 kernel/locking/lockdep.c:3500 lock_acquire+0x1d5/0x580 kernel/locking/lockdep.c:4004 __mutex_lock_common kernel/locking/mutex.c:756 [inline] __mutex_lock+0x16f/0x1a80 kernel/locking/mutex.c:893 mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908 __pipe_lock fs/pipe.c:88 [inline] fifo_open+0x15c/0xa40 fs/pipe.c:916 do_dentry_open+0x682/0xd70 fs/open.c:752 vfs_open+0x107/0x230 fs/open.c:866 do_last fs/namei.c:3379 [inline] path_openat+0x1157/0x3530 fs/namei.c:3519 do_filp_open+0x25b/0x3b0 fs/namei.c:3554 do_open_execat+0x1b9/0x5c0 fs/exec.c:849 do_execveat_common.isra.30+0x90c/0x23c0 fs/exec.c:1741 do_execve fs/exec.c:1848 [inline] SYSC_execve fs/exec.c:1929 [inline] SyS_execve+0x39/0x50 fs/exec.c:1924 do_syscall_64+0x26c/0x920 arch/x86/entry/common.c:285 entry_SYSCALL64_slow_path+0x25/0x25 RIP: 0033:0x440219 RSP: 002b:00007ffd9e4890b8 EFLAGS: 00000217 ORIG_RAX: 000000000000003b RAX: ffffffffffffffda RBX: 0030656c69662f2e RCX: 0000000000440219 RDX: 0000000020324ff0 RSI: 0000000020a7bfc8 RDI: 0000000020f8aff8 RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000001 R10: 0000000000000001 R11: 0000000000000217 R12: 0000000000401ae0 R13: 0000000000401b70 R14: 0000000000000000 R15: 0000000000000000