Linux kernel crash report:
======================================================
WARNING: possible circular locking dependency detected
5.1.0-rc2 #36 Not tainted
------------------------------------------------------
syz-executor313/7589 is trying to acquire lock:
00000000c33e27a0 (&p->lock){+.+.}, at: seq_read+0x71/0x1130 fs/seq_file.c:161

but task is already holding lock:
00000000c9a9488b (&pipe->mutex/1){+.+.}, at: pipe_lock_nested fs/pipe.c:62 [inline]
00000000c9a9488b (&pipe->mutex/1){+.+.}, at: pipe_lock+0x6e/0x80 fs/pipe.c:70

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #2 (&pipe->mutex/1){+.+.}:
       lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:4211
       __mutex_lock_common kernel/locking/mutex.c:925 [inline]
       __mutex_lock+0xf7/0x1310 kernel/locking/mutex.c:1072
       mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1087
       __pipe_lock fs/pipe.c:83 [inline]
       fifo_open+0x159/0xb00 fs/pipe.c:930
       do_dentry_open+0x488/0x1160 fs/open.c:771
       vfs_open+0xa0/0xd0 fs/open.c:880
       do_last fs/namei.c:3416 [inline]
       path_openat+0x10e9/0x46e0 fs/namei.c:3533
       do_filp_open+0x1a1/0x280 fs/namei.c:3563
       do_open_execat+0x137/0x690 fs/exec.c:856
       __do_execve_file.isra.0+0x178d/0x23f0 fs/exec.c:1758
       do_execveat_common fs/exec.c:1865 [inline]
       do_execve fs/exec.c:1882 [inline]
       __do_sys_execve fs/exec.c:1958 [inline]
       __se_sys_execve fs/exec.c:1953 [inline]
       __x64_sys_execve+0x8f/0xc0 fs/exec.c:1953
       do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
       entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #1 (&sig->cred_guard_mutex){+.+.}:
       lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:4211
       __mutex_lock_common kernel/locking/mutex.c:925 [inline]
       __mutex_lock+0xf7/0x1310 kernel/locking/mutex.c:1072
       mutex_lock_killable_nested+0x16/0x20 kernel/locking/mutex.c:1102
       lock_trace+0x4a/0xe0 fs/proc/base.c:388
       proc_pid_syscall+0x98/0x250 fs/proc/base.c:623
       proc_single_show+0xf6/0x170 fs/proc/base.c:743
       seq_read+0x4db/0x1130 fs/seq_file.c:229
       do_loop_readv_writev fs/read_write.c:700 [inline]
       do_loop_readv_writev fs/read_write.c:687 [inline]
       do_iter_read+0x4a9/0x660 fs/read_write.c:921
       vfs_readv+0xf0/0x160 fs/read_write.c:983
       kernel_readv fs/splice.c:358 [inline]
       default_file_splice_read+0x475/0x890 fs/splice.c:413
       do_splice_to+0x12a/0x190 fs/splice.c:876
       splice_direct_to_actor+0x2d2/0x970 fs/splice.c:953
       do_splice_direct+0x1da/0x2a0 fs/splice.c:1062
       do_sendfile+0x597/0xd00 fs/read_write.c:1442
       __do_sys_sendfile64 fs/read_write.c:1503 [inline]
       __se_sys_sendfile64 fs/read_write.c:1489 [inline]
       __x64_sys_sendfile64+0x1dd/0x220 fs/read_write.c:1489
       do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
       entry_SYSCALL_64_after_hwframe+0x49/0xbe

-> #0 (&p->lock){+.+.}:
       check_prevs_add kernel/locking/lockdep.c:2333 [inline]
       validate_chain kernel/locking/lockdep.c:2714 [inline]
       __lock_acquire+0x239c/0x3fb0 kernel/locking/lockdep.c:3701
       lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:4211
       __mutex_lock_common kernel/locking/mutex.c:925 [inline]
       __mutex_lock+0xf7/0x1310 kernel/locking/mutex.c:1072
       mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1087
       seq_read+0x71/0x1130 fs/seq_file.c:161
       proc_reg_read+0x1fe/0x2c0 fs/proc/inode.c:227
       do_loop_readv_writev fs/read_write.c:700 [inline]
       do_loop_readv_writev fs/read_write.c:687 [inline]
       do_iter_read+0x4a9/0x660 fs/read_write.c:921
       vfs_readv+0xf0/0x160 fs/read_write.c:983
       kernel_readv fs/splice.c:358 [inline]
       default_file_splice_read+0x475/0x890 fs/splice.c:413
       do_splice_to+0x12a/0x190 fs/splice.c:876
       do_splice+0x10a9/0x13c0 fs/splice.c:1183
       __do_sys_splice fs/splice.c:1424 [inline]
       __se_sys_splice fs/splice.c:1404 [inline]
       __x64_sys_splice+0x2c6/0x330 fs/splice.c:1404
       do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
       entry_SYSCALL_64_after_hwframe+0x49/0xbe

other info that might help us debug this:

Chain exists of:
  &p->lock --> &sig->cred_guard_mutex --> &pipe->mutex/1

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&pipe->mutex/1);
                               lock(&sig->cred_guard_mutex);
                               lock(&pipe->mutex/1);
  lock(&p->lock);

 *** DEADLOCK ***

1 lock held by syz-executor313/7589:
 #0: 00000000c9a9488b (&pipe->mutex/1){+.+.}, at: pipe_lock_nested fs/pipe.c:62 [inline]
 #0: 00000000c9a9488b (&pipe->mutex/1){+.+.}, at: pipe_lock+0x6e/0x80 fs/pipe.c:70

stack backtrace:
CPU: 0 PID: 7589 Comm: syz-executor313 Not tainted 5.1.0-rc2 #36
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+0x172/0x1f0 lib/dump_stack.c:113
 print_circular_bug.isra.0.cold+0x1cc/0x28f kernel/locking/lockdep.c:1571
 check_prev_add.constprop.0+0xf11/0x23c0 kernel/locking/lockdep.c:2220
 check_prevs_add kernel/locking/lockdep.c:2333 [inline]
 validate_chain kernel/locking/lockdep.c:2714 [inline]
 __lock_acquire+0x239c/0x3fb0 kernel/locking/lockdep.c:3701
 lock_acquire+0x16f/0x3f0 kernel/locking/lockdep.c:4211
 __mutex_lock_common kernel/locking/mutex.c:925 [inline]
 __mutex_lock+0xf7/0x1310 kernel/locking/mutex.c:1072
 mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:1087
 seq_read+0x71/0x1130 fs/seq_file.c:161
 proc_reg_read+0x1fe/0x2c0 fs/proc/inode.c:227
 do_loop_readv_writev fs/read_write.c:700 [inline]
 do_loop_readv_writev fs/read_write.c:687 [inline]
 do_iter_read+0x4a9/0x660 fs/read_write.c:921
 vfs_readv+0xf0/0x160 fs/read_write.c:983
 kernel_readv fs/splice.c:358 [inline]
 default_file_splice_read+0x475/0x890 fs/splice.c:413
 do_splice_to+0x12a/0x190 fs/splice.c:876
 do_splice+0x10a9/0x13c0 fs/splice.c:1183
 __do_sys_splice fs/splice.c:1424 [inline]
 __se_sys_splice fs/splice.c:1404 [inline]
 __x64_sys_splice+0x2c6/0x330 fs/splice.c:1404
 do_syscall_64+0x103/0x610 arch/x86/entry/common.c:290
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4459c9
Code: e8 3c ba 02 00 48 83 c4 18 c3 0f 1f 80 00 00 00 00 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 8b 12 fc ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f5743732d88 EFLAGS: 00000246 ORIG_RAX: 0000000000000113
RAX: ffffffffffffffda RBX: 00000000006dac68 RCX: 00000000004459c9
RDX: 0000000000000006 RSI: 0000000000000000 RDI: 0000000000000007
RBP: 00000000006dac60 R08: 0000000000000002 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00000000006dac6c
R13: 00000000004ae050 R14: 0000000000000027 R15: 0000000000000872


Fix patch:
diff --git a/fs/open.c b/fs/open.c
index 0285ce7dbd51..f1c2f855fd43 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -733,6 +733,12 @@ static int do_dentry_open(struct file *f,
 		return 0;
 	}
 
+	/* Any file opened for execve()/uselib() has to be a regular file. */
+	if (unlikely(f->f_flags & FMODE_EXEC && !S_ISREG(inode->i_mode))) {
+		error = -EACCES;
+		goto cleanup_file;
+	}
+
 	if (f->f_mode & FMODE_WRITE && !special_file(inode->i_mode)) {
 		error = get_write_access(inode);
 		if (unlikely(error))