On 22/7/24 07:57, syzbot wrote:
Hello,
syzbot found the following issue on:
I'm having trouble understanding this, you'll need to to better at the
explanation.
HEAD commit: d7e78951a8b8 Merge tag 'net-6.11-rc0' of git://git.kernel...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1642f7a5980000
kernel config: https://syzkaller.appspot.com/x/.config?x=2602dfd9213d734c
dashboard link: https://syzkaller.appspot.com/bug?extid=0d4e0978aa13f9e1db55
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
Unfortunately, I don't have any reproducer for this issue yet.
That might help since what the mounted file system is makes a difference.
Note that this notification is done to a specific user space process,
and there is only one for a
given autofs file system mount, and all other processes are read-only
within that autofs file
system. So I don't see how another process writing to a kernfs file can
play a part in this.
Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/cdd2c14644df/disk-d7e78951.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/7f9c9ab39b87/vmlinux-d7e78951.xz
kernel image: https://storage.googleapis.com/syzbot-assets/1fc3658770e2/bzImage-d7e78951.xz
IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+0d4e0978aa13f9e1db55@xxxxxxxxxxxxxxxxxxxxxxxxx
======================================================
WARNING: possible circular locking dependency detected
6.10.0-syzkaller-09703-gd7e78951a8b8 #0 Not tainted
------------------------------------------------------
syz.3.4748/19551 is trying to acquire lock:
ffff888059b0d940 (&sbi->pipe_mutex){+.+.}-{3:3}, at: autofs_write fs/autofs/waitq.c:55 [inline]
ffff888059b0d940 (&sbi->pipe_mutex){+.+.}-{3:3}, at: autofs_notify_daemon+0x71f/0xf80 fs/autofs/waitq.c:164
but task is already holding lock:
ffff8880758e7888 (&of->mutex){+.+.}-{3:3}, at: kernfs_fop_write_iter+0x1eb/0x500 fs/kernfs/file.c:325
which lock already depends on the new lock.
the existing dependency chain (in reverse order) is:
-> #2 (&of->mutex){+.+.}-{3:3}:
lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5759
__mutex_lock_common kernel/locking/mutex.c:608 [inline]
__mutex_lock+0x136/0xd70 kernel/locking/mutex.c:752
kernfs_fop_write_iter+0x1eb/0x500 fs/kernfs/file.c:325
iter_file_splice_write+0xbd7/0x14e0 fs/splice.c:743
do_splice_from fs/splice.c:941 [inline]
do_splice+0xd77/0x1900 fs/splice.c:1354
__do_splice fs/splice.c:1436 [inline]
__do_sys_splice fs/splice.c:1652 [inline]
__se_sys_splice+0x331/0x4a0 fs/splice.c:1634
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
Is it really possible for some process to try and take lock that
conflicts with a pipe owned
by a process that doesn't make calls into kernfs and will not open a
file in kernfs. This pipe
is opened against an autofs file system.
I don't understand the scenario you'll need to help me out with some
explanation of how such
an interaction can happen!
Ian
-> #1 (&pipe->mutex){+.+.}-{3:3}:
lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5759
__mutex_lock_common kernel/locking/mutex.c:608 [inline]
__mutex_lock+0x136/0xd70 kernel/locking/mutex.c:752
pipe_write+0x1c9/0x1a40 fs/pipe.c:455
__kernel_write_iter+0x47e/0x900 fs/read_write.c:523
__kernel_write+0x120/0x180 fs/read_write.c:543
autofs_write fs/autofs/waitq.c:57 [inline]
autofs_notify_daemon+0x732/0xf80 fs/autofs/waitq.c:164
autofs_wait+0x10b8/0x1b30 fs/autofs/waitq.c:426
autofs_do_expire_multi+0x659/0x950 fs/autofs/expire.c:590
autofs_root_ioctl+0x4c/0x60 fs/autofs/root.c:910
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:907 [inline]
__se_sys_ioctl+0xfc/0x170 fs/ioctl.c:893
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
-> #0 (&sbi->pipe_mutex){+.+.}-{3:3}:
check_prev_add kernel/locking/lockdep.c:3133 [inline]
check_prevs_add kernel/locking/lockdep.c:3252 [inline]
validate_chain+0x18e0/0x5900 kernel/locking/lockdep.c:3868
__lock_acquire+0x137a/0x2040 kernel/locking/lockdep.c:5142
lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5759
__mutex_lock_common kernel/locking/mutex.c:608 [inline]
__mutex_lock+0x136/0xd70 kernel/locking/mutex.c:752
autofs_write fs/autofs/waitq.c:55 [inline]
autofs_notify_daemon+0x71f/0xf80 fs/autofs/waitq.c:164
autofs_wait+0x10b8/0x1b30 fs/autofs/waitq.c:426
autofs_mount_wait+0x170/0x330 fs/autofs/root.c:255
autofs_d_automount+0x555/0x710 fs/autofs/root.c:401
follow_automount fs/namei.c:1394 [inline]
__traverse_mounts+0x2ba/0x580 fs/namei.c:1439
traverse_mounts fs/namei.c:1468 [inline]
handle_mounts fs/namei.c:1571 [inline]
step_into+0x5e5/0x1080 fs/namei.c:1877
lookup_last fs/namei.c:2542 [inline]
path_lookupat+0x16f/0x450 fs/namei.c:2566
filename_lookup+0x256/0x610 fs/namei.c:2595
kern_path+0x35/0x50 fs/namei.c:2703
lookup_bdev+0xc5/0x290 block/bdev.c:1157
resume_store+0x1a0/0x710 kernel/power/hibernate.c:1235
kernfs_fop_write_iter+0x3a1/0x500 fs/kernfs/file.c:334
iter_file_splice_write+0xbd7/0x14e0 fs/splice.c:743
do_splice_from fs/splice.c:941 [inline]
direct_splice_actor+0x11e/0x220 fs/splice.c:1164
splice_direct_to_actor+0x58e/0xc90 fs/splice.c:1108
do_splice_direct_actor fs/splice.c:1207 [inline]
do_splice_direct+0x28c/0x3e0 fs/splice.c:1233
do_sendfile+0x56d/0xe20 fs/read_write.c:1295
__do_sys_sendfile64 fs/read_write.c:1362 [inline]
__se_sys_sendfile64+0x17c/0x1e0 fs/read_write.c:1348
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
other info that might help us debug this:
Chain exists of:
&sbi->pipe_mutex --> &pipe->mutex --> &of->mutex
Possible unsafe locking scenario:
CPU0 CPU1
---- ----
lock(&of->mutex);
lock(&pipe->mutex);
lock(&of->mutex);
lock(&sbi->pipe_mutex);
*** DEADLOCK ***
3 locks held by syz.3.4748/19551:
#0: ffff88801e524420 (sb_writers#8){.+.+}-{0:0}, at: direct_splice_actor+0x49/0x220 fs/splice.c:1163
#1: ffff8880758e7888 (&of->mutex){+.+.}-{3:3}, at: kernfs_fop_write_iter+0x1eb/0x500 fs/kernfs/file.c:325
#2: ffff888017adb4b8 (kn->active#65){.+.+}-{0:0}, at: kernfs_fop_write_iter+0x20f/0x500 fs/kernfs/file.c:326
stack backtrace:
CPU: 1 PID: 19551 Comm: syz.3.4748 Not tainted 6.10.0-syzkaller-09703-gd7e78951a8b8 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/27/2024
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x241/0x360 lib/dump_stack.c:114
check_noncircular+0x36a/0x4a0 kernel/locking/lockdep.c:2186
check_prev_add kernel/locking/lockdep.c:3133 [inline]
check_prevs_add kernel/locking/lockdep.c:3252 [inline]
validate_chain+0x18e0/0x5900 kernel/locking/lockdep.c:3868
__lock_acquire+0x137a/0x2040 kernel/locking/lockdep.c:5142
lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5759
__mutex_lock_common kernel/locking/mutex.c:608 [inline]
__mutex_lock+0x136/0xd70 kernel/locking/mutex.c:752
autofs_write fs/autofs/waitq.c:55 [inline]
autofs_notify_daemon+0x71f/0xf80 fs/autofs/waitq.c:164
autofs_wait+0x10b8/0x1b30 fs/autofs/waitq.c:426
autofs_mount_wait+0x170/0x330 fs/autofs/root.c:255
autofs_d_automount+0x555/0x710 fs/autofs/root.c:401
follow_automount fs/namei.c:1394 [inline]
__traverse_mounts+0x2ba/0x580 fs/namei.c:1439
traverse_mounts fs/namei.c:1468 [inline]
handle_mounts fs/namei.c:1571 [inline]
step_into+0x5e5/0x1080 fs/namei.c:1877
lookup_last fs/namei.c:2542 [inline]
path_lookupat+0x16f/0x450 fs/namei.c:2566
filename_lookup+0x256/0x610 fs/namei.c:2595
kern_path+0x35/0x50 fs/namei.c:2703
lookup_bdev+0xc5/0x290 block/bdev.c:1157
resume_store+0x1a0/0x710 kernel/power/hibernate.c:1235
kernfs_fop_write_iter+0x3a1/0x500 fs/kernfs/file.c:334
iter_file_splice_write+0xbd7/0x14e0 fs/splice.c:743
do_splice_from fs/splice.c:941 [inline]
direct_splice_actor+0x11e/0x220 fs/splice.c:1164
splice_direct_to_actor+0x58e/0xc90 fs/splice.c:1108
do_splice_direct_actor fs/splice.c:1207 [inline]
do_splice_direct+0x28c/0x3e0 fs/splice.c:1233
do_sendfile+0x56d/0xe20 fs/read_write.c:1295
__do_sys_sendfile64 fs/read_write.c:1362 [inline]
__se_sys_sendfile64+0x17c/0x1e0 fs/read_write.c:1348
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f75ec575b59
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f75ebfde048 EFLAGS: 00000246 ORIG_RAX: 0000000000000028
RAX: ffffffffffffffda RBX: 00007f75ec706038 RCX: 00007f75ec575b59
RDX: 0000000000000000 RSI: 0000000000000004 RDI: 0000000000000004
RBP: 00007f75ec5e4e5d R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000246 R12: 0000000000000000
R13: 000000000000006e R14: 00007f75ec706038 R15: 00007ffef2866ed8
</TASK>
PM: Image not found (code -6)
---
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