Re: [syzbot] [nilfs?] KASAN: slab-out-of-bounds Read in wb_writeback

From: Christian Brauner
Date: Fri Apr 05 2024 - 07:06:47 EST

On Wed, Apr 03, 2024 at 11:47:17AM +0200, Jan Kara wrote:
> On Tue 02-04-24 07:38:25, syzbot wrote:
> > syzbot has found a reproducer for the following issue on:
> >
> > HEAD commit: c0b832517f62 Add linux-next specific files for 20240402
> > git tree: linux-next
> > console+strace: https://syzkaller.appspot.com/x/log.txt?x=14af7dd9180000
> > kernel config: https://syzkaller.appspot.com/x/.config?x=afcaf46d374cec8c
> > dashboard link: https://syzkaller.appspot.com/bug?extid=7b219b86935220db6dd8
> > compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1729f003180000
> > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17fa4341180000
> >
> > Downloadable assets:
> > disk image: https://storage.googleapis.com/syzbot-assets/0d36ec76edc7/disk-c0b83251.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/6f9bb4e37dd0/vmlinux-c0b83251.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/2349287b14b7/bzImage-c0b83251.xz
> > mounted in repro: https://storage.googleapis.com/syzbot-assets/9760c52a227c/mount_0.gz
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+7b219b86935220db6dd8@xxxxxxxxxxxxxxxxxxxxxxxxx
> >
> > ==================================================================
> > BUG: KASAN: slab-out-of-bounds in __lock_acquire+0x78/0x1fd0 kernel/locking/lockdep.c:5005
> > Read of size 8 at addr ffff888020485fa8 by task kworker/u8:2/35
>
> Looks like the writeback cleanups are causing some use-after-free issues.
> The code KASAN is complaining about is:
>
> /*
> * Nothing written. Wait for some inode to
> * become available for writeback. Otherwise
> * we'll just busyloop.
> */
> trace_writeback_wait(wb, work);
> inode = wb_inode(wb->b_more_io.prev);
> >>>>> spin_lock(&inode->i_lock); <<<<<<
> spin_unlock(&wb->list_lock);
> /* This function drops i_lock... */
> inode_sleep_on_writeback(inode);
>
> in wb_writeback(). Now looking at the changes indeed the commit
> 167d6693deb ("fs/writeback: bail out if there is no more inodes for IO and
> queued once") is buggy because it will result in trying to fetch 'inode'
> from empty b_more_io list and thus we'll corrupt memory. I think instead of
> modifying the condition:
>
> if (list_empty(&wb->b_more_io)) {
>
> we should do:
>
> - if (progress) {
> + if (progress || !queued) {
> spin_unlock(&wb->list_lock);
> continue;
> }
>
> Kemeng?

Fwiw, I observed this on xfstest too the last few days and tracked it
down to this series. Here's the splat I got in case it helps:

Apr 05 00:33:06 localhost kernel: ==================================================================
Apr 05 00:33:06 localhost kernel: BUG: KASAN: slab-out-of-bounds in __lock_acquire.isra.0+0x1075/0x1280
Apr 05 00:33:06 localhost kernel: Read of size 8 at addr ffff88810ed40f48 by task kworker/u128:2/305560
Apr 05 00:33:06 localhost kernel:
Apr 05 00:33:06 localhost kernel: CPU: 5 PID: 305560 Comm: kworker/u128:2 Not tainted 99.9.0-rc2-gdebeafad51e2 #262
Apr 05 00:33:06 localhost kernel: Hardware name: QEMU Standard PC (Q35 + ICH9, 2009)/Incus, BIOS unknown 2/2/2022
Apr 05 00:33:06 localhost kernel: Workqueue: writeback wb_workfn (flush-259:0)
Apr 05 00:33:06 localhost kernel: Call Trace:
Apr 05 00:33:06 localhost kernel: <TASK>
Apr 05 00:33:06 localhost kernel: dump_stack_lvl+0x5a/0x90
Apr 05 00:33:06 localhost kernel: print_report+0xce/0x650
Apr 05 00:33:06 localhost kernel: ? __virt_addr_valid+0x217/0x320
Apr 05 00:33:06 localhost kernel: kasan_report+0xd7/0x110
Apr 05 00:33:06 localhost kernel: ? __lock_acquire.isra.0+0x1075/0x1280
Apr 05 00:33:06 localhost kernel: ? __lock_acquire.isra.0+0x1075/0x1280
Apr 05 00:33:06 localhost kernel: __lock_acquire.isra.0+0x1075/0x1280
Apr 05 00:33:06 localhost kernel: lock_acquire+0x136/0x330
Apr 05 00:33:06 localhost kernel: ? wb_writeback+0x255/0x870
Apr 05 00:33:06 localhost kernel: _raw_spin_lock+0x33/0x40
Apr 05 00:33:06 localhost kernel: ? wb_writeback+0x255/0x870
Apr 05 00:33:06 localhost kernel: wb_writeback+0x255/0x870
Apr 05 00:33:06 localhost kernel: ? __pfx_wb_writeback+0x10/0x10
Apr 05 00:33:06 localhost kernel: ? __pfx_lock_release+0x10/0x10
Apr 05 00:33:06 localhost kernel: wb_workfn+0x221/0xc80
Apr 05 00:33:06 localhost kernel: ? __pfx_wb_workfn+0x10/0x10
Apr 05 00:33:06 localhost kernel: ? lock_acquire+0x136/0x330
Apr 05 00:33:06 localhost kernel: process_one_work+0x82d/0x1790
Apr 05 00:33:06 localhost kernel: ? __pfx_process_one_work+0x10/0x10
Apr 05 00:33:06 localhost kernel: ? assign_work+0x16c/0x240
Apr 05 00:33:06 localhost kernel: worker_thread+0x724/0x1300
Apr 05 00:33:06 localhost kernel: ? __kthread_parkme+0xba/0x1f0
Apr 05 00:33:06 localhost kernel: ? __pfx_worker_thread+0x10/0x10
Apr 05 00:33:06 localhost kernel: kthread+0x2ed/0x3d0
Apr 05 00:33:06 localhost kernel: ? __pfx_kthread+0x10/0x10
Apr 05 00:33:06 localhost kernel: ret_from_fork+0x31/0x70
Apr 05 00:33:06 localhost kernel: ? __pfx_kthread+0x10/0x10
Apr 05 00:33:06 localhost kernel: ret_from_fork_asm+0x1a/0x30
Apr 05 00:33:06 localhost kernel: </TASK>
Apr 05 00:33:06 localhost kernel:
Apr 05 00:33:06 localhost kernel: Allocated by task 1:
Apr 05 00:33:06 localhost kernel: kasan_save_stack+0x33/0x60
Apr 05 00:33:06 localhost kernel: kasan_save_track+0x14/0x30
Apr 05 00:33:06 localhost kernel: __kasan_kmalloc+0xaa/0xb0
Apr 05 00:33:06 localhost kernel: psi_cgroup_alloc+0x57/0x2b0
Apr 05 00:33:06 localhost kernel: cgroup_mkdir+0x4f8/0xfb0
Apr 05 00:33:06 localhost kernel: kernfs_iop_mkdir+0x133/0x1c0
Apr 05 00:33:06 localhost kernel: vfs_mkdir+0x3b9/0x610
Apr 05 00:33:06 localhost kernel: do_mkdirat+0x27e/0x300
Apr 05 00:33:06 localhost kernel: __x64_sys_mkdir+0x65/0x80
Apr 05 00:33:06 localhost kernel: do_syscall_64+0x64/0x190
Apr 05 00:33:06 localhost kernel: entry_SYSCALL_64_after_hwframe+0x71/0x79
Apr 05 00:33:06 localhost kernel:
Apr 05 00:33:06 localhost kernel: Last potentially related work creation:
Apr 05 00:33:06 localhost kernel: kasan_save_stack+0x33/0x60
Apr 05 00:33:06 localhost kernel: __kasan_record_aux_stack+0xad/0xc0
Apr 05 00:33:06 localhost kernel: insert_work+0x32/0x1f0
Apr 05 00:33:06 localhost kernel: __queue_work+0x5cb/0xcb0
Apr 05 00:33:06 localhost kernel: call_timer_fn+0x16d/0x490
Apr 05 00:33:06 localhost kernel: __run_timers+0x488/0x980
Apr 05 00:33:06 localhost kernel: run_timer_base+0xfb/0x170
Apr 05 00:33:06 localhost kernel: run_timer_softirq+0x1a/0x30
Apr 05 00:33:06 localhost kernel: __do_softirq+0x26a/0x7d2
Apr 05 00:33:06 localhost kernel:
Apr 05 00:33:06 localhost kernel: Second to last potentially related work creation:
Apr 05 00:33:06 localhost kernel: kasan_save_stack+0x33/0x60
Apr 05 00:33:06 localhost kernel: __kasan_record_aux_stack+0xad/0xc0
Apr 05 00:33:06 localhost kernel: insert_work+0x32/0x1f0
Apr 05 00:33:06 localhost kernel: __queue_work+0x5cb/0xcb0
Apr 05 00:33:06 localhost kernel: call_timer_fn+0x16d/0x490
Apr 05 00:33:06 localhost kernel: __run_timers+0x488/0x980
Apr 05 00:33:06 localhost kernel: timer_expire_remote+0xe6/0x150
Apr 05 00:33:06 localhost kernel: tmigr_handle_remote+0x6e2/0xe00
Apr 05 00:33:06 localhost kernel: __do_softirq+0x26a/0x7d2
Apr 05 00:33:06 localhost kernel:
Apr 05 00:33:06 localhost kernel: The buggy address belongs to the object at ffff88810ed40000
which belongs to the cache kmalloc-2k of size 2048
Apr 05 00:33:06 localhost kernel: The buggy address is located 2792 bytes to the right of
allocated 1120-byte region [ffff88810ed40000, ffff88810ed40460)
Apr 05 00:33:06 localhost kernel:
Apr 05 00:33:06 localhost kernel: The buggy address belongs to the physical page:
Apr 05 00:33:06 localhost kernel: page: refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff88810ed45000 pfn:0x10ed40
Apr 05 00:33:06 localhost kernel: head: order:3 entire_mapcount:0 nr_pages_mapped:0 pincount:0
Apr 05 00:33:06 localhost kernel: flags: 0x200000000000840(slab|head|node=0|zone=2)
Apr 05 00:33:06 localhost kernel: page_type: 0xffffffff()
Apr 05 00:33:06 localhost kernel: raw: 0200000000000840 ffff888100042f00 ffffea00040f1a00 dead000000000002
Apr 05 00:33:06 localhost kernel: raw: ffff88810ed45000 0000000080080006 00000001ffffffff 0000000000000000
Apr 05 00:33:06 localhost kernel: head: 0200000000000840 ffff888100042f00 ffffea00040f1a00 dead000000000002
Apr 05 00:33:06 localhost kernel: head: ffff88810ed45000 0000000080080006 00000001ffffffff 0000000000000000
Apr 05 00:33:06 localhost kernel: head: 0200000000000003 ffffea00043b5001 dead000000000122 00000000ffffffff
Apr 05 00:33:06 localhost kernel: head: 0000000800000000 0000000000000000 00000000ffffffff 0000000000000000
Apr 05 00:33:06 localhost kernel: page dumped because: kasan: bad access detected
Apr 05 00:33:06 localhost kernel:
Apr 05 00:33:06 localhost kernel: Memory state around the buggy address:
Apr 05 00:33:06 localhost kernel: ffff88810ed40e00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
Apr 05 00:33:06 localhost kernel: ffff88810ed40e80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
Apr 05 00:33:06 localhost kernel: >ffff88810ed40f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
Apr 05 00:33:06 localhost kernel: ^
Apr 05 00:33:06 localhost kernel: ffff88810ed40f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
Apr 05 00:33:06 localhost kernel: ffff88810ed41000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
Apr 05 00:33:06 localhost kernel: ==================================================================
Apr 05 00:33:06 localhost kernel: Disabling lock debugging due to kernel taint
Apr 05 00:33:06 localhost kernel: INFO: trying to register non-static key.
Apr 05 00:33:06 localhost kernel: The code is fine but needs lockdep annotation, or maybe
Apr 05 00:33:06 localhost kernel: you didn't initialize this object before use?
Apr 05 00:33:06 localhost kernel: turning off the locking correctness validator.
Apr 05 00:33:06 localhost kernel: CPU: 5 PID: 305560 Comm: kworker/u128:2 Tainted: G B 99.9.0-rc2-gdebeafad51e2 #262
Apr 05 00:33:06 localhost kernel: Hardware name: QEMU Standard PC (Q35 + ICH9, 2009)/Incus, BIOS unknown 2/2/2022
Apr 05 00:33:06 localhost kernel: Workqueue: writeback wb_workfn (flush-259:0)
Apr 05 00:33:06 localhost kernel: Call Trace:
Apr 05 00:33:06 localhost kernel: <TASK>
Apr 05 00:33:06 localhost kernel: dump_stack_lvl+0x5a/0x90
Apr 05 00:33:06 localhost kernel: register_lock_class+0x11dd/0x1860
Apr 05 00:33:06 localhost kernel: ? add_taint+0x2a/0x90
Apr 05 00:33:06 localhost kernel: ? end_report+0x85/0x180
Apr 05 00:33:06 localhost kernel: ? __pfx_register_lock_class+0x10/0x10
Apr 05 00:33:06 localhost kernel: __lock_acquire.isra.0+0x7f/0x1280
Apr 05 00:33:06 localhost kernel: lock_acquire+0x136/0x330
Apr 05 00:33:06 localhost kernel: ? wb_writeback+0x255/0x870
Apr 05 00:33:06 localhost kernel: _raw_spin_lock+0x33/0x40
Apr 05 00:33:06 localhost kernel: ? wb_writeback+0x255/0x870
Apr 05 00:33:06 localhost kernel: wb_writeback+0x255/0x870
Apr 05 00:33:06 localhost kernel: ? __pfx_wb_writeback+0x10/0x10
Apr 05 00:33:06 localhost kernel: ? __pfx_lock_release+0x10/0x10
Apr 05 00:33:06 localhost kernel: wb_workfn+0x221/0xc80
Apr 05 00:33:06 localhost kernel: ? __pfx_wb_workfn+0x10/0x10
Apr 05 00:33:06 localhost kernel: ? lock_acquire+0x136/0x330
Apr 05 00:33:06 localhost kernel: process_one_work+0x82d/0x1790
Apr 05 00:33:06 localhost kernel: ? __pfx_process_one_work+0x10/0x10
Apr 05 00:33:06 localhost kernel: ? assign_work+0x16c/0x240
Apr 05 00:33:06 localhost kernel: worker_thread+0x724/0x1300
Apr 05 00:33:06 localhost kernel: ? __kthread_parkme+0xba/0x1f0
Apr 05 00:33:06 localhost kernel: ? __pfx_worker_thread+0x10/0x10
Apr 05 00:33:06 localhost kernel: kthread+0x2ed/0x3d0
Apr 05 00:33:06 localhost kernel: ? __pfx_kthread+0x10/0x10
Apr 05 00:33:06 localhost kernel: ret_from_fork+0x31/0x70
Apr 05 00:33:06 localhost kernel: ? __pfx_kthread+0x10/0x10
Apr 05 00:33:06 localhost kernel: ret_from_fork_asm+0x1a/0x30
Apr 05 00:33:06 localhost kernel: </TASK>