Message-ID: <687a7fe2.a00a0220.3af5df.002d.GAE@google.com>
Date: Fri, 18 Jul 2025 10:09:54 -0700
From: syzbot <syzbot+2b98caf09c41174a9697@...kaller.appspotmail.com>
To: kent.overstreet@...ux.dev
Cc: kent.overstreet@...ux.dev, linux-bcachefs@...r.kernel.org, 
	linux-kernel@...r.kernel.org, syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [bcachefs?] KASAN: slab-use-after-free Write in bch2_get_next_dev

> On Fri, Jul 18, 2025 at 09:09:35AM -0700, syzbot wrote:
>> Hello,
>> 
>> syzbot found the following issue on:
>> 
>> HEAD commit:    024e09e444bd Add linux-next specific files for 20250717
>> git tree:       linux-next
>> console output: https://syzkaller.appspot.com/x/log.txt?x=107317d4580000
>> kernel config:  https://syzkaller.appspot.com/x/.config?x=99c60e2181be9059
>> dashboard link: https://syzkaller.appspot.com/bug?extid=2b98caf09c41174a9697
>> compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
>> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=11ad7d8c580000
>> 
>> Downloadable assets:
>> disk image: https://storage.googleapis.com/syzbot-assets/0a89a1e83302/disk-024e09e4.raw.xz
>> vmlinux: https://storage.googleapis.com/syzbot-assets/e2264946780a/vmlinux-024e09e4.xz
>> kernel image: https://storage.googleapis.com/syzbot-assets/d684a7204e1c/bzImage-024e09e4.xz
>> mounted in repro: https://storage.googleapis.com/syzbot-assets/5f7f631c7091/mount_2.gz
>> 
>> IMPORTANT: if you fix the issue, please add the following tag to the commit:
>> Reported-by: syzbot+2b98caf09c41174a9697@...kaller.appspotmail.com
>> 
>> ==================================================================
>> BUG: KASAN: slab-use-after-free in instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
>> BUG: KASAN: slab-use-after-free in atomic_long_inc_return include/linux/atomic/atomic-instrumented.h:3609 [inline]
>> BUG: KASAN: slab-use-after-free in bch2_dev_get fs/bcachefs/sb-members.h:114 [inline]
>> BUG: KASAN: slab-use-after-free in bch2_get_next_dev+0x38f/0x4e0 fs/bcachefs/sb-members.h:145
>> Write of size 8 at addr ffff888029ae2040 by task kworker/u9:0/51
>> 
>> CPU: 1 UID: 0 PID: 51 Comm: kworker/u9:0 Not tainted 6.16.0-rc6-next-20250717-syzkaller #0 PREEMPT(full) 
>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
>> Workqueue: bcachefs_journal journal_write_done
>> Call Trace:
>>  <TASK>
>>  dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
>>  print_address_description mm/kasan/report.c:378 [inline]
>>  print_report+0xca/0x230 mm/kasan/report.c:480
>>  kasan_report+0x118/0x150 mm/kasan/report.c:593
>>  check_region_inline mm/kasan/generic.c:-1 [inline]
>>  kasan_check_range+0x2b0/0x2c0 mm/kasan/generic.c:189
>>  instrument_atomic_read_write include/linux/instrumented.h:96 [inline]
>>  atomic_long_inc_return include/linux/atomic/atomic-instrumented.h:3609 [inline]
>>  bch2_dev_get fs/bcachefs/sb-members.h:114 [inline]
>>  bch2_get_next_dev+0x38f/0x4e0 fs/bcachefs/sb-members.h:145
>>  bch2_do_discards+0x20/0x160 fs/bcachefs/alloc_background.c:1935
>>  journal_write_done+0x11b9/0x13f0 fs/bcachefs/journal_io.c:1822
>>  process_one_work kernel/workqueue.c:3239 [inline]
>>  process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3322
>>  worker_thread+0x8a0/0xda0 kernel/workqueue.c:3403
>>  kthread+0x70e/0x8a0 kernel/kthread.c:463
>>  ret_from_fork+0x3f9/0x770 arch/x86/kernel/process.c:148
>>  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
>>  </TASK>
>> 
>> Allocated by task 7622:
>>  kasan_save_stack mm/kasan/common.c:47 [inline]
>>  kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
>>  poison_kmalloc_redzone mm/kasan/common.c:377 [inline]
>>  __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:394
>>  kasan_kmalloc include/linux/kasan.h:260 [inline]
>>  __kmalloc_cache_noprof+0x230/0x3d0 mm/slub.c:4396
>>  kmalloc_noprof include/linux/slab.h:905 [inline]
>>  kzalloc_noprof include/linux/slab.h:1039 [inline]
>>  __bch2_dev_alloc+0xa7/0xc30 fs/bcachefs/super.c:1487
>>  bch2_dev_alloc+0xcd/0x180 fs/bcachefs/super.c:1558
>>  bch2_fs_alloc fs/bcachefs/super.c:1068 [inline]
>>  bch2_fs_open+0x256f/0x2760 fs/bcachefs/super.c:2395
>>  bch2_fs_get_tree+0x44f/0x1540 fs/bcachefs/fs.c:2440
>>  vfs_get_tree+0x8f/0x2b0 fs/super.c:1815
>>  do_new_mount+0x2a2/0x9e0 fs/namespace.c:3805
>>  do_mount fs/namespace.c:4133 [inline]
>>  __do_sys_mount fs/namespace.c:4344 [inline]
>>  __se_sys_mount+0x317/0x410 fs/namespace.c:4321
>>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>>  do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
>>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
>> 
>> Freed by task 7622:
>>  kasan_save_stack mm/kasan/common.c:47 [inline]
>>  kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
>>  kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:576
>>  poison_slab_object mm/kasan/common.c:247 [inline]
>>  __kasan_slab_free+0x62/0x70 mm/kasan/common.c:264
>>  kasan_slab_free include/linux/kasan.h:233 [inline]
>>  slab_free_hook mm/slub.c:2417 [inline]
>>  slab_free mm/slub.c:4680 [inline]
>>  kfree+0x18e/0x440 mm/slub.c:4879
>>  kobject_cleanup lib/kobject.c:689 [inline]
>>  kobject_release lib/kobject.c:720 [inline]
>>  kref_put include/linux/kref.h:65 [inline]
>>  kobject_put+0x22b/0x480 lib/kobject.c:737
>>  bch2_fs_free+0x4b3/0x5c0 fs/bcachefs/super.c:749
>>  bch2_fs_get_tree+0xb76/0x1540 fs/bcachefs/fs.c:2572
>>  vfs_get_tree+0x8f/0x2b0 fs/super.c:1815
>>  do_new_mount+0x2a2/0x9e0 fs/namespace.c:3805
>>  do_mount fs/namespace.c:4133 [inline]
>>  __do_sys_mount fs/namespace.c:4344 [inline]
>>  __se_sys_mount+0x317/0x410 fs/namespace.c:4321
>>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>>  do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
>>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
>> 
>> Last potentially related work creation:
>>  kasan_save_stack+0x3e/0x60 mm/kasan/common.c:47
>>  kasan_record_aux_stack+0xbd/0xd0 mm/kasan/generic.c:548
>>  insert_work+0x3d/0x330 kernel/workqueue.c:2187
>>  __queue_work+0xcd2/0xfb0 kernel/workqueue.c:2342
>>  queue_work_on+0x181/0x270 kernel/workqueue.c:2393
>>  bch2_btree_node_read_done+0x159b/0x5560 fs/bcachefs/btree_io.c:1156
>>  btree_node_read_work+0x4ee/0xfa0 fs/bcachefs/btree_io.c:1444
>>  bch2_btree_node_read+0x83e/0x2aa0 fs/bcachefs/btree_io.c:1865
>>  __bch2_btree_root_read fs/bcachefs/btree_io.c:1906 [inline]
>>  bch2_btree_root_read+0x5e5/0x780 fs/bcachefs/btree_io.c:1928
>>  read_btree_roots+0x2b7/0x850 fs/bcachefs/recovery.c:602
>>  bch2_fs_recovery+0x2513/0x38a0 fs/bcachefs/recovery.c:985
>>  bch2_fs_start+0xa0f/0xcc0 fs/bcachefs/super.c:1216
>>  bch2_fs_get_tree+0xb39/0x1540 fs/bcachefs/fs.c:2456
>>  vfs_get_tree+0x8f/0x2b0 fs/super.c:1815
>>  do_new_mount+0x2a2/0x9e0 fs/namespace.c:3805
>>  do_mount fs/namespace.c:4133 [inline]
>>  __do_sys_mount fs/namespace.c:4344 [inline]
>>  __se_sys_mount+0x317/0x410 fs/namespace.c:4321
>>  do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
>>  do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
>>  entry_SYSCALL_64_after_hwframe+0x77/0x7f
>> 
>> The buggy address belongs to the object at ffff888029ae2000
>>  which belongs to the cache kmalloc-4k of size 4096
>> The buggy address is located 64 bytes inside of
>>  freed 4096-byte region [ffff888029ae2000, ffff888029ae3000)
>> 
>> The buggy address belongs to the physical page:
>> page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x29ae0
>> head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
>> flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
>> page_type: f5(slab)
>> raw: 00fff00000000040 ffff88801a442140 dead000000000122 0000000000000000
>> raw: 0000000000000000 0000000000040004 00000000f5000000 0000000000000000
>> head: 00fff00000000040 ffff88801a442140 dead000000000122 0000000000000000
>> head: 0000000000000000 0000000000040004 00000000f5000000 0000000000000000
>> head: 00fff00000000003 ffffea0000a6b801 00000000ffffffff 00000000ffffffff
>> head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000008
>> page dumped because: kasan: bad access detected
>> page_owner tracks the page as allocated
>> page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd2820(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 59, tgid 59 (kworker/u8:4), ts 293379161383, free_ts 284295390486
>>  set_page_owner include/linux/page_owner.h:32 [inline]
>>  post_alloc_hook+0x240/0x2a0 mm/page_alloc.c:1851
>>  prep_new_page mm/page_alloc.c:1859 [inline]
>>  get_page_from_freelist+0x21e4/0x22c0 mm/page_alloc.c:3858
>>  __alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5148
>>  alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2416
>>  alloc_slab_page mm/slub.c:2487 [inline]
>>  allocate_slab+0x8a/0x370 mm/slub.c:2655
>>  new_slab mm/slub.c:2709 [inline]
>>  ___slab_alloc+0xbeb/0x1410 mm/slub.c:3891
>>  __slab_alloc mm/slub.c:3981 [inline]
>>  __slab_alloc_node mm/slub.c:4056 [inline]
>>  slab_alloc_node mm/slub.c:4217 [inline]
>>  __do_kmalloc_node mm/slub.c:4364 [inline]
>>  __kmalloc_node_track_caller_noprof+0x2f8/0x4e0 mm/slub.c:4384
>>  kmalloc_reserve+0x136/0x290 net/core/skbuff.c:600
>>  __alloc_skb+0x142/0x2d0 net/core/skbuff.c:669
>>  alloc_skb include/linux/skbuff.h:1336 [inline]
>>  nsim_dev_trap_skb_build drivers/net/netdevsim/dev.c:761 [inline]
>>  nsim_dev_trap_report drivers/net/netdevsim/dev.c:818 [inline]
>>  nsim_dev_trap_report_work+0x29a/0xb80 drivers/net/netdevsim/dev.c:864
>>  process_one_work kernel/workqueue.c:3239 [inline]
>>  process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3322
>>  worker_thread+0x8a0/0xda0 kernel/workqueue.c:3403
>>  kthread+0x70e/0x8a0 kernel/kthread.c:463
>>  ret_from_fork+0x3f9/0x770 arch/x86/kernel/process.c:148
>>  ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
>> page last free pid 7530 tgid 7530 stack trace:
>>  reset_page_owner include/linux/page_owner.h:25 [inline]
>>  free_pages_prepare mm/page_alloc.c:1395 [inline]
>>  __free_frozen_pages+0xbc4/0xd30 mm/page_alloc.c:2895
>>  discard_slab mm/slub.c:2753 [inline]
>>  __put_partials+0x156/0x1a0 mm/slub.c:3218
>>  put_cpu_partial+0x17c/0x250 mm/slub.c:3293
>>  __slab_free+0x2d5/0x3c0 mm/slub.c:4550
>>  qlink_free mm/kasan/quarantine.c:163 [inline]
>>  qlist_free_all+0x97/0x140 mm/kasan/quarantine.c:179
>>  kasan_quarantine_reduce+0x148/0x160 mm/kasan/quarantine.c:286
>>  __kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:329
>>  kasan_slab_alloc include/linux/kasan.h:250 [inline]
>>  slab_post_alloc_hook mm/slub.c:4180 [inline]
>>  slab_alloc_node mm/slub.c:4229 [inline]
>>  __do_kmalloc_node mm/slub.c:4364 [inline]
>>  __kmalloc_node_track_caller_noprof+0x216/0x4e0 mm/slub.c:4384
>>  __do_krealloc mm/slub.c:4942 [inline]
>>  krealloc_noprof+0x124/0x340 mm/slub.c:4995
>>  bch2_printbuf_make_room+0x1f5/0x360 fs/bcachefs/printbuf.c:59
>>  bch2_prt_printf+0x282/0x740 fs/bcachefs/printbuf.c:186
>>  bch2_btree_path_to_text_short+0x148/0xde0 fs/bcachefs/btree_iter.c:1516
>>  __bch2_trans_paths_to_text+0xe5/0x190 fs/bcachefs/btree_iter.c:1589
>>  bch2_trans_update_max_paths+0x15f/0x390 fs/bcachefs/btree_iter.c:1625
>>  btree_path_alloc+0x89a/0xa70 fs/bcachefs/btree_iter.c:1718
>>  bch2_path_get+0x8bd/0x1540 fs/bcachefs/btree_iter.c:1774
>> 
>> Memory state around the buggy address:
>>  ffff888029ae1f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>>  ffff888029ae1f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>> >ffff888029ae2000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>                                            ^
>>  ffff888029ae2080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>>  ffff888029ae2100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>> ==================================================================
>> 
>> 
>> ---
>> This report is generated by a bot. It may contain errors.
>> See https://goo.gl/tpsmEJ for more information about syzbot.
>> syzbot engineers can be reached at syzkaller@...glegroups.com.
>> 
>> syzbot will keep track of this issue. See:
>> https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
>> 
>> If the report is already addressed, let syzbot know by replying with:
>> #syz fix: exact-commit-title
>> 
>> If you want syzbot to run the reproducer, reply with:
>> #syz test: git://repo/address.git branch-or-commit-hash
>> If you attach or paste a git patch, syzbot will apply it before testing.
>
> #syz test:

want either no args or 2 args (repo, branch), got 7

>
> From 84e7f95c41c2317265b3fb5a0524ed51c1d85aa4 Mon Sep 17 00:00:00 2001
> From: Kent Overstreet <kent.overstreet@...ux.dev>
> Date: Fri, 18 Jul 2025 13:04:43 -0400
> Subject: [PATCH] bcachefs: Fix UAF by journal write path
>
> Previously, we handled synchronization with shutdown vs. the journal
> write path by holding the journal lock until we were done, after marking
> the write as completed.
>
> But we don't want to be kicking off discards under the journal lock, so
> we need an actual ref - just set the journal write closure's parent to
> bch_fs.cl.
>
> Fixes: b4d6e204f892 ("bcachefs: Fix triggering of discard by the journal path")
> Signed-off-by: Kent Overstreet <kent.overstreet@...ux.dev>
>
> diff --git a/fs/bcachefs/journal.c b/fs/bcachefs/journal.c
> index de03e20f6e30..376c9b3b20fe 100644
> --- a/fs/bcachefs/journal.c
> +++ b/fs/bcachefs/journal.c
> @@ -182,6 +182,8 @@ journal_error_check_stuck(struct journal *j, int error, unsigned flags)
>  
>  void bch2_journal_do_writes(struct journal *j)
>  {
> +	struct bch_fs *c = container_of(j, struct bch_fs, journal);
> +
>  	for (u64 seq = journal_last_unwritten_seq(j);
>  	     seq <= journal_cur_seq(j);
>  	     seq++) {
> @@ -196,7 +198,7 @@ void bch2_journal_do_writes(struct journal *j)
>  		if (!journal_state_seq_count(j, j->reservations, seq)) {
>  			j->seq_write_started = seq;
>  			w->write_started = true;
> -			closure_call(&w->io, bch2_journal_write, j->wq, NULL);
> +			closure_call(&w->io, bch2_journal_write, j->wq, &c->cl);
>  		}
>  
>  		break;

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