* [PATCH] fs: Handle multiply claimed blocks more gracefully with mmb
@ 2026-04-22 14:45 Jan Kara
2026-04-23 7:14 ` [syzbot ci] " syzbot ci
0 siblings, 1 reply; 3+ messages in thread
From: Jan Kara @ 2026-04-22 14:45 UTC (permalink / raw)
To: Christian Brauner; +Cc: linux-fsdevel, Jan Kara, Ruikai Peng
When a metadata block is referenced by multiple inodes and tracked by
metadata bh infrastructure (which is forbidden and generally indicates
filesystem corruption), it can happen that mmb_mark_buffer_dirty() is
called for two different mmb structures in parallel. This can lead to a
corruption of mmb linked list. Handle that situation gracefully (at
least from mmb POV) by serializing on setting bh->b_mmb.
Reported-by: Ruikai Peng <ruikai@pwno.io>
Signed-off-by: Jan Kara <jack@suse.cz>
---
fs/buffer.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/fs/buffer.c b/fs/buffer.c
index d6e062c42a8d..35e7b63576cf 100644
--- a/fs/buffer.c
+++ b/fs/buffer.c
@@ -719,8 +719,15 @@ void mmb_mark_buffer_dirty(struct buffer_head *bh,
mark_buffer_dirty(bh);
if (!bh->b_mmb) {
spin_lock(&mmb->lock);
+ /*
+ * For a corrupted filesystem with multiply claimed blocks this
+ * can fail. Avoid corrupting the linked list in that case.
+ */
+ if (!cmpxchg(&bh->b_mmb, NULL, mmb)) {
+ spin_unlock(&mmb->lock);
+ return;
+ }
list_move_tail(&bh->b_assoc_buffers, &mmb->list);
- bh->b_mmb = mmb;
spin_unlock(&mmb->lock);
}
}
--
2.51.0
^ permalink raw reply related [flat|nested] 3+ messages in thread
* [syzbot ci] Re: fs: Handle multiply claimed blocks more gracefully with mmb
2026-04-22 14:45 [PATCH] fs: Handle multiply claimed blocks more gracefully with mmb Jan Kara
@ 2026-04-23 7:14 ` syzbot ci
2026-04-23 8:53 ` Jan Kara
0 siblings, 1 reply; 3+ messages in thread
From: syzbot ci @ 2026-04-23 7:14 UTC (permalink / raw)
To: brauner, jack, linux-fsdevel, ruikai; +Cc: syzbot, syzkaller-bugs
syzbot ci has tested the following series
[v1] fs: Handle multiply claimed blocks more gracefully with mmb
https://lore.kernel.org/all/20260422144529.20279-2-jack@suse.cz
* [PATCH] fs: Handle multiply claimed blocks more gracefully with mmb
and found the following issue:
KASAN: slab-use-after-free Read in remove_assoc_queue
Full report is available here:
https://ci.syzbot.org/series/3ac1baf5-8cbb-4927-a4b1-c051f76ce076
***
KASAN: slab-use-after-free Read in remove_assoc_queue
tree: torvalds
URL: https://kernel.googlesource.com/pub/scm/linux/kernel/git/torvalds/linux
base: 6596a02b207886e9e00bb0161c7fd59fea53c081
arch: amd64
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
config: https://ci.syzbot.org/builds/00926826-2798-4f8f-873a-dc81fc60996a/config
syz repro: https://ci.syzbot.org/findings/581a8917-90d5-4038-b419-a939f694a8c4/syz_repro
==================================================================
BUG: KASAN: slab-use-after-free in __raw_spin_lock include/linux/spinlock_api_smp.h:158 [inline]
BUG: KASAN: slab-use-after-free in _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:158
Read of size 1 at addr ffff88802341b418 by task syz-executor/5940
CPU: 1 UID: 0 PID: 5940 Comm: syz-executor Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Call Trace:
<TASK>
dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
print_address_description+0x55/0x1e0 mm/kasan/report.c:378
print_report+0x58/0x70 mm/kasan/report.c:482
kasan_report+0x117/0x150 mm/kasan/report.c:595
__kasan_check_byte+0x2a/0x40 mm/kasan/common.c:574
kasan_check_byte include/linux/kasan.h:402 [inline]
lock_acquire+0x84/0x350 kernel/locking/lockdep.c:5842
__raw_spin_lock include/linux/spinlock_api_smp.h:158 [inline]
_raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:158
spin_lock include/linux/spinlock.h:342 [inline]
remove_assoc_queue+0x14b/0x450 fs/buffer.c:514
drop_buffers+0x115/0x320 fs/buffer.c:2819
try_to_free_buffers+0x17d/0x300 fs/buffer.c:2873
block_invalidate_folio+0x5f8/0x730 fs/buffer.c:1571
folio_invalidate mm/truncate.c:140 [inline]
truncate_cleanup_folio+0xcb/0x190 mm/truncate.c:160
truncate_inode_pages_range+0x2ce/0xe30 mm/truncate.c:404
kill_bdev block/bdev.c:91 [inline]
blkdev_flush_mapping+0x109/0x2f0 block/bdev.c:720
blkdev_put_whole block/bdev.c:727 [inline]
bdev_release+0x417/0x650 block/bdev.c:1152
blkdev_release+0x15/0x20 block/fops.c:705
__fput+0x44f/0xa60 fs/file_table.c:510
fput_close_sync+0x11f/0x240 fs/file_table.c:615
__do_sys_close fs/open.c:1507 [inline]
__se_sys_close fs/open.c:1492 [inline]
__x64_sys_close+0x7e/0x110 fs/open.c:1492
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f44beb5d04e
Code: 08 0f 85 a5 a8 ff ff 49 89 fb 48 89 f0 48 89 d7 48 89 ce 4c 89 c2 4d 89 ca 4c 8b 44 24 08 4c 8b 4c 24 10 4c 89 5c 24 08 0f 05 <c3> 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 80 00 00 00 00 48 83 ec 08
RSP: 002b:00007ffd5f8fd628 EFLAGS: 00000246 ORIG_RAX: 0000000000000003
RAX: ffffffffffffffda RBX: 000055558c3e9500 RCX: 00007f44beb5d04e
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00007ffd5f8fd6cc R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000002
R13: 00000000000927c0 R14: 00000000000126bd R15: 00007ffd5f8fd720
</TASK>
Allocated by task 6273:
kasan_save_stack mm/kasan/common.c:57 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
unpoison_slab_object mm/kasan/common.c:340 [inline]
__kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:366
kasan_slab_alloc include/linux/kasan.h:253 [inline]
slab_post_alloc_hook mm/slub.c:4569 [inline]
slab_alloc_node mm/slub.c:4898 [inline]
kmem_cache_alloc_lru_noprof+0x2b8/0x640 mm/slub.c:4917
fat_alloc_inode+0x30/0xf0 fs/fat/inode.c:753
alloc_inode+0x6a/0x1b0 fs/inode.c:345
new_inode+0x22/0x170 fs/inode.c:1179
fat_fill_super+0x1c7c/0x3530 fs/fat/inode.c:1819
get_tree_bdev_flags+0x431/0x4f0 fs/super.c:1694
vfs_get_tree+0x92/0x2a0 fs/super.c:1754
fc_mount fs/namespace.c:1193 [inline]
do_new_mount_fc fs/namespace.c:3758 [inline]
do_new_mount+0x341/0xd30 fs/namespace.c:3834
do_mount fs/namespace.c:4167 [inline]
__do_sys_mount fs/namespace.c:4383 [inline]
__se_sys_mount+0x31d/0x420 fs/namespace.c:4360
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
Freed by task 5824:
kasan_save_stack mm/kasan/common.c:57 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
poison_slab_object mm/kasan/common.c:253 [inline]
__kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
kasan_slab_free include/linux/kasan.h:235 [inline]
slab_free_hook mm/slub.c:2689 [inline]
slab_free mm/slub.c:6246 [inline]
kmem_cache_free+0x182/0x650 mm/slub.c:6373
rcu_do_batch kernel/rcu/tree.c:2617 [inline]
rcu_core+0x7cd/0x1070 kernel/rcu/tree.c:2869
handle_softirqs+0x22a/0x840 kernel/softirq.c:622
do_softirq+0x76/0xd0 kernel/softirq.c:523
__local_bh_enable_ip+0xf8/0x130 kernel/softirq.c:450
local_bh_enable include/linux/bottom_half.h:33 [inline]
__alloc_skb+0x1aa/0x7d0 net/core/skbuff.c:697
alloc_skb include/linux/skbuff.h:1383 [inline]
__tcp_send_ack+0xae/0x4f0 net/ipv4/tcp_output.c:4470
tcp_cleanup_rbuf net/ipv4/tcp.c:1615 [inline]
tcp_recvmsg_locked+0x2dfa/0x3720 net/ipv4/tcp.c:2919
tcp_recvmsg+0x205/0x7e0 net/ipv4/tcp.c:2948
sock_recvmsg_nosec net/socket.c:1137 [inline]
sock_recvmsg+0xfa/0x1b0 net/socket.c:1159
sock_read_iter+0x251/0x320 net/socket.c:1229
new_sync_read fs/read_write.c:493 [inline]
vfs_read+0x582/0xa70 fs/read_write.c:574
ksys_read+0x150/0x270 fs/read_write.c:717
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x15f/0xf80 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:57
kasan_record_aux_stack+0xbd/0xd0 mm/kasan/generic.c:556
__call_rcu_common kernel/rcu/tree.c:3131 [inline]
call_rcu+0xee/0x890 kernel/rcu/tree.c:3251
destroy_inode fs/inode.c:399 [inline]
evict+0x95b/0xb10 fs/inode.c:865
dispose_list fs/inode.c:883 [inline]
evict_inodes+0x75a/0x7f0 fs/inode.c:937
generic_shutdown_super+0xaa/0x2d0 fs/super.c:632
kill_block_super+0x44/0x90 fs/super.c:1725
deactivate_locked_super+0xbc/0x130 fs/super.c:476
cleanup_mnt+0x437/0x4d0 fs/namespace.c:1312
task_work_run+0x1d9/0x270 kernel/task_work.c:233
resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
__exit_to_user_mode_loop kernel/entry/common.c:67 [inline]
exit_to_user_mode_loop+0xed/0x480 kernel/entry/common.c:98
__exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:238 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:318 [inline]
do_syscall_64+0x33e/0xf80 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f
The buggy address belongs to the object at ffff88802341b2c0
which belongs to the cache fat_inode_cache of size 1496
The buggy address is located 344 bytes inside of
freed 1496-byte region [ffff88802341b2c0, ffff88802341b898)
The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff888023419960 pfn:0x23418
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
memcg:ffff88802341fee1
flags: 0xfff00000000240(workingset|head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000240 ffff8881036e9780 ffffea000483a410 ffff8881052864c8
raw: ffff888023419960 0000000800140012 00000000f5000000 ffff88802341fee1
head: 00fff00000000240 ffff8881036e9780 ffffea000483a410 ffff8881052864c8
head: ffff888023419960 0000000800140012 00000000f5000000 ffff88802341fee1
head: 00fff00000000003 fffffffffffffe01 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 Reclaimable, gfp_mask 0xd2050(__GFP_RECLAIMABLE|__GFP_IO|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 6047, tgid 6046 (syz.1.52), ts 71569692880, free_ts 67561500883
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x231/0x280 mm/page_alloc.c:1858
prep_new_page mm/page_alloc.c:1866 [inline]
get_page_from_freelist+0x24ba/0x2540 mm/page_alloc.c:3946
__alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5226
alloc_slab_page mm/slub.c:3278 [inline]
allocate_slab+0x77/0x660 mm/slub.c:3467
new_slab mm/slub.c:3525 [inline]
refill_objects+0x339/0x3d0 mm/slub.c:7251
refill_sheaf mm/slub.c:2816 [inline]
__pcs_replace_empty_main+0x321/0x720 mm/slub.c:4651
alloc_from_pcs mm/slub.c:4749 [inline]
slab_alloc_node mm/slub.c:4883 [inline]
kmem_cache_alloc_lru_noprof+0x37c/0x640 mm/slub.c:4917
fat_alloc_inode+0x30/0xf0 fs/fat/inode.c:753
alloc_inode+0x6a/0x1b0 fs/inode.c:345
new_inode+0x22/0x170 fs/inode.c:1179
fat_fill_super+0x1bbc/0x3530 fs/fat/inode.c:1807
get_tree_bdev_flags+0x431/0x4f0 fs/super.c:1694
vfs_get_tree+0x92/0x2a0 fs/super.c:1754
fc_mount fs/namespace.c:1193 [inline]
do_new_mount_fc fs/namespace.c:3758 [inline]
do_new_mount+0x341/0xd30 fs/namespace.c:3834
do_mount fs/namespace.c:4167 [inline]
__do_sys_mount fs/namespace.c:4383 [inline]
__se_sys_mount+0x31d/0x420 fs/namespace.c:4360
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
page last free pid 5878 tgid 5878 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
__free_pages_prepare mm/page_alloc.c:1402 [inline]
__free_frozen_pages+0xbc7/0xd30 mm/page_alloc.c:2943
vfree+0x1d1/0x2f0 mm/vmalloc.c:3472
kcov_put kernel/kcov.c:442 [inline]
kcov_close+0x28/0x50 kernel/kcov.c:543
__fput+0x44f/0xa60 fs/file_table.c:510
task_work_run+0x1d9/0x270 kernel/task_work.c:233
exit_task_work include/linux/task_work.h:40 [inline]
do_exit+0x70f/0x22c0 kernel/exit.c:975
do_group_exit+0x21b/0x2d0 kernel/exit.c:1117
get_signal+0x1284/0x1330 kernel/signal.c:3037
arch_do_signal_or_restart+0xbc/0x830 arch/x86/kernel/signal.c:337
__exit_to_user_mode_loop kernel/entry/common.c:64 [inline]
exit_to_user_mode_loop+0x86/0x480 kernel/entry/common.c:98
__exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:238 [inline]
syscall_exit_to_user_mode include/linux/entry-common.h:318 [inline]
do_syscall_64+0x33e/0xf80 arch/x86/entry/syscall_64.c:100
entry_SYSCALL_64_after_hwframe+0x77/0x7f
Memory state around the buggy address:
ffff88802341b300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88802341b380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88802341b400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88802341b480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88802341b500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================
***
If these findings have caused you to resend the series or submit a
separate fix, please add the following tag to your commit message:
Tested-by: syzbot@syzkaller.appspotmail.com
---
This report is generated by a bot. It may contain errors.
syzbot ci engineers can be reached at syzkaller@googlegroups.com.
To test a patch for this bug, please reply with `#syz test`
(should be on a separate line).
The patch should be attached to the email.
Note: arguments like custom git repos and branches are not supported.
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [syzbot ci] Re: fs: Handle multiply claimed blocks more gracefully with mmb
2026-04-23 7:14 ` [syzbot ci] " syzbot ci
@ 2026-04-23 8:53 ` Jan Kara
0 siblings, 0 replies; 3+ messages in thread
From: Jan Kara @ 2026-04-23 8:53 UTC (permalink / raw)
To: syzbot ci; +Cc: brauner, jack, linux-fsdevel, ruikai, syzbot, syzkaller-bugs
On Thu 23-04-26 00:14:45, syzbot ci wrote:
> syzbot ci has tested the following series
>
> [v1] fs: Handle multiply claimed blocks more gracefully with mmb
> https://lore.kernel.org/all/20260422144529.20279-2-jack@suse.cz
> * [PATCH] fs: Handle multiply claimed blocks more gracefully with mmb
>
> and found the following issue:
> KASAN: slab-use-after-free Read in remove_assoc_queue
>
> Full report is available here:
> https://ci.syzbot.org/series/3ac1baf5-8cbb-4927-a4b1-c051f76ce076
Bah, indeed the patch is broken. I'll send v2.
Honza
>
> ***
>
> KASAN: slab-use-after-free Read in remove_assoc_queue
>
> tree: torvalds
> URL: https://kernel.googlesource.com/pub/scm/linux/kernel/git/torvalds/linux
> base: 6596a02b207886e9e00bb0161c7fd59fea53c081
> arch: amd64
> compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
> config: https://ci.syzbot.org/builds/00926826-2798-4f8f-873a-dc81fc60996a/config
> syz repro: https://ci.syzbot.org/findings/581a8917-90d5-4038-b419-a939f694a8c4/syz_repro
>
> ==================================================================
> BUG: KASAN: slab-use-after-free in __raw_spin_lock include/linux/spinlock_api_smp.h:158 [inline]
> BUG: KASAN: slab-use-after-free in _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:158
> Read of size 1 at addr ffff88802341b418 by task syz-executor/5940
>
> CPU: 1 UID: 0 PID: 5940 Comm: syz-executor Not tainted syzkaller #0 PREEMPT(full)
> Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
> Call Trace:
> <TASK>
> dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
> print_address_description+0x55/0x1e0 mm/kasan/report.c:378
> print_report+0x58/0x70 mm/kasan/report.c:482
> kasan_report+0x117/0x150 mm/kasan/report.c:595
> __kasan_check_byte+0x2a/0x40 mm/kasan/common.c:574
> kasan_check_byte include/linux/kasan.h:402 [inline]
> lock_acquire+0x84/0x350 kernel/locking/lockdep.c:5842
> __raw_spin_lock include/linux/spinlock_api_smp.h:158 [inline]
> _raw_spin_lock+0x2e/0x40 kernel/locking/spinlock.c:158
> spin_lock include/linux/spinlock.h:342 [inline]
> remove_assoc_queue+0x14b/0x450 fs/buffer.c:514
> drop_buffers+0x115/0x320 fs/buffer.c:2819
> try_to_free_buffers+0x17d/0x300 fs/buffer.c:2873
> block_invalidate_folio+0x5f8/0x730 fs/buffer.c:1571
> folio_invalidate mm/truncate.c:140 [inline]
> truncate_cleanup_folio+0xcb/0x190 mm/truncate.c:160
> truncate_inode_pages_range+0x2ce/0xe30 mm/truncate.c:404
> kill_bdev block/bdev.c:91 [inline]
> blkdev_flush_mapping+0x109/0x2f0 block/bdev.c:720
> blkdev_put_whole block/bdev.c:727 [inline]
> bdev_release+0x417/0x650 block/bdev.c:1152
> blkdev_release+0x15/0x20 block/fops.c:705
> __fput+0x44f/0xa60 fs/file_table.c:510
> fput_close_sync+0x11f/0x240 fs/file_table.c:615
> __do_sys_close fs/open.c:1507 [inline]
> __se_sys_close fs/open.c:1492 [inline]
> __x64_sys_close+0x7e/0x110 fs/open.c:1492
> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f44beb5d04e
> Code: 08 0f 85 a5 a8 ff ff 49 89 fb 48 89 f0 48 89 d7 48 89 ce 4c 89 c2 4d 89 ca 4c 8b 44 24 08 4c 8b 4c 24 10 4c 89 5c 24 08 0f 05 <c3> 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 80 00 00 00 00 48 83 ec 08
> RSP: 002b:00007ffd5f8fd628 EFLAGS: 00000246 ORIG_RAX: 0000000000000003
> RAX: ffffffffffffffda RBX: 000055558c3e9500 RCX: 00007f44beb5d04e
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000003
> RBP: 00007ffd5f8fd6cc R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000002
> R13: 00000000000927c0 R14: 00000000000126bd R15: 00007ffd5f8fd720
> </TASK>
>
> Allocated by task 6273:
> kasan_save_stack mm/kasan/common.c:57 [inline]
> kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
> unpoison_slab_object mm/kasan/common.c:340 [inline]
> __kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:366
> kasan_slab_alloc include/linux/kasan.h:253 [inline]
> slab_post_alloc_hook mm/slub.c:4569 [inline]
> slab_alloc_node mm/slub.c:4898 [inline]
> kmem_cache_alloc_lru_noprof+0x2b8/0x640 mm/slub.c:4917
> fat_alloc_inode+0x30/0xf0 fs/fat/inode.c:753
> alloc_inode+0x6a/0x1b0 fs/inode.c:345
> new_inode+0x22/0x170 fs/inode.c:1179
> fat_fill_super+0x1c7c/0x3530 fs/fat/inode.c:1819
> get_tree_bdev_flags+0x431/0x4f0 fs/super.c:1694
> vfs_get_tree+0x92/0x2a0 fs/super.c:1754
> fc_mount fs/namespace.c:1193 [inline]
> do_new_mount_fc fs/namespace.c:3758 [inline]
> do_new_mount+0x341/0xd30 fs/namespace.c:3834
> do_mount fs/namespace.c:4167 [inline]
> __do_sys_mount fs/namespace.c:4383 [inline]
> __se_sys_mount+0x31d/0x420 fs/namespace.c:4360
> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> Freed by task 5824:
> kasan_save_stack mm/kasan/common.c:57 [inline]
> kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
> kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
> poison_slab_object mm/kasan/common.c:253 [inline]
> __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
> kasan_slab_free include/linux/kasan.h:235 [inline]
> slab_free_hook mm/slub.c:2689 [inline]
> slab_free mm/slub.c:6246 [inline]
> kmem_cache_free+0x182/0x650 mm/slub.c:6373
> rcu_do_batch kernel/rcu/tree.c:2617 [inline]
> rcu_core+0x7cd/0x1070 kernel/rcu/tree.c:2869
> handle_softirqs+0x22a/0x840 kernel/softirq.c:622
> do_softirq+0x76/0xd0 kernel/softirq.c:523
> __local_bh_enable_ip+0xf8/0x130 kernel/softirq.c:450
> local_bh_enable include/linux/bottom_half.h:33 [inline]
> __alloc_skb+0x1aa/0x7d0 net/core/skbuff.c:697
> alloc_skb include/linux/skbuff.h:1383 [inline]
> __tcp_send_ack+0xae/0x4f0 net/ipv4/tcp_output.c:4470
> tcp_cleanup_rbuf net/ipv4/tcp.c:1615 [inline]
> tcp_recvmsg_locked+0x2dfa/0x3720 net/ipv4/tcp.c:2919
> tcp_recvmsg+0x205/0x7e0 net/ipv4/tcp.c:2948
> sock_recvmsg_nosec net/socket.c:1137 [inline]
> sock_recvmsg+0xfa/0x1b0 net/socket.c:1159
> sock_read_iter+0x251/0x320 net/socket.c:1229
> new_sync_read fs/read_write.c:493 [inline]
> vfs_read+0x582/0xa70 fs/read_write.c:574
> ksys_read+0x150/0x270 fs/read_write.c:717
> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> do_syscall_64+0x15f/0xf80 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:57
> kasan_record_aux_stack+0xbd/0xd0 mm/kasan/generic.c:556
> __call_rcu_common kernel/rcu/tree.c:3131 [inline]
> call_rcu+0xee/0x890 kernel/rcu/tree.c:3251
> destroy_inode fs/inode.c:399 [inline]
> evict+0x95b/0xb10 fs/inode.c:865
> dispose_list fs/inode.c:883 [inline]
> evict_inodes+0x75a/0x7f0 fs/inode.c:937
> generic_shutdown_super+0xaa/0x2d0 fs/super.c:632
> kill_block_super+0x44/0x90 fs/super.c:1725
> deactivate_locked_super+0xbc/0x130 fs/super.c:476
> cleanup_mnt+0x437/0x4d0 fs/namespace.c:1312
> task_work_run+0x1d9/0x270 kernel/task_work.c:233
> resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
> __exit_to_user_mode_loop kernel/entry/common.c:67 [inline]
> exit_to_user_mode_loop+0xed/0x480 kernel/entry/common.c:98
> __exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
> syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:238 [inline]
> syscall_exit_to_user_mode include/linux/entry-common.h:318 [inline]
> do_syscall_64+0x33e/0xf80 arch/x86/entry/syscall_64.c:100
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> The buggy address belongs to the object at ffff88802341b2c0
> which belongs to the cache fat_inode_cache of size 1496
> The buggy address is located 344 bytes inside of
> freed 1496-byte region [ffff88802341b2c0, ffff88802341b898)
>
> The buggy address belongs to the physical page:
> page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff888023419960 pfn:0x23418
> head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
> memcg:ffff88802341fee1
> flags: 0xfff00000000240(workingset|head|node=0|zone=1|lastcpupid=0x7ff)
> page_type: f5(slab)
> raw: 00fff00000000240 ffff8881036e9780 ffffea000483a410 ffff8881052864c8
> raw: ffff888023419960 0000000800140012 00000000f5000000 ffff88802341fee1
> head: 00fff00000000240 ffff8881036e9780 ffffea000483a410 ffff8881052864c8
> head: ffff888023419960 0000000800140012 00000000f5000000 ffff88802341fee1
> head: 00fff00000000003 fffffffffffffe01 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 Reclaimable, gfp_mask 0xd2050(__GFP_RECLAIMABLE|__GFP_IO|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 6047, tgid 6046 (syz.1.52), ts 71569692880, free_ts 67561500883
> set_page_owner include/linux/page_owner.h:32 [inline]
> post_alloc_hook+0x231/0x280 mm/page_alloc.c:1858
> prep_new_page mm/page_alloc.c:1866 [inline]
> get_page_from_freelist+0x24ba/0x2540 mm/page_alloc.c:3946
> __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5226
> alloc_slab_page mm/slub.c:3278 [inline]
> allocate_slab+0x77/0x660 mm/slub.c:3467
> new_slab mm/slub.c:3525 [inline]
> refill_objects+0x339/0x3d0 mm/slub.c:7251
> refill_sheaf mm/slub.c:2816 [inline]
> __pcs_replace_empty_main+0x321/0x720 mm/slub.c:4651
> alloc_from_pcs mm/slub.c:4749 [inline]
> slab_alloc_node mm/slub.c:4883 [inline]
> kmem_cache_alloc_lru_noprof+0x37c/0x640 mm/slub.c:4917
> fat_alloc_inode+0x30/0xf0 fs/fat/inode.c:753
> alloc_inode+0x6a/0x1b0 fs/inode.c:345
> new_inode+0x22/0x170 fs/inode.c:1179
> fat_fill_super+0x1bbc/0x3530 fs/fat/inode.c:1807
> get_tree_bdev_flags+0x431/0x4f0 fs/super.c:1694
> vfs_get_tree+0x92/0x2a0 fs/super.c:1754
> fc_mount fs/namespace.c:1193 [inline]
> do_new_mount_fc fs/namespace.c:3758 [inline]
> do_new_mount+0x341/0xd30 fs/namespace.c:3834
> do_mount fs/namespace.c:4167 [inline]
> __do_sys_mount fs/namespace.c:4383 [inline]
> __se_sys_mount+0x31d/0x420 fs/namespace.c:4360
> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> do_syscall_64+0x15f/0xf80 arch/x86/entry/syscall_64.c:94
> page last free pid 5878 tgid 5878 stack trace:
> reset_page_owner include/linux/page_owner.h:25 [inline]
> __free_pages_prepare mm/page_alloc.c:1402 [inline]
> __free_frozen_pages+0xbc7/0xd30 mm/page_alloc.c:2943
> vfree+0x1d1/0x2f0 mm/vmalloc.c:3472
> kcov_put kernel/kcov.c:442 [inline]
> kcov_close+0x28/0x50 kernel/kcov.c:543
> __fput+0x44f/0xa60 fs/file_table.c:510
> task_work_run+0x1d9/0x270 kernel/task_work.c:233
> exit_task_work include/linux/task_work.h:40 [inline]
> do_exit+0x70f/0x22c0 kernel/exit.c:975
> do_group_exit+0x21b/0x2d0 kernel/exit.c:1117
> get_signal+0x1284/0x1330 kernel/signal.c:3037
> arch_do_signal_or_restart+0xbc/0x830 arch/x86/kernel/signal.c:337
> __exit_to_user_mode_loop kernel/entry/common.c:64 [inline]
> exit_to_user_mode_loop+0x86/0x480 kernel/entry/common.c:98
> __exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
> syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:238 [inline]
> syscall_exit_to_user_mode include/linux/entry-common.h:318 [inline]
> do_syscall_64+0x33e/0xf80 arch/x86/entry/syscall_64.c:100
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> Memory state around the buggy address:
> ffff88802341b300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff88802341b380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> >ffff88802341b400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ^
> ffff88802341b480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff88802341b500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
>
>
> ***
>
> If these findings have caused you to resend the series or submit a
> separate fix, please add the following tag to your commit message:
> Tested-by: syzbot@syzkaller.appspotmail.com
>
> ---
> This report is generated by a bot. It may contain errors.
> syzbot ci engineers can be reached at syzkaller@googlegroups.com.
>
> To test a patch for this bug, please reply with `#syz test`
> (should be on a separate line).
>
> The patch should be attached to the email.
> Note: arguments like custom git repos and branches are not supported.
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
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2026-04-22 14:45 [PATCH] fs: Handle multiply claimed blocks more gracefully with mmb Jan Kara
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