syzbot


KASAN: slab-use-after-free Write in btrfs_put_root

Status: upstream: reported on 2026/06/02 11:26
Subsystems: btrfs
Labels: prio:high actionable
[Documentation on labels]
Reported-by: syzbot+b3d472d13f9d7bf20669@syzkaller.appspotmail.com
First crash: 11d, last: 3h40m
✨ AI Jobs (2)
ID Workflow Result Correct Bug Created Started Finished Revision Error
b0c8c364-3574-4284-9cfe-5a9d65f07ed7 moderation Actionable: ✅ KASAN: slab-use-after-free Write in btrfs_put_root 2026/06/02 10:23 2026/06/02 10:23 2026/06/02 11:25 1095583bae1d2729a3b4be301cb6ddc85ced9e38
ef4c4a12-097a-4049-9fa8-e1ef776e8856 assessment-security DenialOfService: ✅ Exploitable: ✅ FilesystemTrigger: ✅ NetworkTrigger: ❌ PeripheralTrigger: ✅ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ❌ KASAN: slab-use-after-free Write in btrfs_put_root 2026/06/02 10:05 2026/06/02 10:05 2026/06/02 11:03 1095583bae1d2729a3b4be301cb6ddc85ced9e38
Discussions (2)
Title Replies (including bot) Last reply
[syzbot] Monthly btrfs report (Jun 2026) 0 (1) 2026/06/03 04:32
[syzbot] [btrfs?] KASAN: slab-use-after-free Write in btrfs_put_root 0 (1) 2026/06/02 11:26

Sample crash report:
BTRFS info (device loop0 state EA): scrub: started on devid 1
BTRFS info (device loop0 state EA): scrub: not finished on devid 1 with status: -30
BTRFS info (device loop0 state EA): last unmount of filesystem 3a375e4e-b156-4d76-a2ad-16e198ce1409
==================================================================
BUG: KASAN: slab-use-after-free in instrument_atomic_read_write include/linux/instrumented.h:112 [inline]
BUG: KASAN: slab-use-after-free in atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline]
BUG: KASAN: slab-use-after-free in __refcount_sub_and_test include/linux/refcount.h:389 [inline]
BUG: KASAN: slab-use-after-free in __refcount_dec_and_test include/linux/refcount.h:432 [inline]
BUG: KASAN: slab-use-after-free in refcount_dec_and_test include/linux/refcount.h:450 [inline]
BUG: KASAN: slab-use-after-free in btrfs_put_root+0x2f/0x250 fs/btrfs/disk-io.c:1806
Write of size 4 at addr ffff888012bf8630 by task syz.0.0/5335

CPU: 0 UID: 0 PID: 5335 Comm: syz.0.0 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 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
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x264/0x2c0 mm/kasan/generic.c:200
 instrument_atomic_read_write include/linux/instrumented.h:112 [inline]
 atomic_fetch_sub_release include/linux/atomic/atomic-instrumented.h:400 [inline]
 __refcount_sub_and_test include/linux/refcount.h:389 [inline]
 __refcount_dec_and_test include/linux/refcount.h:432 [inline]
 refcount_dec_and_test include/linux/refcount.h:450 [inline]
 btrfs_put_root+0x2f/0x250 fs/btrfs/disk-io.c:1806
 btrfs_drop_and_free_fs_root+0x160/0x210 fs/btrfs/disk-io.c:4154
 btrfs_free_fs_roots+0x2f9/0x3c0 fs/btrfs/disk-io.c:1847
 close_ctree+0x798/0x12d0 fs/btrfs/disk-io.c:4442
 generic_shutdown_super+0x13d/0x2d0 fs/super.c:646
 kill_anon_super+0x3b/0x70 fs/super.c:1292
 btrfs_kill_super+0x41/0x50 fs/btrfs/super.c:2127
 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
 exit_task_work include/linux/task_work.h:40 [inline]
 do_exit+0x70f/0x22c0 kernel/exit.c:976
 do_group_exit+0x21b/0x2d0 kernel/exit.c:1119
 get_signal+0x1284/0x1330 kernel/signal.c:3037
 arch_do_signal_or_restart+0xbc/0x840 arch/x86/kernel/signal.c:337
 __exit_to_user_mode_loop kernel/entry/common.c:64 [inline]
 exit_to_user_mode_loop+0xa9/0x680 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:230 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:318 [inline]
 do_syscall_64+0x353/0x580 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fb71b99ce59
Code: Unable to access opcode bytes at 0x7fb71b99ce2f.
RSP: 002b:00007fb71c7fbfe8 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: fffffffffffffff2 RBX: 00007fb71bc16090 RCX: 00007fb71b99ce59
RDX: 0000200000000000 RSI: 00000000c400941b RDI: 0000000000000005
RBP: 00007fb71ba32d6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fb71bc16128 R14: 00007fb71bc16090 R15: 00007ffc6beb6878
 </TASK>

Allocated by task 5357:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __kmalloc_cache_noprof+0x31c/0x660 mm/slub.c:5420
 kmalloc_noprof include/linux/slab.h:950 [inline]
 kzalloc_noprof include/linux/slab.h:1188 [inline]
 btrfs_alloc_root+0x75/0x930 fs/btrfs/disk-io.c:611
 read_tree_root_path+0x127/0xb00 fs/btrfs/disk-io.c:976
 btrfs_read_tree_root+0x34/0x60 fs/btrfs/disk-io.c:1040
 create_reloc_root+0x6b3/0xcb0 fs/btrfs/relocation.c:677
 btrfs_init_reloc_root+0x244/0x4b0 fs/btrfs/relocation.c:744
 record_root_in_trans+0x2ab/0x350 fs/btrfs/transaction.c:461
 btrfs_record_root_in_trans+0x15c/0x180 fs/btrfs/transaction.c:507
 start_transaction+0x39c/0x1820 fs/btrfs/transaction.c:793
 btrfs_truncate fs/btrfs/inode.c:7901 [inline]
 btrfs_setsize fs/btrfs/inode.c:5459 [inline]
 btrfs_setattr+0xa47/0x12a0 fs/btrfs/inode.c:5494
 notify_change+0xc1a/0xf40 fs/attr.c:556
 do_truncate+0x1c2/0x250 fs/open.c:68
 handle_truncate fs/namei.c:4307 [inline]
 do_open fs/namei.c:4703 [inline]
 path_openat+0x2f89/0x3860 fs/namei.c:4858
 do_file_open+0x23e/0x4a0 fs/namei.c:4887
 do_sys_openat2+0x113/0x200 fs/open.c:1364
 do_sys_open fs/open.c:1370 [inline]
 __do_sys_openat fs/open.c:1386 [inline]
 __se_sys_openat fs/open.c:1381 [inline]
 __x64_sys_openat+0x138/0x170 fs/open.c:1381
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 5334:
 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:6251 [inline]
 kfree+0x1c5/0x640 mm/slub.c:6566
 __del_reloc_root+0x341/0x3b0 fs/btrfs/relocation.c:547
 free_reloc_roots+0x5f/0x90 fs/btrfs/relocation.c:1803
 merge_reloc_roots+0x73f/0x8a0 fs/btrfs/relocation.c:1888
 relocate_block_group+0xbcc/0xe70 fs/btrfs/relocation.c:3638
 do_nonremap_reloc+0xa8/0x5b0 fs/btrfs/relocation.c:5268
 btrfs_relocate_block_group+0x7e6/0xc40 fs/btrfs/relocation.c:5434
 btrfs_relocate_chunk+0x115/0x820 fs/btrfs/volumes.c:3598
 __btrfs_balance+0x1db0/0x2ae0 fs/btrfs/volumes.c:4509
 btrfs_balance+0xaf3/0x11b0 fs/btrfs/volumes.c:4896
 btrfs_ioctl_balance+0x3d3/0x610 fs/btrfs/ioctl.c:3453
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff888012bf8000
 which belongs to the cache kmalloc-4k of size 4096
The buggy address is located 1584 bytes inside of
 freed 4096-byte region [ffff888012bf8000, ffff888012bf9000)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x12bf8
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 ffff88801ac42140 dead000000000100 dead000000000122
raw: 0000000000000000 0000000800040004 00000000f5000000 0000000000000000
head: 00fff00000000040 ffff88801ac42140 dead000000000100 dead000000000122
head: 0000000000000000 0000000800040004 00000000f5000000 0000000000000000
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 Unmovable, gfp_mask 0xd2040(__GFP_IO|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 5098, tgid 5098 (getty), ts 52351460133, free_ts 50275728743
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x22d/0x280 mm/page_alloc.c:1853
 prep_new_page mm/page_alloc.c:1861 [inline]
 get_page_from_freelist+0x2593/0x2610 mm/page_alloc.c:3941
 __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5221
 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:7272
 refill_sheaf mm/slub.c:2816 [inline]
 __pcs_replace_empty_main+0x321/0x720 mm/slub.c:4652
 alloc_from_pcs mm/slub.c:4750 [inline]
 slab_alloc_node mm/slub.c:4884 [inline]
 __do_kmalloc_node mm/slub.c:5295 [inline]
 __kmalloc_noprof+0x474/0x760 mm/slub.c:5308
 kmalloc_noprof include/linux/slab.h:954 [inline]
 tomoyo_realpath_from_path+0xe3/0x5d0 security/tomoyo/realpath.c:251
 tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
 tomoyo_path_perm+0x283/0x560 security/tomoyo/file.c:827
 security_inode_getattr+0x12b/0x310 security/security.c:1895
 vfs_getattr fs/stat.c:259 [inline]
 vfs_fstat fs/stat.c:281 [inline]
 __do_sys_newfstat fs/stat.c:551 [inline]
 __se_sys_newfstat fs/stat.c:546 [inline]
 __x64_sys_newfstat+0x13b/0x270 fs/stat.c:546
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
page last free pid 5007 tgid 5007 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 __free_pages_prepare mm/page_alloc.c:1397 [inline]
 __free_frozen_pages+0xc1c/0xd30 mm/page_alloc.c:2938
 __slab_free+0x274/0x2c0 mm/slub.c:5613
 qlink_free mm/kasan/quarantine.c:163 [inline]
 qlist_free_all+0x99/0x100 mm/kasan/quarantine.c:179
 kasan_quarantine_reduce+0x148/0x160 mm/kasan/quarantine.c:286
 __kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:350
 kasan_slab_alloc include/linux/kasan.h:253 [inline]
 slab_post_alloc_hook mm/slub.c:4570 [inline]
 slab_alloc_node mm/slub.c:4899 [inline]
 kmem_cache_alloc_node_noprof+0x384/0x690 mm/slub.c:4951
 __alloc_skb+0x1d0/0x7d0 net/core/skbuff.c:702
 alloc_skb include/linux/skbuff.h:1385 [inline]
 nlmsg_new include/net/netlink.h:1055 [inline]
 netlink_ack+0x146/0xa50 net/netlink/af_netlink.c:2492
 netlink_rcv_skb+0x2b6/0x4b0 net/netlink/af_netlink.c:2561
 genl_rcv+0x28/0x40 net/netlink/genetlink.c:1218
 netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
 netlink_unicast+0x75c/0x8e0 net/netlink/af_netlink.c:1344
 netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1899
 sock_sendmsg_nosec net/socket.c:787 [inline]
 __sock_sendmsg net/socket.c:802 [inline]
 ____sys_sendmsg+0x972/0x9f0 net/socket.c:2698
 ___sys_sendmsg+0x2a5/0x360 net/socket.c:2752
 __sys_sendmsg net/socket.c:2784 [inline]
 __do_sys_sendmsg net/socket.c:2789 [inline]
 __se_sys_sendmsg net/socket.c:2787 [inline]
 __x64_sys_sendmsg+0x1bd/0x2a0 net/socket.c:2787
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94

Memory state around the buggy address:
 ffff888012bf8500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888012bf8580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888012bf8600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                     ^
 ffff888012bf8680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888012bf8700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (3):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/06/04 17:41 upstream ba3e43a9e601 197909be .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root KASAN: slab-use-after-free Write in btrfs_put_root
2026/05/30 20:14 upstream f5e5d3509bff 6b4a8443 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root KASAN: slab-use-after-free Write in btrfs_put_root
2026/05/24 05:27 upstream 4cbfe4502e3d c69befb3 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root KASAN: slab-use-after-free Write in btrfs_put_root
* Struck through repros no longer work on HEAD.