syzbot


KASAN: slab-use-after-free Write in __bch2_trans_commit

Status: moderation: reported on 2025/06/21 05:50
Subsystems: bcachefs
[Documentation on labels]
Reported-by: syzbot+c475a3db5f80f660f0e8@syzkaller.appspotmail.com
First crash: 4d10h, last: 1d04h

Sample crash report:
    journal_seq_nonempty 0
    journal_seq_empty    0
    need_discard         0
    need_inc_gen         0
    dirty_sectors        256
    stripe_sectors       0
    cached_sectors       0
    stripe               0
    stripe_redundancy    0
    io_time[READ]        0
    io_time[WRITE]       0
    fragmentation     0
    bp_start          8
  
  incorrectly set at freespace:0:42:0 (free 0, genbits 0 should be 0), fixing
bcachefs (loop0): u64s 13 type alloc_v4 0:34:0 len 0 ver 0: 
    gen 0 oldest_gen 0 data_type user
    journal_seq_nonempty 0
    journal_seq_empty    0
    need_discard         0
    need_inc_gen         0
    dirty_sectors        16
    stripe_sectors       0
    cached_sectors       0
    stripe               0
    stripe_redundancy    0
    io_time[READ]        0
    io_time[WRITE]       0
    fragmentation     134217728
    bp_start          8
  
  incorrectly set at freespace:0:34:0 (free 0, genbits 0 should be 0), fixing
bcachefs (loop0): u64s 13 type alloc_v4 0:42:0 len 0 ver 0: 
    gen 0 oldest_gen 0 data_type btree
    journal_seq_nonempty 0
    journal_seq_empty    0
    need_discard         0
    need_inc_gen         0
    dirty_sectors        256
    stripe_sectors       0
    cached_sectors       0
    stripe               0
    stripe_redundancy    0
    io_time[READ]        0
    io_time[WRITE]       0
    fragmentation     0
    bp_start          8
  
  incorrectly set at freespace:0:42:0 (free 0, genbits 0 should be 0), fixing
==================================================================
BUG: KASAN: slab-use-after-free in journal_entry_init fs/bcachefs/journal.h:217 [inline]
BUG: KASAN: slab-use-after-free in bch2_journal_add_entry fs/bcachefs/journal.h:242 [inline]
BUG: KASAN: slab-use-after-free in bch2_journal_res_put fs/bcachefs/journal.h:320 [inline]
BUG: KASAN: slab-use-after-free in do_bch2_trans_commit fs/bcachefs/btree_trans_commit.c:868 [inline]
BUG: KASAN: slab-use-after-free in __bch2_trans_commit+0x359e/0x8880 fs/bcachefs/btree_trans_commit.c:1079
Write of size 8 at addr ffff888054d90000 by task syz.0.0/5345

CPU: 0 UID: 0 PID: 5345 Comm: syz.0.0 Not tainted 6.16.0-rc2-syzkaller-00162-g41687a5c6f8b #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:408 [inline]
 print_report+0xd2/0x2b0 mm/kasan/report.c:521
 kasan_report+0x118/0x150 mm/kasan/report.c:634
 journal_entry_init fs/bcachefs/journal.h:217 [inline]
 bch2_journal_add_entry fs/bcachefs/journal.h:242 [inline]
 bch2_journal_res_put fs/bcachefs/journal.h:320 [inline]
 do_bch2_trans_commit fs/bcachefs/btree_trans_commit.c:868 [inline]
 __bch2_trans_commit+0x359e/0x8880 fs/bcachefs/btree_trans_commit.c:1079
 bch2_trans_commit fs/bcachefs/btree_update.h:242 [inline]
 bch2_journal_replay+0x1789/0x2620 fs/bcachefs/recovery.c:396
 bch2_run_recovery_pass fs/bcachefs/recovery_passes.c:485 [inline]
 __bch2_run_recovery_passes+0x395/0x1010 fs/bcachefs/recovery_passes.c:540
 bch2_run_recovery_passes+0x184/0x210 fs/bcachefs/recovery_passes.c:611
 bch2_fs_recovery+0x25fd/0x3950 fs/bcachefs/recovery.c:989
 bch2_fs_start+0xa99/0xd90 fs/bcachefs/super.c:1203
 bch2_fs_get_tree+0xb02/0x14f0 fs/bcachefs/fs.c:2489
 vfs_get_tree+0x8f/0x2b0 fs/super.c:1804
 do_new_mount+0x24a/0xa40 fs/namespace.c:3885
 do_mount fs/namespace.c:4222 [inline]
 __do_sys_mount fs/namespace.c:4433 [inline]
 __se_sys_mount+0x317/0x410 fs/namespace.c:4410
 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
RIP: 0033:0x7f947a3900ca
Code: d8 64 89 02 48 c7 c0 ff ff ff ff eb a6 e8 de 1a 00 00 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 49 89 ca b8 a5 00 00 00 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:00007f94767f4e68 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007f94767f4ef0 RCX: 00007f947a3900ca
RDX: 00002000000000c0 RSI: 0000200000000000 RDI: 00007f94767f4eb0
RBP: 00002000000000c0 R08: 00007f94767f4ef0 R09: 0000000000810000
R10: 0000000000810000 R11: 0000000000000246 R12: 0000200000000000
R13: 00007f94767f4eb0 R14: 0000000000005991 R15: 0000200000000280
 </TASK>

Allocated by task 38:
 kasan_save_stack mm/kasan/common.c:47 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
 unpoison_slab_object mm/kasan/common.c:319 [inline]
 __kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:345
 kasan_slab_alloc include/linux/kasan.h:250 [inline]
 slab_post_alloc_hook mm/slub.c:4148 [inline]
 slab_alloc_node mm/slub.c:4197 [inline]
 kmem_cache_alloc_node_noprof+0x1bb/0x3c0 mm/slub.c:4249
 kmalloc_reserve+0xbd/0x290 net/core/skbuff.c:579
 __alloc_skb+0x142/0x2d0 net/core/skbuff.c:670
 alloc_skb include/linux/skbuff.h:1336 [inline]
 nlmsg_new include/net/netlink.h:1041 [inline]
 inet6_rt_notify+0x165/0x430 net/ipv6/route.c:6334
 fib6_add_rt2node+0x1876/0x33a0 net/ipv6/ip6_fib.c:1282
 fib6_add+0x8da/0x18a0 net/ipv6/ip6_fib.c:1535
 __ip6_ins_rt net/ipv6/route.c:1351 [inline]
 ip6_ins_rt+0xc8/0x120 net/ipv6/route.c:1361
 __ipv6_ifa_notify+0x63f/0xac0 net/ipv6/addrconf.c:6286
 ipv6_ifa_notify net/ipv6/addrconf.c:6325 [inline]
 addrconf_dad_completed+0x180/0xd60 net/ipv6/addrconf.c:4324
 addrconf_dad_work+0xc36/0x14b0 net/ipv6/addrconf.c:-1
 process_one_work kernel/workqueue.c:3238 [inline]
 process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3321
 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3402
 kthread+0x70e/0x8a0 kernel/kthread.c:464
 ret_from_fork+0x3f9/0x770 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Freed by task 38:
 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:2381 [inline]
 slab_free mm/slub.c:4643 [inline]
 kmem_cache_free+0x18f/0x400 mm/slub.c:4745
 skb_release_data+0x62d/0x7c0 net/core/skbuff.c:1087
 skb_release_all net/core/skbuff.c:1152 [inline]
 __kfree_skb net/core/skbuff.c:1166 [inline]
 consume_skb+0x9e/0xf0 net/core/skbuff.c:1398
 netlink_broadcast_filtered+0x103c/0x1140 net/netlink/af_netlink.c:1524
 nlmsg_multicast_filtered include/net/netlink.h:1151 [inline]
 nlmsg_multicast include/net/netlink.h:1170 [inline]
 nlmsg_notify+0xf0/0x1a0 net/netlink/af_netlink.c:2577
 fib6_add_rt2node+0x1876/0x33a0 net/ipv6/ip6_fib.c:1282
 fib6_add+0x8da/0x18a0 net/ipv6/ip6_fib.c:1535
 __ip6_ins_rt net/ipv6/route.c:1351 [inline]
 ip6_ins_rt+0xc8/0x120 net/ipv6/route.c:1361
 __ipv6_ifa_notify+0x63f/0xac0 net/ipv6/addrconf.c:6286
 ipv6_ifa_notify net/ipv6/addrconf.c:6325 [inline]
 addrconf_dad_completed+0x180/0xd60 net/ipv6/addrconf.c:4324
 addrconf_dad_work+0xc36/0x14b0 net/ipv6/addrconf.c:-1
 process_one_work kernel/workqueue.c:3238 [inline]
 process_scheduled_works+0xae1/0x17b0 kernel/workqueue.c:3321
 worker_thread+0x8a0/0xda0 kernel/workqueue.c:3402
 kthread+0x70e/0x8a0 kernel/kthread.c:464
 ret_from_fork+0x3f9/0x770 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

The buggy address belongs to the object at ffff888054d90000
 which belongs to the cache skbuff_small_head of size 704
The buggy address is located 0 bytes inside of
 freed 704-byte region [ffff888054d90000, ffff888054d902c0)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x54d90
head: order:2 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0x4fff00000000040(head|node=1|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 04fff00000000040 ffff88801c283dc0 dead000000000122 0000000000000000
raw: 0000000000000000 0000000000130013 00000000f5000000 0000000000000000
head: 04fff00000000040 ffff88801c283dc0 dead000000000122 0000000000000000
head: 0000000000000000 0000000000130013 00000000f5000000 0000000000000000
head: 04fff00000000002 ffffea0001536401 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000004
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 2, migratetype Unmovable, gfp_mask 0xd2820(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 38, tgid 38 (kworker/u4:3), ts 145478912315, free_ts 145443190565
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x240/0x2a0 mm/page_alloc.c:1704
 prep_new_page mm/page_alloc.c:1712 [inline]
 get_page_from_freelist+0x21e4/0x22c0 mm/page_alloc.c:3669
 __alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:4959
 alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2419
 alloc_slab_page mm/slub.c:2451 [inline]
 allocate_slab+0x8a/0x3b0 mm/slub.c:2619
 new_slab mm/slub.c:2673 [inline]
 ___slab_alloc+0xbfc/0x1480 mm/slub.c:3859
 __slab_alloc mm/slub.c:3949 [inline]
 __slab_alloc_node mm/slub.c:4024 [inline]
 slab_alloc_node mm/slub.c:4185 [inline]
 kmem_cache_alloc_node_noprof+0x280/0x3c0 mm/slub.c:4249
 kmalloc_reserve+0xbd/0x290 net/core/skbuff.c:579
 __alloc_skb+0x142/0x2d0 net/core/skbuff.c:670
 alloc_skb include/linux/skbuff.h:1336 [inline]
 nlmsg_new include/net/netlink.h:1041 [inline]
 inet6_rt_notify+0x165/0x430 net/ipv6/route.c:6334
 fib6_add_rt2node+0x1876/0x33a0 net/ipv6/ip6_fib.c:1282
 fib6_add+0x8da/0x18a0 net/ipv6/ip6_fib.c:1535
 __ip6_ins_rt net/ipv6/route.c:1351 [inline]
 ip6_ins_rt+0xc8/0x120 net/ipv6/route.c:1361
 __ipv6_ifa_notify+0x63f/0xac0 net/ipv6/addrconf.c:6286
 ipv6_ifa_notify net/ipv6/addrconf.c:6325 [inline]
 addrconf_dad_completed+0x180/0xd60 net/ipv6/addrconf.c:4324
 addrconf_dad_work+0xc36/0x14b0 net/ipv6/addrconf.c:-1
page last free pid 5345 tgid 5344 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1248 [inline]
 __free_frozen_pages+0xc71/0xe70 mm/page_alloc.c:2706
 stack_depot_save_flags+0x445/0x900 lib/stackdepot.c:678
 kasan_save_stack mm/kasan/common.c:48 [inline]
 kasan_save_track+0x4f/0x80 mm/kasan/common.c:68
 unpoison_slab_object mm/kasan/common.c:319 [inline]
 __kasan_slab_alloc+0x6c/0x80 mm/kasan/common.c:345
 kasan_slab_alloc include/linux/kasan.h:250 [inline]
 slab_post_alloc_hook mm/slub.c:4148 [inline]
 slab_alloc_node mm/slub.c:4197 [inline]
 kmem_cache_alloc_noprof+0x1c1/0x3c0 mm/slub.c:4204
 __bkey_cached_alloc fs/bcachefs/btree_key_cache.c:136 [inline]
 bkey_cached_alloc fs/bcachefs/btree_key_cache.c:162 [inline]
 btree_key_cache_create fs/bcachefs/btree_key_cache.c:231 [inline]
 btree_key_cache_fill+0x45b/0x3010 fs/bcachefs/btree_key_cache.c:344
 bch2_btree_path_traverse_cached+0xc5d/0x10d0 fs/bcachefs/btree_key_cache.c:399
 bch2_btree_path_traverse_one+0x372/0x21d0 fs/bcachefs/btree_iter.c:1179
 bch2_btree_path_traverse fs/bcachefs/btree_iter.h:250 [inline]
 bch2_btree_iter_peek_slot+0x74e/0x1fa0 fs/bcachefs/btree_iter.c:2781
 __bch2_bkey_get_iter fs/bcachefs/btree_iter.h:632 [inline]
 bch2_bkey_get_iter fs/bcachefs/btree_iter.h:646 [inline]
 bch2_check_discard_freespace_key+0x20c/0xce0 fs/bcachefs/alloc_background.c:1414
 try_alloc_bucket fs/bcachefs/alloc_foreground.c:272 [inline]
 bch2_bucket_alloc_freelist fs/bcachefs/alloc_foreground.c:420 [inline]
 bch2_bucket_alloc_trans+0x1333/0x2410 fs/bcachefs/alloc_foreground.c:544
 bch2_bucket_alloc_set_trans+0x5a6/0xe70 fs/bcachefs/alloc_foreground.c:728
 __open_bucket_add_buckets+0x1437/0x1e40 fs/bcachefs/alloc_foreground.c:925
 open_bucket_add_buckets+0x2ee/0x440 fs/bcachefs/alloc_foreground.c:957
 bch2_alloc_sectors_start_trans+0xd26/0x1e80 fs/bcachefs/alloc_foreground.c:-1
 __bch2_btree_node_alloc fs/bcachefs/btree_update_interior.c:320 [inline]
 bch2_btree_reserve_get+0x641/0x1810 fs/bcachefs/btree_update_interior.c:534

Memory state around the buggy address:
 ffff888054d8ff00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff888054d8ff80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff888054d90000: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                   ^
 ffff888054d90080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888054d90100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2025/06/20 11:05 upstream 41687a5c6f8b ed3e87f7 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root KASAN: slab-use-after-free Write in __bch2_trans_commit
2025/06/17 05:43 upstream 9afe652958c3 cfebc887 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root KASAN: slab-use-after-free Write in __bch2_trans_commit
* Struck through repros no longer work on HEAD.