[syzbot] [btrfs?] KASAN: slab-use-after-free Read in add_delayed_ref

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: d61a00525464 Add linux-next specific files for 20241011
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=16f9a887980000
kernel config: https://syzkaller.appspot.com/x/.config?x=8554528c7f4bf3fb
dashboard link: https://syzkaller.appspot.com/bug?extid=c3a3a153f0190dca5be9
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=1266c727980000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17ce9440580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f615720e9964/disk-d61a0052.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/c4a45c7583c6/vmlinux-d61a0052.xz
kernel image: https://storage.googleapis.com/syzbot-assets/d767ab86d0d0/bzImage-d61a0052.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/e1c3551adc6e/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c3a3a1...@syzkaller.appspotmail.com

BTRFS info (device loop0): first mount of filesystem 395ef67a-297e-477c-816d-cd80a5b93e5d
BTRFS info (device loop0): using sha256 (sha256-avx2) checksum algorithm
BTRFS info (device loop0): using free-space-tree
==================================================================
BUG: KASAN: slab-use-after-free in add_delayed_ref+0x12ca/0x1e00 fs/btrfs/delayed-ref.c:1077
Read of size 8 at addr ffff888027c83570 by task syz-executor406/11166

CPU: 1 UID: 0 PID: 11166 Comm: syz-executor406 Not tainted 6.12.0-rc2-next-20241011-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:377 [inline]
print_report+0x169/0x550 mm/kasan/report.c:488
kasan_report+0x143/0x180 mm/kasan/report.c:601
add_delayed_ref+0x12ca/0x1e00 fs/btrfs/delayed-ref.c:1077
btrfs_alloc_tree_block+0xdfb/0x1440 fs/btrfs/extent-tree.c:5209
btrfs_force_cow_block+0x526/0x1da0 fs/btrfs/ctree.c:573
btrfs_cow_block+0x35e/0xa40 fs/btrfs/ctree.c:754
btrfs_search_slot+0xbdd/0x30d0 fs/btrfs/ctree.c:2116
btrfs_insert_empty_items+0x9c/0x1a0 fs/btrfs/ctree.c:4314
btrfs_create_new_inode+0xe27/0x1f60 fs/btrfs/inode.c:6344
btrfs_create_common+0x1d4/0x2e0 fs/btrfs/inode.c:6578
vfs_mkdir+0x2f9/0x4f0 fs/namei.c:4257
do_mkdirat+0x264/0x3a0 fs/namei.c:4280
__do_sys_mkdirat fs/namei.c:4295 [inline]
__se_sys_mkdirat fs/namei.c:4293 [inline]
__x64_sys_mkdirat+0x87/0xa0 fs/namei.c:4293
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f5219f05379
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 41 1d 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f5219eb3168 EFLAGS: 00000246 ORIG_RAX: 0000000000000102
RAX: ffffffffffffffda RBX: 00007f5219f8b6c8 RCX: 00007f5219f05379
RDX: 0000000000000000 RSI: 0000000020000200 RDI: 0000000000000005
RBP: 00007f5219f8b6c0 R08: 00007f5219eb36c0 R09: 0000000000000000
R10: 00007f5219eb36c0 R11: 0000000000000246 R12: 00007f5219f8b6cc
R13: 0000000000000016 R14: 00007fff9f716d90 R15: 00007fff9f716e78
</TASK>

Allocated by task 11166:
kasan_save_stack mm/kasan/common.c:47 [inline]
kasan_save_track+0x3f/0x80 mm/kasan/common.c:68
unpoison_slab_object mm/kasan/common.c:319 [inline]
__kasan_slab_alloc+0x66/0x80 mm/kasan/common.c:345
kasan_slab_alloc include/linux/kasan.h:250 [inline]
slab_post_alloc_hook mm/slub.c:4094 [inline]
slab_alloc_node mm/slub.c:4143 [inline]
kmem_cache_alloc_noprof+0x1d9/0x380 mm/slub.c:4150
add_delayed_ref+0x13a/0x1e00 fs/btrfs/delayed-ref.c:1020
btrfs_alloc_tree_block+0xdfb/0x1440 fs/btrfs/extent-tree.c:5209
btrfs_force_cow_block+0x526/0x1da0 fs/btrfs/ctree.c:573
btrfs_cow_block+0x35e/0xa40 fs/btrfs/ctree.c:754
btrfs_search_slot+0xbdd/0x30d0 fs/btrfs/ctree.c:2116
btrfs_insert_empty_items+0x9c/0x1a0 fs/btrfs/ctree.c:4314
btrfs_create_new_inode+0xe27/0x1f60 fs/btrfs/inode.c:6344
btrfs_create_common+0x1d4/0x2e0 fs/btrfs/inode.c:6578
vfs_mkdir+0x2f9/0x4f0 fs/namei.c:4257
do_mkdirat+0x264/0x3a0 fs/namei.c:4280
__do_sys_mkdirat fs/namei.c:4295 [inline]
__se_sys_mkdirat fs/namei.c:4293 [inline]
__x64_sys_mkdirat+0x87/0xa0 fs/namei.c:4293
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 55:
kasan_save_stack mm/kasan/common.c:47 [inline]
kasan_save_track+0x3f/0x80 mm/kasan/common.c:68
kasan_save_free_info+0x40/0x50 mm/kasan/generic.c:582
poison_slab_object mm/kasan/common.c:247 [inline]
__kasan_slab_free+0x59/0x70 mm/kasan/common.c:264
kasan_slab_free include/linux/kasan.h:233 [inline]
slab_free_hook mm/slub.c:2329 [inline]
slab_free mm/slub.c:4588 [inline]
kmem_cache_free+0x1a2/0x440 mm/slub.c:4690
btrfs_put_delayed_ref_head fs/btrfs/delayed-ref.h:358 [inline]
cleanup_ref_head fs/btrfs/extent-tree.c:1932 [inline]
__btrfs_run_delayed_refs+0x3d34/0x4680 fs/btrfs/extent-tree.c:2113
btrfs_run_delayed_refs+0xe3/0x2c0 fs/btrfs/extent-tree.c:2213
btrfs_commit_transaction+0x4be/0x3740 fs/btrfs/transaction.c:2197
btrfs_qgroup_rescan_worker+0x17ac/0x1c60 fs/btrfs/qgroup.c:3864
btrfs_work_helper+0x390/0xc50 fs/btrfs/async-thread.c:314
process_one_work kernel/workqueue.c:3229 [inline]
process_scheduled_works+0xa63/0x1850 kernel/workqueue.c:3310
worker_thread+0x870/0xd30 kernel/workqueue.c:3391
kthread+0x2f0/0x390 kernel/kthread.c:389
ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

The buggy address belongs to the object at ffff888027c83570
which belongs to the cache btrfs_delayed_ref_head of size 328
The buggy address is located 0 bytes inside of
freed 328-byte region [ffff888027c83570, ffff888027c836b8)

The buggy address belongs to the physical page:
page: refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x27c82
head: order:1 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 ffff88802fe6a000 ffffea0001ecef00 dead000000000004
raw: 0000000000000000 0000000080140014 00000001f5000000 0000000000000000
head: 00fff00000000040 ffff88802fe6a000 ffffea0001ecef00 dead000000000004
head: 0000000000000000 0000000080140014 00000001f5000000 0000000000000000
head: 00fff00000000001 ffffea00009f2081 ffffffffffffffff 0000000000000000
head: 0000000000000002 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 1, migratetype Unmovable, gfp_mask 0xd2040(__GFP_IO|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 5557, tgid 5556 (syz-executor406), ts 235052280151, free_ts 234997412486
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x1f3/0x230 mm/page_alloc.c:1537
prep_new_page mm/page_alloc.c:1545 [inline]
get_page_from_freelist+0x3129/0x3270 mm/page_alloc.c:3493
__alloc_pages_noprof+0x292/0x710 mm/page_alloc.c:4769
alloc_pages_mpol_noprof+0x3e8/0x680 mm/mempolicy.c:2265
alloc_slab_page+0x6a/0x120 mm/slub.c:2399
allocate_slab+0x5a/0x2f0 mm/slub.c:2565
new_slab mm/slub.c:2618 [inline]
___slab_alloc+0xcd1/0x14b0 mm/slub.c:3805
__slab_alloc+0x58/0xa0 mm/slub.c:3895
__slab_alloc_node mm/slub.c:3970 [inline]
slab_alloc_node mm/slub.c:4131 [inline]
kmem_cache_alloc_noprof+0x268/0x380 mm/slub.c:4150
add_delayed_ref+0x13a/0x1e00 fs/btrfs/delayed-ref.c:1020
btrfs_free_tree_block+0x354/0xd80 fs/btrfs/extent-tree.c:3455
btrfs_force_cow_block+0xf44/0x1da0 fs/btrfs/ctree.c:622
btrfs_cow_block+0x35e/0xa40 fs/btrfs/ctree.c:754
btrfs_search_slot+0xbdd/0x30d0 fs/btrfs/ctree.c:2116
btrfs_insert_empty_items+0x9c/0x1a0 fs/btrfs/ctree.c:4314
btrfs_create_new_inode+0xe27/0x1f60 fs/btrfs/inode.c:6344
page last free pid 5558 tgid 5558 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
free_pages_prepare mm/page_alloc.c:1108 [inline]
free_unref_page+0xcfb/0xf20 mm/page_alloc.c:2674
__slab_free+0x31b/0x3d0 mm/slub.c:4499
qlink_free mm/kasan/quarantine.c:163 [inline]
qlist_free_all+0x9a/0x140 mm/kasan/quarantine.c:179
kasan_quarantine_reduce+0x14f/0x170 mm/kasan/quarantine.c:286
__kasan_slab_alloc+0x23/0x80 mm/kasan/common.c:329
kasan_slab_alloc include/linux/kasan.h:250 [inline]
slab_post_alloc_hook mm/slub.c:4094 [inline]
slab_alloc_node mm/slub.c:4143 [inline]
kmem_cache_alloc_noprof+0x1d9/0x380 mm/slub.c:4150
getname_flags+0xb7/0x540 fs/namei.c:139
do_sys_openat2+0xd2/0x1d0 fs/open.c:1409
do_sys_open fs/open.c:1430 [inline]
__do_sys_openat fs/open.c:1446 [inline]
__se_sys_openat fs/open.c:1441 [inline]
__x64_sys_openat+0x247/0x2a0 fs/open.c:1441
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
ffff888027c83400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888027c83480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff888027c83500: fb fb fb fb fb fb fc fc fc fc fc fc fc fc fa fb
^
ffff888027c83580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff888027c83600: 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 syzk...@googlegroups.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.

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

[syzbot]

syzbot has bisected this issue to:

commit a3aad8f4f5d9d9a977ee5be32b07bcc083cc8d28
Author: Filipe Manana <fdma...@suse.com>
Date: Tue Sep 24 16:12:32 2024 +0000

btrfs: qgroups: remove bytenr field from struct btrfs_qgroup_extent_record

bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=14596887980000
start commit: d61a00525464 Add linux-next specific files for 20241011
git tree: linux-next
final oops: https://syzkaller.appspot.com/x/report.txt?x=16596887980000
console output: https://syzkaller.appspot.com/x/log.txt?x=12596887980000

kernel config: https://syzkaller.appspot.com/x/.config?x=8554528c7f4bf3fb
dashboard link: https://syzkaller.appspot.com/bug?extid=c3a3a153f0190dca5be9

syz repro: https://syzkaller.appspot.com/x/repro.syz?x=1266c727980000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17ce9440580000

Reported-by: syzbot+c3a3a1...@syzkaller.appspotmail.com
Fixes: a3aad8f4f5d9 ("btrfs: qgroups: remove bytenr field from struct btrfs_qgroup_extent_record")

For information about bisection process see: https://goo.gl/tpsmEJ#bisection

[Edward Adam Davis]

using delayed_refs->lock to sync btrfs_work_helper and add_delayed_ref

#syz test

diff --git a/fs/btrfs/delayed-ref.c b/fs/btrfs/delayed-ref.c
index 13c2e00d1270..cb57e65c9872 100644
--- a/fs/btrfs/delayed-ref.c
+++ b/fs/btrfs/delayed-ref.c
@@ -1058,7 +1058,6 @@ static int add_delayed_ref(struct btrfs_trans_handle *trans,
head_ref = new_head_ref;

merged = insert_delayed_ref(trans, head_ref, node);
- spin_unlock(&delayed_refs->lock);

/*
* Need to update the delayed_refs_rsv with any changes we may have
@@ -1073,8 +1072,12 @@ static int add_delayed_ref(struct btrfs_trans_handle *trans,
if (merged)
kmem_cache_free(btrfs_delayed_ref_node_cachep, node);

- if (qrecord_inserted)
- return btrfs_qgroup_trace_extent_post(trans, record, head_ref->bytenr);
+ if (qrecord_inserted) {
+ ret = btrfs_qgroup_trace_extent_post(trans, record, head_ref->bytenr);
+ spin_unlock(&delayed_refs->lock);
+ return ret;
+ }
+ spin_unlock(&delayed_refs->lock);
return 0;

free_record:

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
BUG: sleeping function called from invalid context in ulist_alloc

BTRFS info (device loop0): first mount of filesystem 395ef67a-297e-477c-816d-cd80a5b93e5d
BTRFS info (device loop0): using sha256 (sha256-avx2) checksum algorithm
BTRFS info (device loop0): using free-space-tree

BUG: sleeping function called from invalid context at include/linux/sched/mm.h:321
in_atomic(): 1, irqs_disabled(): 0, non_block: 0, pid: 6014, name: syz.0.15
preempt_count: 1, expected: 0
RCU nest depth: 0, expected: 0
8 locks held by syz.0.15/6014:
#0: ffff888032202420 (sb_writers#13){.+.+}-{0:0}, at: mnt_want_write+0x3f/0x90 fs/namespace.c:515
#1: ffff888066478d90 (&type->i_mutex_dir_key#8/1){+.+.}-{3:3}, at: inode_lock_nested include/linux/fs.h:851 [inline]
#1: ffff888066478d90 (&type->i_mutex_dir_key#8/1){+.+.}-{3:3}, at: filename_create+0x260/0x540 fs/namei.c:4026
#2: ffff888032202610 (sb_internal#2){.+.+}-{0:0}, at: btrfs_create_common+0x1b2/0x2e0 fs/btrfs/inode.c:6572
#3: ffff88802e9ce458 (btrfs_trans_num_writers){++++}-{0:0}, at: join_transaction+0x15e/0xd70 fs/btrfs/transaction.c:313
#4: ffff88802e9ce480 (btrfs_trans_num_extwriters){++++}-{0:0}, at: join_transaction+0x15e/0xd70 fs/btrfs/transaction.c:313
#5: ffff888078a220f8 (btrfs-tree-01){++++}-{3:3}, at: btrfs_tree_lock_nested+0x2f/0x250 fs/btrfs/locking.c:189
#6: ffff8880302980f8 (btrfs-tree-01/1){+.+.}-{3:3}, at: btrfs_tree_lock_nested+0x2f/0x250 fs/btrfs/locking.c:189
#7: ffff88802174d388 (&cur_trans->delayed_refs.lock){+.+.}-{2:2}, at: spin_lock include/linux/spinlock.h:351 [inline]
#7: ffff88802174d388 (&cur_trans->delayed_refs.lock){+.+.}-{2:2}, at: add_delayed_ref+0x6e6/0x1e70 fs/btrfs/delayed-ref.c:1045
Preemption disabled at:
[<0000000000000000>] 0x0
CPU: 0 UID: 0 PID: 6014 Comm: syz.0.15 Not tainted 6.12.0-rc3-next-20241015-syzkaller-04439-gb852e1e7a038-dirty #0

Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120

__might_resched+0x5d4/0x780 kernel/sched/core.c:8653
might_alloc include/linux/sched/mm.h:321 [inline]
slab_pre_alloc_hook mm/slub.c:4045 [inline]
slab_alloc_node mm/slub.c:4123 [inline]
__kmalloc_cache_noprof+0x61/0x390 mm/slub.c:4299
kmalloc_noprof include/linux/slab.h:879 [inline]
ulist_alloc+0x6e/0x140 fs/btrfs/ulist.c:101
btrfs_find_all_roots_safe+0xf3/0x4c0 fs/btrfs/backref.c:1748
btrfs_find_all_roots+0x84/0xf0 fs/btrfs/backref.c:1799
btrfs_qgroup_trace_extent_post+0x1cd/0x2e0 fs/btrfs/qgroup.c:2105
add_delayed_ref+0x131c/0x1e70 fs/btrfs/delayed-ref.c:1076

btrfs_alloc_tree_block+0xdfb/0x1440 fs/btrfs/extent-tree.c:5209
btrfs_force_cow_block+0x526/0x1da0 fs/btrfs/ctree.c:573
btrfs_cow_block+0x35e/0xa40 fs/btrfs/ctree.c:754
btrfs_search_slot+0xbdd/0x30d0 fs/btrfs/ctree.c:2116
btrfs_insert_empty_items+0x9c/0x1a0 fs/btrfs/ctree.c:4314
btrfs_create_new_inode+0xe27/0x1f60 fs/btrfs/inode.c:6344
btrfs_create_common+0x1d4/0x2e0 fs/btrfs/inode.c:6578
vfs_mkdir+0x2f9/0x4f0 fs/namei.c:4257
do_mkdirat+0x264/0x3a0 fs/namei.c:4280
__do_sys_mkdirat fs/namei.c:4295 [inline]
__se_sys_mkdirat fs/namei.c:4293 [inline]
__x64_sys_mkdirat+0x87/0xa0 fs/namei.c:4293
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x77/0x7f

RIP: 0033:0x7f8dcbd7dff9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 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:00007f8dccb5c038 EFLAGS: 00000246 ORIG_RAX: 0000000000000102
RAX: ffffffffffffffda RBX: 00007f8dcbf35f80 RCX: 00007f8dcbd7dff9

RDX: 0000000000000000 RSI: 0000000020000200 RDI: 0000000000000005

RBP: 00007f8dcbdf0296 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 00007f8dcbf35f80 R15: 00007ffe00c6dd48
</TASK>


Tested on:

commit: b852e1e7 Add linux-next specific files for 20241015
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1186d727980000
kernel config: https://syzkaller.appspot.com/x/.config?x=3cb0191818709a2b

dashboard link: https://syzkaller.appspot.com/bug?extid=c3a3a153f0190dca5be9
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

patch: https://syzkaller.appspot.com/x/patch.diff?x=12c2045f980000

[Edward Adam Davis]

move head_ref->bytenr to the protection range of delayed_refs->lock

#syz test

diff --git a/fs/btrfs/delayed-ref.c b/fs/btrfs/delayed-ref.c

index 13c2e00d1270..f50fc05847a1 100644
--- a/fs/btrfs/delayed-ref.c
+++ b/fs/btrfs/delayed-ref.c
@@ -1012,6 +1012,7 @@ static int add_delayed_ref(struct btrfs_trans_handle *trans,
int action = generic_ref->action;
bool merged;
int ret;
+ u64 bytenr;

node = kmem_cache_alloc(btrfs_delayed_ref_node_cachep, GFP_NOFS);
if (!node)
@@ -1056,6 +1057,7 @@ static int add_delayed_ref(struct btrfs_trans_handle *trans,
goto free_record;
}
head_ref = new_head_ref;
+ bytenr = head_ref->bytenr;

merged = insert_delayed_ref(trans, head_ref, node);

spin_unlock(&delayed_refs->lock);
@@ -1074,7 +1076,7 @@ static int add_delayed_ref(struct btrfs_trans_handle *trans,
kmem_cache_free(btrfs_delayed_ref_node_cachep, node);

if (qrecord_inserted)
- return btrfs_qgroup_trace_extent_post(trans, record, head_ref->bytenr);

+ return btrfs_qgroup_trace_extent_post(trans, record, bytenr);
return 0;

free_record:

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+c3a3a1...@syzkaller.appspotmail.com
Tested-by: syzbot+c3a3a1...@syzkaller.appspotmail.com

Tested on:

commit: b852e1e7 Add linux-next specific files for 20241015
git tree: linux-next

console output: https://syzkaller.appspot.com/x/log.txt?x=143ec030580000

kernel config: https://syzkaller.appspot.com/x/.config?x=3cb0191818709a2b
dashboard link: https://syzkaller.appspot.com/bug?extid=c3a3a153f0190dca5be9
compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

patch: https://syzkaller.appspot.com/x/patch.diff?x=16ced727980000

Note: testing is done by a robot and is best-effort only.

[Edward Adam Davis]

This is because the thread routine btrfs_work_helper released head_def after
exiting delayed_refs->lock in add_delayed_ref.
Causing add_delayed_ref to encounter uaf when accessing head_def->bytenr
outside the delayed_refs->lock.

Move head_ref->bytenr into the protection range of delayed_refs->lock
to avoid uaf in add_delayed_ref.

Fixes: a3aad8f4f5d9 ("btrfs: qgroups: remove bytenr field from struct btrfs_qgroup_extent_record")

Reported-and-tested-by: syzbot+c3a3a1...@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=c3a3a153f0190dca5be9
Signed-off-by: Edward Adam Davis <ead...@qq.com>
---
fs/btrfs/delayed-ref.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

--
2.43.0

[Filipe Manana]

On Tue, Oct 15, 2024 at 1:40 PM Edward Adam Davis <ead...@qq.com> wrote:
>
> This is because the thread routine btrfs_work_helper released head_def after
> exiting delayed_refs->lock in add_delayed_ref.

This should be explained a lot better. Starting the changelog with
"This is because..." is odd. It should explain why the head reference
was freed (because delayed references were run).

> Causing add_delayed_ref to encounter uaf when accessing head_def->bytenr
> outside the delayed_refs->lock.
>
> Move head_ref->bytenr into the protection range of delayed_refs->lock
> to avoid uaf in add_delayed_ref.

This was already fixed yesterday, in a simpler way and with an
explanation of what's going on to trigger the use-after-free:

https://lore.kernel.org/linux-btrfs/02fc507b62b19be2348fc08de8b13bd7...@suse.com/

Thanks.

[David Sterba]

On Tue, Oct 15, 2024 at 01:49:04PM +0100, Filipe Manana wrote:
> On Tue, Oct 15, 2024 at 1:40 PM Edward Adam Davis <ead...@qq.com> wrote:
> >
> > This is because the thread routine btrfs_work_helper released head_def after
> > exiting delayed_refs->lock in add_delayed_ref.
>
> This should be explained a lot better. Starting the changelog with
> "This is because..." is odd. It should explain why the head reference
> was freed (because delayed references were run).
>
> > Causing add_delayed_ref to encounter uaf when accessing head_def->bytenr
> > outside the delayed_refs->lock.
> >
> > Move head_ref->bytenr into the protection range of delayed_refs->lock
> > to avoid uaf in add_delayed_ref.
>
>
> This was already fixed yesterday, in a simpler way and with an
> explanation of what's going on to trigger the use-after-free:
>
> https://lore.kernel.org/linux-btrfs/02fc507b62b19be2348fc08de8b13bd7...@suse.com/

This will be in the upcoming linux-next, so we'll not get the syzbot and
build reports anymore.

[syzbot]

Auto-closing this bug as obsolete.
No recent activity, existing reproducers are no longer triggering the issue.