[syzbot] [bcachefs?] KASAN: slab-out-of-bounds Read in bch2_btree_node_read_done

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 083fc6d7fa0d Merge tag 'sched-urgent-2025-09-26' of git://..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=16fbe2e2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f5b21423ca3f0a96
dashboard link: https://syzkaller.appspot.com/bug?extid=ba71155d3eacc8f42477
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16433d34580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13e79f12580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/198ae77e2418/disk-083fc6d7.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/3d3f065fd75c/vmlinux-083fc6d7.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e65812e9d7b0/bzImage-083fc6d7.xz
mounted in repro: https://storage.googleapis.com/syzbot-assets/5219cf8dcb94/mount_0.gz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ba7115...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-out-of-bounds in bch2_btree_node_read_done+0x950/0x5550 fs/bcachefs/btree_io.c:1128
Read of size 8 at addr ffff88805874a010 by task syz.0.17/6055

CPU: 0 UID: 0 PID: 6055 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT_{RT,(full)}
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
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/0x240 mm/kasan/report.c:482
kasan_report+0x118/0x150 mm/kasan/report.c:595
bch2_btree_node_read_done+0x950/0x5550 fs/bcachefs/btree_io.c:1128
btree_node_read_work+0x40e/0xe60 fs/bcachefs/btree_io.c:1440
bch2_btree_node_read+0x887/0x2a00 fs/bcachefs/btree_io.c:-1
__bch2_btree_root_read fs/bcachefs/btree_io.c:1906 [inline]
bch2_btree_root_read+0x5f0/0x760 fs/bcachefs/btree_io.c:1928
read_btree_roots+0x2c6/0x840 fs/bcachefs/recovery.c:615
bch2_fs_recovery+0x261f/0x3a50 fs/bcachefs/recovery.c:1006
bch2_fs_start+0xaaf/0xda0 fs/bcachefs/super.c:1213
bch2_fs_get_tree+0xb39/0x1520 fs/bcachefs/fs.c:2488
vfs_get_tree+0x8f/0x2b0 fs/super.c:1815
do_new_mount+0x2a2/0x9e0 fs/namespace.c:3808
do_mount fs/namespace.c:4136 [inline]
__do_sys_mount fs/namespace.c:4347 [inline]
__se_sys_mount+0x317/0x410 fs/namespace.c:4324
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: 0033:0x7feb1599066a
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:00007ffe09e19a98 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: ffffffffffffffda RBX: 00007ffe09e19b20 RCX: 00007feb1599066a
RDX: 00002000000058c0 RSI: 0000200000000000 RDI: 00007ffe09e19ae0
RBP: 00002000000058c0 R08: 00007ffe09e19b20 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000200000000000
R13: 00007ffe09e19ae0 R14: 00000000000058f2 R15: 0000200000000180
</TASK>

Allocated by task 6055:
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:388 [inline]
__kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:405
kasan_kmalloc include/linux/kasan.h:260 [inline]
__do_kmalloc_node mm/slub.c:4376 [inline]
__kvmalloc_node_noprof+0x28d/0x550 mm/slub.c:5067
btree_node_data_alloc+0xdc/0x270 fs/bcachefs/btree_cache.c:151
__bch2_btree_node_mem_alloc+0x1dc/0x2e0 fs/bcachefs/btree_cache.c:193
bch2_fs_btree_cache_init+0x314/0x880 fs/bcachefs/btree_cache.c:653
bch2_fs_alloc fs/bcachefs/super.c:998 [inline]
bch2_fs_open+0x1da6/0x26e0 fs/bcachefs/super.c:2433
bch2_fs_get_tree+0x44f/0x1520 fs/bcachefs/fs.c:2472
vfs_get_tree+0x8f/0x2b0 fs/super.c:1815
do_new_mount+0x2a2/0x9e0 fs/namespace.c:3808
do_mount fs/namespace.c:4136 [inline]
__do_sys_mount fs/namespace.c:4347 [inline]
__se_sys_mount+0x317/0x410 fs/namespace.c:4324
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 ffff888058748000
which belongs to the cache kmalloc-rcl-8k of size 8192
The buggy address is located 16 bytes to the right of
allocated 8192-byte region [ffff888058748000, ffff88805874a000)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x58748
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
memcg:ffff8880273c6ce1
flags: 0x80000000000040(head|node=0|zone=1)
page_type: f5(slab)
raw: 0080000000000040 ffff8880198483c0 dead000000000122 0000000000000000
raw: 0000000000000000 0000000080020002 00000000f5000000 ffff8880273c6ce1
head: 0080000000000040 ffff8880198483c0 dead000000000122 0000000000000000
head: 0000000000000000 0000000080020002 00000000f5000000 ffff8880273c6ce1
head: 0080000000000003 ffffea000161d201 00000000ffffffff 00000000ffffffff
head: 0000000000000000 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 0x528d0(GFP_NOWAIT|__GFP_RECLAIMABLE|__GFP_IO|__GFP_FS|__GFP_NORETRY|__GFP_COMP), pid 6055, tgid 6055 (syz.0.17), ts 114481807879, free_ts 0
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+0x2119/0x21b0 mm/page_alloc.c:3858
__alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5148
alloc_pages_mpol+0xd1/0x380 mm/mempolicy.c:2416
alloc_slab_page mm/slub.c:2492 [inline]
allocate_slab+0x8a/0x370 mm/slub.c:2660
new_slab mm/slub.c:2714 [inline]
___slab_alloc+0x8d1/0xdc0 mm/slub.c:3901
__slab_alloc mm/slub.c:3992 [inline]
__slab_alloc_node mm/slub.c:4067 [inline]
slab_alloc_node mm/slub.c:4228 [inline]
__do_kmalloc_node mm/slub.c:4375 [inline]
__kvmalloc_node_noprof+0x1d6/0x550 mm/slub.c:5067
btree_node_data_alloc+0xdc/0x270 fs/bcachefs/btree_cache.c:151
__bch2_btree_node_mem_alloc+0x1dc/0x2e0 fs/bcachefs/btree_cache.c:193
bch2_fs_btree_cache_init+0x314/0x880 fs/bcachefs/btree_cache.c:653
bch2_fs_alloc fs/bcachefs/super.c:998 [inline]
bch2_fs_open+0x1da6/0x26e0 fs/bcachefs/super.c:2433
bch2_fs_get_tree+0x44f/0x1520 fs/bcachefs/fs.c:2472
vfs_get_tree+0x8f/0x2b0 fs/super.c:1815
do_new_mount+0x2a2/0x9e0 fs/namespace.c:3808
do_mount fs/namespace.c:4136 [inline]
__do_sys_mount fs/namespace.c:4347 [inline]
__se_sys_mount+0x317/0x410 fs/namespace.c:4324
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
page_owner free stack trace missing

Memory state around the buggy address:
ffff888058749f00: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff888058749f80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff88805874a000: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
^
ffff88805874a080: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88805874a100: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


---
This report is generated by a bot. It may contain errors.
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#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.

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If you want to undo deduplication, reply with:
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[syzbot]

Hello,

syzbot tried to test the proposed patch but the build/boot failed:

failed to apply patch:
can't find file to patch at input line 5
Perhaps you used the wrong -p or --strip option?
The text leading up to this was:
--------------------------
|diff --git a/fs/bcachefs/btree_io.c b/fs/bcachefs/btree_io.c
|index 590cd29f3e86..ab14fff1452f 100644
|--- a/fs/bcachefs/btree_io.c
|+++ b/fs/bcachefs/btree_io.c
--------------------------
No file to patch. Skipping patch.
1 out of 1 hunk ignored



Tested on:

commit: 30d4efb2 Merge tag 'for-linus-6.18-rc1-tag' of git://g..
git tree: upstream

kernel config: https://syzkaller.appspot.com/x/.config?x=f5b21423ca3f0a96
dashboard link: https://syzkaller.appspot.com/bug?extid=ba71155d3eacc8f42477
compiler:

patch: https://syzkaller.appspot.com/x/patch.diff?x=16afc334580000

[Edward Adam Davis]

#syz test

diff --git a/fs/bcachefs/btree_io.c b/fs/bcachefs/btree_io.c
index 590cd29f3e86..ab14fff1452f 100644
--- a/fs/bcachefs/btree_io.c
+++ b/fs/bcachefs/btree_io.c

@@ -1087,6 +1087,13 @@ int bch2_btree_node_read_done(struct bch_fs *c, struct bch_dev *ca,
"bad magic: want %llx, got %llx",
bset_magic(c), le64_to_cpu(b->data->magic));

+ btree_err_on(ptr_written >= btree_sectors(c),
+ -BCH_ERR_btree_node_read_err_must_retry,
+ c, ca, b, NULL, NULL,
+ btree_node_bad_magic,
+ "wrong written %u, btree sectors is %lu",
+ ptr_written, btree_sectors(c));
+
if (b->key.k.type == KEY_TYPE_btree_ptr_v2) {
struct bch_btree_ptr_v2 *bp =
&bkey_i_to_btree_ptr_v2(&b->key)->v;

[Edward Adam Davis]

#syz test: upstream 083fc6d7fa0d

[syzbot]

Hello,

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

Reported-by: syzbot+ba7115...@syzkaller.appspotmail.com
Tested-by: syzbot+ba7115...@syzkaller.appspotmail.com

Tested on:

commit: 083fc6d7 Merge tag 'sched-urgent-2025-09-26' of git://..
git tree: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
console output: https://syzkaller.appspot.com/x/log.txt?x=12d02334580000

kernel config: https://syzkaller.appspot.com/x/.config?x=f5b21423ca3f0a96
dashboard link: https://syzkaller.appspot.com/bug?extid=ba71155d3eacc8f42477

compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

patch: https://syzkaller.appspot.com/x/patch.diff?x=137706e2580000

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

[Edward Adam Davis]

syzbot reported btree node oob in bch2_btree_node_read_done. [1]

Add sanity check for written, avoid exceeding the allowed access limits
for btree node.

[1]

BUG: KASAN: slab-out-of-bounds in bch2_btree_node_read_done+0x950/0x5550 fs/bcachefs/btree_io.c:1128

Call Trace:

bch2_btree_node_read_done+0x950/0x5550 fs/bcachefs/btree_io.c:1128
btree_node_read_work+0x40e/0xe60 fs/bcachefs/btree_io.c:1440

bch2_btree_root_read+0x5f0/0x760 fs/bcachefs/btree_io.c:1928
read_btree_roots+0x2c6/0x840 fs/bcachefs/recovery.c:615
bch2_fs_recovery+0x261f/0x3a50 fs/bcachefs/recovery.c:1006
bch2_fs_start+0xaaf/0xda0 fs/bcachefs/super.c:1213
bch2_fs_get_tree+0xb39/0x1520 fs/bcachefs/fs.c:2488
vfs_get_tree+0x8f/0x2b0 fs/super.c:1815
do_new_mount+0x2a2/0x9e0 fs/namespace.c:3808

Reported-by: syzbot+ba7115...@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=ba71155d3eacc8f42477
Tested-by: syzbot+ba7115...@syzkaller.appspotmail.com
Signed-off-by: Edward Adam Davis <ead...@qq.com>
---
fs/bcachefs/btree_io.c | 7 +++++++
1 file changed, 7 insertions(+)

--
2.43.0