KASAN: slab-out-of-bounds Read in drop_buffers (2)

Status: fixed on 2026/04/11 13:11
Bug presence: origin:lts-only
[Documentation on labels]
Reported-by: syzbot+5b886a2e03529dbcef81@syzkaller.appspotmail.com
Fix commit: 4a977fcc0d6a erofs: Fix the slab-out-of-bounds in drop_buffers()
First crash: 309d, last: 108d
Fix bisection: the issue occurs on the latest tested release (bisect log)
Crash: KASAN: slab-out-of-bounds Read in drop_buffers (log)
Repro: C syz .config
  
▶ ▼ Discussions (2)
Title Replies (including bot) Last reply
[PATCH v2 6.1] erofs: Fix the slab-out-of-bounds in drop_buffers() 2 (2) 2026/03/24 02:24
[PATCH 6.1] erofs: Fix the slab-out-of-bounds in drop_buffers() 2 (2) 2026/03/23 08:58
▶ ▼ Bug presence (2)
Date Name Commit Repro Result
2025/09/24 linux-6.1.y (ToT) 363a599da6d9 C [report] KASAN: slab-out-of-bounds Read in drop_buffers
2025/09/24 upstream (ToT) cec1e6e5d1ab C Didn't crash
▶ ▼ Similar bugs (7)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.1 KASAN: slab-out-of-bounds Read in drop_buffers 17 1 540d 540d 0/3 auto-obsoleted due to no activity on 2025/05/11 23:03
upstream KASAN: null-ptr-deref Read in drop_buffers (5) prio:high fs 11 14 41d 257d 0/29 upstream: reported on 2025/11/10 12:38
upstream KASAN: null-ptr-deref Read in drop_buffers (2) jfs 11 C error 252 878d 1089d 0/29 auto-obsoleted due to no activity on 2024/05/08 22:28
upstream KASAN: null-ptr-deref Read in drop_buffers kernfs 11 5 1365d 1365d 0/29 auto-obsoleted due to no activity on 2023/02/27 02:04
upstream KASAN: null-ptr-deref Read in drop_buffers (4) fs 17 228 333d 342d 0/29 auto-obsoleted due to no activity on 2025/10/15 13:15
linux-6.1 KASAN: null-ptr-deref Read in drop_buffers 11 1 52d 52d 0/3 upstream: reported on 2026/06/03 12:36
upstream KASAN: null-ptr-deref Read in drop_buffers (3) fs 17 C 98 496d 662d 0/29 auto-obsoleted due to no activity on 2025/06/08 23:43
▶ ▼ Fix bisection attempts (2)
Created Duration User Patch Repo Result
2026/01/16 19:28 3h40m (2) fix candidate upstream OK (0) job log
2025/11/04 01:44 1h50m bisect fix linux-6.1.y OK (0) job log log

Sample crash report:
==================================================================
BUG: KASAN: slab-out-of-bounds in instrument_atomic_read include/linux/instrumented.h:72 [inline]
BUG: KASAN: slab-out-of-bounds in atomic_read include/linux/atomic/atomic-instrumented.h:27 [inline]
BUG: KASAN: slab-out-of-bounds in buffer_busy fs/buffer.c:2784 [inline]
BUG: KASAN: slab-out-of-bounds in drop_buffers+0x65/0x6a0 fs/buffer.c:2796
Read of size 4 at addr ffff88807cb9e760 by task kswapd1/83

CPU: 1 PID: 83 Comm: kswapd1 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x168/0x22e lib/dump_stack.c:106
 print_address_description mm/kasan/report.c:316 [inline]
 print_report+0xa8/0x210 mm/kasan/report.c:420
 kasan_report+0x10b/0x140 mm/kasan/report.c:524
 check_region_inline mm/kasan/generic.c:-1 [inline]
 kasan_check_range+0x27b/0x290 mm/kasan/generic.c:189
 instrument_atomic_read include/linux/instrumented.h:72 [inline]
 atomic_read include/linux/atomic/atomic-instrumented.h:27 [inline]
 buffer_busy fs/buffer.c:2784 [inline]
 drop_buffers+0x65/0x6a0 fs/buffer.c:2796
 try_to_free_buffers+0x205/0x520 fs/buffer.c:2826
 shrink_folio_list+0x209e/0x7ae0 mm/vmscan.c:2003
 evict_folios+0xa76/0x2270 mm/vmscan.c:5046
 lru_gen_shrink_lruvec mm/vmscan.c:5229 [inline]
 shrink_lruvec+0xbdd/0x3c60 mm/vmscan.c:5924
 </TASK>

Allocated by task 4523:
 kasan_save_stack mm/kasan/common.c:45 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:52
 ____kasan_kmalloc mm/kasan/common.c:374 [inline]
 __kasan_kmalloc+0x8e/0xa0 mm/kasan/common.c:383
 kasan_kmalloc include/linux/kasan.h:211 [inline]
 __do_kmalloc_node mm/slab_common.c:936 [inline]
 __kmalloc+0xb0/0x240 mm/slab_common.c:949
 kmalloc include/linux/slab.h:568 [inline]
 kzalloc include/linux/slab.h:699 [inline]
 iomap_page_create+0x14a/0x600 fs/iomap/buffered-io.c:61
 iomap_readpage_iter+0x240/0x8f0 fs/iomap/buffered-io.c:273
 iomap_read_folio+0x2e7/0x7f0 fs/iomap/buffered-io.c:344
 filemap_read_folio+0x160/0x760 mm/filemap.c:2490
 do_read_cache_folio+0x2a0/0x760 mm/filemap.c:3659
 erofs_bread+0x18e/0x670 fs/erofs/data.c:50
 erofs_find_target_block fs/erofs/namei.c:102 [inline]
 erofs_namei+0x28f/0xf00 fs/erofs/namei.c:175
 erofs_lookup+0x14b/0x390 fs/erofs/namei.c:204
 lookup_one_qstr_excl+0x10e/0x240 fs/namei.c:1613
 filename_create+0x21e/0x450 fs/namei.c:3885
 do_mkdirat+0x9d/0x430 fs/namei.c:4129
 __do_sys_mkdirat fs/namei.c:4154 [inline]
 __se_sys_mkdirat fs/namei.c:4152 [inline]
 __x64_sys_mkdirat+0x85/0x90 fs/namei.c:4152
 do_syscall_x64 arch/x86/entry/common.c:51 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:81
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

The buggy address belongs to the object at ffff88807cb9e700
 which belongs to the cache kmalloc-96 of size 96
The buggy address is located 0 bytes to the right of
 96-byte region [ffff88807cb9e700, ffff88807cb9e760)

The buggy address belongs to the physical page:
page:ffffea0001f2e780 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x7cb9e
flags: 0xfff00000000200(slab|node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000200 0000000000000000 dead000000000001 ffff888017441780
raw: 0000000000000000 0000000080200020 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x112a20(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_HARDWALL), pid 14, tgid 14 (kworker/0:1), ts 83986767473, free_ts 82881977829
 set_page_owner include/linux/page_owner.h:31 [inline]
 post_alloc_hook+0x173/0x1a0 mm/page_alloc.c:2532
 prep_new_page mm/page_alloc.c:2539 [inline]
 get_page_from_freelist+0x1a26/0x1ac0 mm/page_alloc.c:4328
 __alloc_pages+0x1df/0x4e0 mm/page_alloc.c:5614
 __alloc_pages_node include/linux/gfp.h:237 [inline]
 alloc_slab_page+0x4f/0x160 mm/slub.c:1801
 allocate_slab mm/slub.c:1944 [inline]
 new_slab+0x87/0x2c0 mm/slub.c:1997
 ___slab_alloc+0xbc6/0x1230 mm/slub.c:3154
 __slab_alloc mm/slub.c:3240 [inline]
 slab_alloc_node mm/slub.c:3325 [inline]
 __kmem_cache_alloc_node+0x1a0/0x260 mm/slub.c:3398
 __do_kmalloc_node mm/slab_common.c:935 [inline]
 __kmalloc_node+0xa0/0x240 mm/slab_common.c:943
 kmalloc_array_node include/linux/slab.h:676 [inline]
 kcalloc_node include/linux/slab.h:681 [inline]
 memcg_alloc_slab_cgroups+0x83/0x120 mm/memcontrol.c:2889
 account_slab mm/slab.h:635 [inline]
 allocate_slab mm/slub.c:1962 [inline]
 new_slab+0xc3/0x2c0 mm/slub.c:1997
 ___slab_alloc+0xbc6/0x1230 mm/slub.c:3154
 __slab_alloc mm/slub.c:3240 [inline]
 slab_alloc_node mm/slub.c:3325 [inline]
 slab_alloc mm/slub.c:3367 [inline]
 __kmem_cache_alloc_lru mm/slub.c:3374 [inline]
 kmem_cache_alloc+0x1b7/0x2f0 mm/slub.c:3383
 dst_alloc+0x101/0x160 net/core/dst.c:88
 ip6_dst_alloc net/ipv6/route.c:345 [inline]
 icmp6_dst_alloc+0x7f/0x460 net/ipv6/route.c:3308
 mld_sendpack+0x710/0xe80 net/ipv6/mcast.c:1814
 mld_dad_work+0x3c/0x270 net/ipv6/mcast.c:2267
page last free stack trace:
 reset_page_owner include/linux/page_owner.h:24 [inline]
 free_pages_prepare mm/page_alloc.c:1459 [inline]
 free_pcp_prepare mm/page_alloc.c:1509 [inline]
 free_unref_page_prepare+0x8b4/0x9a0 mm/page_alloc.c:3384
 free_unref_page+0x2e/0x3f0 mm/page_alloc.c:3479
 __vunmap+0x856/0xa00 mm/vmalloc.c:2726
 kcov_put kernel/kcov.c:437 [inline]
 kcov_close+0x27/0x50 kernel/kcov.c:533
 __fput+0x22c/0x920 fs/file_table.c:320
 task_work_run+0x1ca/0x250 kernel/task_work.c:203
 exit_task_work include/linux/task_work.h:39 [inline]
 do_exit+0x93e/0x2400 kernel/exit.c:880
 do_group_exit+0x217/0x2d0 kernel/exit.c:1022
 get_signal+0x1272/0x1350 kernel/signal.c:2871
 arch_do_signal_or_restart+0xb7/0x1240 arch/x86/kernel/signal.c:871
 exit_to_user_mode_loop+0x70/0x110 kernel/entry/common.c:174
 exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:210
 __syscall_exit_to_user_mode_work kernel/entry/common.c:292 [inline]
 syscall_exit_to_user_mode+0x16/0x40 kernel/entry/common.c:303
 do_syscall_64+0x58/0xa0 arch/x86/entry/common.c:87
 entry_SYSCALL_64_after_hwframe+0x68/0xd2

Memory state around the buggy address:
 ffff88807cb9e600: 00 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc
 ffff88807cb9e680: 00 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc
>ffff88807cb9e700: 00 00 00 00 00 00 00 00 00 00 fc fc fc fc fc fc
                                                       ^
 ffff88807cb9e780: 00 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc
 ffff88807cb9e800: 00 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc
==================================================================

Crashes (18):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/01/04 06:02 linux-6.1.y 50cbba13faa2 d6526ea3 .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci2-linux-6-1-kasan KASAN: slab-out-of-bounds Read in drop_buffers
2025/09/20 18:35 linux-6.1.y 363a599da6d9 67c37560 .config console log report syz / log C [disk image] [vmlinux] [kernel image] [mounted in repro (corrupt fs)] ci2-linux-6-1-kasan KASAN: slab-out-of-bounds Read in drop_buffers
2026/03/22 10:40 linux-6.1.y f2ddafa93a25 5b92003d .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan KASAN: slab-out-of-bounds Read in drop_buffers
2026/03/12 06:20 linux-6.1.y f2ddafa93a25 2d88ab01 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan KASAN: slab-out-of-bounds Read in drop_buffers
2026/03/07 05:36 linux-6.1.y f2ddafa93a25 5cb44a80 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan KASAN: slab-out-of-bounds Read in drop_buffers
2026/03/02 19:40 linux-6.1.y 779f9571ac3e b9dd6534 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan KASAN: slab-out-of-bounds Read in drop_buffers
2026/03/02 19:40 linux-6.1.y 779f9571ac3e b9dd6534 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan KASAN: slab-out-of-bounds Read in drop_buffers
2026/03/02 19:40 linux-6.1.y 779f9571ac3e b9dd6534 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan KASAN: slab-out-of-bounds Read in drop_buffers
2026/02/27 21:28 linux-6.1.y 779f9571ac3e 2cf092b8 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan KASAN: slab-out-of-bounds Read in drop_buffers
2026/01/04 03:08 linux-6.1.y 50cbba13faa2 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan KASAN: slab-out-of-bounds Read in drop_buffers
2025/12/28 04:07 linux-6.1.y 50cbba13faa2 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan KASAN: slab-out-of-bounds Read in drop_buffers
2025/09/19 09:12 linux-6.1.y 3db754f56897 e2beed91 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan KASAN: slab-out-of-bounds Read in drop_buffers
2026/04/08 19:12 linux-6.1.y 1989cd3d56e2 d9b7f621 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-arm64 KASAN: slab-out-of-bounds Read in drop_buffers
2026/03/11 10:08 linux-6.1.y f2ddafa93a25 86914af9 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-arm64 KASAN: slab-out-of-bounds Read in drop_buffers
2026/01/29 00:57 linux-6.1.y cd9b81672742 0adc945e .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-arm64 KASAN: slab-out-of-bounds Read in drop_buffers
2025/12/27 10:31 linux-6.1.y 50cbba13faa2 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-arm64 KASAN: slab-out-of-bounds Read in drop_buffers
2025/12/09 03:30 linux-6.1.y 50cbba13faa2 d6526ea3 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-arm64 KASAN: slab-out-of-bounds Read in drop_buffers
2025/11/15 12:53 linux-6.1.y f6e38ae624cf f7988ea4 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-arm64 KASAN: slab-out-of-bounds Read in drop_buffers
* Struck through repros no longer work on HEAD.