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KASAN: use-after-free Read in exact_lock (3)

Status: premoderation: reported on 2026/06/06 04:43
Reported-by: syzbot+5ed10e5bda573205a250@syzkaller.appspotmail.com
First crash: 38d, last: 3d16h
▶ ▼ Similar bugs (4)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
android-54 KASAN: use-after-free Read in exact_lock 19 1 1298d 1298d 0/2 auto-obsoleted due to no activity on 2023/04/22 15:12
android-54 KASAN: use-after-free Read in exact_lock (2) 19 14 426d 499d 0/2 auto-obsoleted due to no activity on 2025/07/29 08:03
android-5-10 KASAN: use-after-free Read in exact_lock (2) 19 172 365d 444d 0/2 auto-obsoleted due to no activity on 2025/09/02 09:54
android-5-10 KASAN: use-after-free Read in exact_lock 19 53 496d 505d 0/2 auto-obsoleted due to no activity on 2025/04/24 06:37

Sample crash report:
==================================================================
BUG: KASAN: use-after-free in get_disk_and_module block/genhd.c:1787 [inline]
BUG: KASAN: use-after-free in exact_lock+0x38/0xc0 block/genhd.c:677
Read of size 8 at addr ffff88810954c460 by task syz.0.3242/11769

CPU: 1 PID: 11769 Comm: syz.0.3242 Tainted: G        W         syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
Call Trace:
 __dump_stack+0x21/0x24 lib/dump_stack.c:77
 dump_stack_lvl+0x1a7/0x208 lib/dump_stack.c:118
 print_address_description+0x7f/0x2c0 mm/kasan/report.c:248
 __kasan_report mm/kasan/report.c:435 [inline]
 kasan_report+0x100/0x140 mm/kasan/report.c:452
 __asan_report_load8_noabort+0x14/0x20 mm/kasan/report_generic.c:309
 get_disk_and_module block/genhd.c:1787 [inline]
 exact_lock+0x38/0xc0 block/genhd.c:677
 kobj_lookup+0x284/0x420 drivers/base/map.c:119
 get_gendisk+0xe2/0x350 block/genhd.c:1001
 bdev_get_gendisk fs/block_dev.c:1110 [inline]
 __blkdev_get+0xc6/0x13c0 fs/block_dev.c:1474
 blkdev_get fs/block_dev.c:1653 [inline]
 blkdev_open+0x23b/0x490 fs/block_dev.c:1770
 do_dentry_open+0x7a5/0x10a0 fs/open.c:819
 vfs_open+0x73/0x80 fs/open.c:944
 do_open fs/namei.c:3399 [inline]
 path_openat+0x26c3/0x3040 fs/namei.c:3517
 do_filp_open+0x1df/0x400 fs/namei.c:3544
 do_sys_openat2+0x19f/0x750 fs/open.c:1219
 do_sys_open fs/open.c:1235 [inline]
 __do_sys_creat fs/open.c:1311 [inline]
 __se_sys_creat fs/open.c:1305 [inline]
 __x64_sys_creat+0x8e/0xb0 fs/open.c:1305
 do_syscall_64+0x31/0x40 arch/x86/entry/common.c:46
 entry_SYSCALL_64_after_hwframe+0x61/0xcb
RIP: 0033:0x7ff426a42e59
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ff42545a028 EFLAGS: 00000246 ORIG_RAX: 0000000000000055
RAX: ffffffffffffffda RBX: 00007ff426ccb180 RCX: 00007ff426a42e59
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 00002000000000c0
RBP: 00007ff426ad8e6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007ff426ccb218 R14: 00007ff426ccb180 R15: 00007ffc8ad4a578

Allocated by task 1:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track mm/kasan/common.c:45 [inline]
 set_alloc_info mm/kasan/common.c:430 [inline]
 ____kasan_kmalloc mm/kasan/common.c:509 [inline]
 __kasan_kmalloc+0xd4/0x100 mm/kasan/common.c:518
 kasan_kmalloc include/linux/kasan.h:254 [inline]
 kmem_cache_alloc_trace+0x179/0x2e0 mm/slub.c:2979
 kmem_cache_alloc_node_trace include/linux/slab.h:443 [inline]
 kmalloc_node include/linux/slab.h:573 [inline]
 kzalloc_node include/linux/slab.h:678 [inline]
 __alloc_disk_node+0x79/0x5b0 block/genhd.c:1727
 loop_add+0x33a/0x770 drivers/block/loop.c:2158
 loop_init+0x1bf/0x1ff drivers/block/loop.c:2403
 do_one_initcall+0x205/0x5e0 init/main.c:1211
 do_initcall_level+0x174/0x2dc init/main.c:1284
 do_initcalls+0x50/0x92 init/main.c:1300
 do_basic_setup+0x88/0x8f init/main.c:1320
 kernel_init_freeable+0x28c/0x3c3 init/main.c:1524
 kernel_init+0x11/0x1a0 init/main.c:1411
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:298

Freed by task 24:
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track+0x4a/0x70 mm/kasan/common.c:45
 kasan_set_free_info+0x23/0x40 mm/kasan/generic.c:370
 ____kasan_slab_free+0x125/0x160 mm/kasan/common.c:362
 __kasan_slab_free+0x11/0x20 mm/kasan/common.c:370
 kasan_slab_free include/linux/kasan.h:220 [inline]
 slab_free_hook mm/slub.c:1600 [inline]
 slab_free_freelist_hook+0xc5/0x190 mm/slub.c:1626
 slab_free mm/slub.c:3208 [inline]
 kfree+0xc0/0x270 mm/slub.c:4196
 skb_free_head net/core/skbuff.c:606 [inline]
 skb_release_data+0x53b/0x690 net/core/skbuff.c:626
 skb_release_all net/core/skbuff.c:680 [inline]
 __kfree_skb net/core/skbuff.c:694 [inline]
 kfree_skb+0xb9/0x2f0 net/core/skbuff.c:713
 kauditd_hold_skb+0x116/0x210 kernel/audit.c:614
 kauditd_send_queue+0x28c/0x2e0 kernel/audit.c:769
 kauditd_thread+0x4e4/0x870 kernel/audit.c:893
 kthread+0x324/0x3b0 kernel/kthread.c:313
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:298

The buggy address belongs to the object at ffff88810954c000
 which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 1120 bytes inside of
 2048-byte region [ffff88810954c000, ffff88810954c800)
The buggy address belongs to the page:
page:ffffea0004255200 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x109548
head:ffffea0004255200 order:3 compound_mapcount:0 compound_pincount:0
flags: 0x4000000000010200(slab|head)
raw: 4000000000010200 ffffea0004afc400 0000000200000002 ffff888100042d80
raw: 0000000000000000 0000000000080008 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 1, ts 2128712262, free_ts 0
 set_page_owner include/linux/page_owner.h:35 [inline]
 post_alloc_hook mm/page_alloc.c:2456 [inline]
 prep_new_page+0x176/0x190 mm/page_alloc.c:2462
 get_page_from_freelist+0x225f/0x23f0 mm/page_alloc.c:4254
 __alloc_pages_nodemask+0x29a/0x640 mm/page_alloc.c:5384
 alloc_slab_page mm/slub.c:-1 [inline]
 allocate_slab mm/slub.c:1813 [inline]
 new_slab+0x84/0x3f0 mm/slub.c:1874
 new_slab_objects mm/slub.c:2632 [inline]
 ___slab_alloc+0x2f8/0x4c0 mm/slub.c:2796
 __slab_alloc+0x63/0xa0 mm/slub.c:2836
 slab_alloc_node mm/slub.c:2918 [inline]
 slab_alloc mm/slub.c:2960 [inline]
 kmem_cache_alloc_trace+0x1a8/0x2e0 mm/slub.c:2977
 kmem_cache_alloc_node_trace include/linux/slab.h:443 [inline]
 kmalloc_node include/linux/slab.h:573 [inline]
 kzalloc_node include/linux/slab.h:678 [inline]
 bdi_alloc+0x4e/0x110 mm/backing-dev.c:747
 blk_alloc_queue+0xf8/0x5f0 block/blk-core.c:535
 brd_alloc+0xfa/0x3e0 drivers/block/brd.c:383
 brd_init+0x125/0x468 drivers/block/brd.c:517
 do_one_initcall+0x205/0x5e0 init/main.c:1211
 do_initcall_level+0x174/0x2dc init/main.c:1284
 do_initcalls+0x50/0x92 init/main.c:1300
 do_basic_setup+0x88/0x8f init/main.c:1320
 kernel_init_freeable+0x28c/0x3c3 init/main.c:1524
page_owner free stack trace missing

Memory state around the buggy address:
 ffff88810954c300: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88810954c380: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
>ffff88810954c400: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                       ^
 ffff88810954c480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff88810954c500: 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
2026/07/10 18:23 android13-5.10-lts 50b3a256e550 99e64375 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in exact_lock
2026/06/06 04:42 android13-5.10-lts 4a079a5d30eb cc095639 .config console log report info [disk image] [vmlinux] [kernel image] ci2-android-5-10 KASAN: use-after-free Read in exact_lock
* Struck through repros no longer work on HEAD.