Re: [syzbot] [cgroups?] KASAN: slab-use-after-free Read in pressure_write

[syzbot <syzbot+33e571025d88efd1312c@syzkaller.appspotmail.com>]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
KASAN: slab-use-after-free Read in pressure_write

==================================================================
BUG: KASAN: slab-use-after-free in pressure_write+0xa4/0x210 kernel/cgroup/cgroup.c:4011
Read of size 8 at addr ffff888027b54308 by task syz.4.2181/12429

CPU: 1 UID: 0 PID: 12429 Comm: syz.4.2181 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xba/0x230 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 pressure_write+0xa4/0x210 kernel/cgroup/cgroup.c:4011
 cgroup_file_write+0x36f/0x790 kernel/cgroup/cgroup.c:4311
 kernfs_fop_write_iter+0x3b0/0x540 fs/kernfs/file.c:352
 new_sync_write fs/read_write.c:595 [inline]
 vfs_write+0x629/0xba0 fs/read_write.c:688
 ksys_write+0x156/0x270 fs/read_write.c:740
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f4480b7c819
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:00007f44801de028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f4480df5fa0 RCX: 00007f4480b7c819
RDX: 000000000000002f RSI: 0000200000000080 RDI: 0000000000000004
RBP: 00007f4480c12c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f4480df6038 R14: 00007f4480df5fa0 R15: 00007ffc6ce72378
 </TASK>

Allocated by task 12429:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __kmalloc_cache_noprof+0x3a6/0x690 mm/slub.c:5380
 kmalloc_noprof include/linux/slab.h:950 [inline]
 kzalloc_noprof include/linux/slab.h:1188 [inline]
 cgroup_file_open+0x90/0x3a0 kernel/cgroup/cgroup.c:4256
 kernfs_fop_open+0x9eb/0xcb0 fs/kernfs/file.c:724
 do_dentry_open+0x83d/0x13e0 fs/open.c:949
 vfs_open+0x3b/0x350 fs/open.c:1081
 do_open fs/namei.c:4677 [inline]
 path_openat+0x2e43/0x38a0 fs/namei.c:4836
 do_file_open+0x23e/0x4a0 fs/namei.c:4865
 do_sys_openat2+0x113/0x200 fs/open.c:1366
 do_sys_open fs/open.c:1372 [inline]
 __do_sys_openat fs/open.c:1388 [inline]
 __se_sys_openat fs/open.c:1383 [inline]
 __x64_sys_openat+0x138/0x170 fs/open.c:1383
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 12430:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2685 [inline]
 slab_free mm/slub.c:6165 [inline]
 kfree+0x1c1/0x6c0 mm/slub.c:6483
 cgroup_file_release+0xd6/0x100 kernel/cgroup/cgroup.c:4283
 kernfs_release_file fs/kernfs/file.c:764 [inline]
 kernfs_drain_open_files+0x392/0x720 fs/kernfs/file.c:836
 kernfs_drain+0x470/0x600 fs/kernfs/dir.c:525
 __kernfs_remove+0x3cf/0x660 fs/kernfs/dir.c:1513
 kernfs_remove_by_name_ns+0xaf/0x130 fs/kernfs/dir.c:1722
 kernfs_remove_by_name include/linux/kernfs.h:633 [inline]
 cgroup_rm_file kernel/cgroup/cgroup.c:1758 [inline]
 cgroup_addrm_files+0x684/0xc30 kernel/cgroup/cgroup.c:4483
 cgroup_destroy_locked+0x321/0x630 kernel/cgroup/cgroup.c:6197
 cgroup_rmdir+0x3e8/0x710 kernel/cgroup/cgroup.c:6311
 kernfs_iop_rmdir+0x203/0x350 fs/kernfs/dir.c:1291
 vfs_rmdir+0x400/0x6f0 fs/namei.c:5344
 filename_rmdir+0x292/0x520 fs/namei.c:5399
 __do_sys_rmdir fs/namei.c:5422 [inline]
 __se_sys_rmdir+0x2e/0x140 fs/namei.c:5419
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x14d/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff888027b54300
 which belongs to the cache kmalloc-192 of size 192
The buggy address is located 8 bytes inside of
 freed 192-byte region [ffff888027b54300, ffff888027b543c0)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x27b54
flags: 0x80000000000000(node=0|zone=1)
page_type: f5(slab)
raw: 0080000000000000 ffff88813fe1a3c0 dead000000000100 dead000000000122
raw: 0000000000000000 0000000800100010 00000000f5000000 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 0xd2cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 1, tgid 1 (swapper/0), ts 8324059558, free_ts 8317685157
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x231/0x280 mm/page_alloc.c:1889
 prep_new_page mm/page_alloc.c:1897 [inline]
 get_page_from_freelist+0x28bb/0x2950 mm/page_alloc.c:3962
 __alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5250
 alloc_slab_page mm/slub.c:3292 [inline]
 allocate_slab+0x77/0x660 mm/slub.c:3481
 new_slab mm/slub.c:3539 [inline]
 refill_objects+0x334/0x3c0 mm/slub.c:7175
 refill_sheaf mm/slub.c:2812 [inline]
 __pcs_replace_empty_main+0x35c/0x710 mm/slub.c:4615
 alloc_from_pcs mm/slub.c:4717 [inline]
 slab_alloc_node mm/slub.c:4851 [inline]
 __do_kmalloc_node mm/slub.c:5259 [inline]
 __kmalloc_noprof+0x530/0x7b0 mm/slub.c:5272
 kmalloc_noprof include/linux/slab.h:954 [inline]
 kzalloc_noprof include/linux/slab.h:1188 [inline]
 new_dir fs/proc/proc_sysctl.c:966 [inline]
 get_subdir fs/proc/proc_sysctl.c:1010 [inline]
 sysctl_mkdir_p fs/proc/proc_sysctl.c:1320 [inline]
 __register_sysctl_table+0xba1/0x1340 fs/proc/proc_sysctl.c:1395
 __devinet_sysctl_register+0x386/0x490 net/ipv4/devinet.c:2677
 devinet_sysctl_register+0x187/0x200 net/ipv4/devinet.c:2717
 inetdev_init+0x2a4/0x4e0 net/ipv4/devinet.c:291
 inetdev_event+0x30d/0x1610 net/ipv4/devinet.c:1590
 notifier_call_chain+0x1be/0x400 kernel/notifier.c:85
 call_netdevice_notifiers_extack net/core/dev.c:2287 [inline]
 call_netdevice_notifiers net/core/dev.c:2301 [inline]
 register_netdevice+0x1751/0x1d10 net/core/dev.c:11479
 dummy_init_one+0x69/0x90 drivers/net/dummy.c:159
 dummy_init_module+0x3a/0xa0 drivers/net/dummy.c:180
page last free pid 43 tgid 43 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 __free_pages_prepare mm/page_alloc.c:1433 [inline]
 __free_frozen_pages+0xfe3/0x1170 mm/page_alloc.c:2978
 vfree+0x2ac/0x470 mm/vmalloc.c:3479
 delayed_vfree_work+0x55/0x80 mm/vmalloc.c:3398
 process_one_work kernel/workqueue.c:3276 [inline]
 process_scheduled_works+0xb6e/0x18c0 kernel/workqueue.c:3359
 worker_thread+0xa53/0xfc0 kernel/workqueue.c:3440
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

Memory state around the buggy address:
 ffff888027b54200: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
 ffff888027b54280: 00 00 fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888027b54300: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                      ^
 ffff888027b54380: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
 ffff888027b54400: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================


Tested on:

commit:         9a9c8ce3 Merge tag 'kbuild-fixes-7.0-4' of git://git.k..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1663574e580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=45cb3c58fd963c27
dashboard link: https://syzkaller.appspot.com/bug?extid=33e571025d88efd1312c
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
patch:          https://syzkaller.appspot.com/x/patch.diff?x=1483574e580000