Re: KASAN: slab-use-after-free Read in cgroup_rstat_flush

From: Michal Koutný
Date: Mon Apr 14 2025 - 13:40:47 EST

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Hello.

On Mon, Apr 07, 2025 at 07:59:58AM -0400, ffhgfv <xnxc22xnxc22@xxxxxx> wrote:
> Hello, I found a bug titled " KASAN: slab-use-after-free Read in cgroup_rstat_flush " with modified syzkaller in the Linux6.14.
> If you fix this issue, please add the following tag to the commit: Reported-by: Jianzhou Zhao <xnxc22xnxc22@xxxxxx>, xingwei lee <xrivendell7@xxxxxxxxx>,Penglei Jiang <superman.xpt@xxxxxxxxx>
> I use the same kernel as syzbot instance upstream: f6e0150b2003fb2b9265028a618aa1732b3edc8f
> kernel config: https://syzkaller.appspot.com/text?tag=KernelConfig&x=da4b04ae798b7ef6
> compiler: gcc version 11.4.0
>
> Unfortunately, we do not have a repro.

Thanks for sharing the report.

> ------------[ cut here ]-----------------------------------------
> TITLE: KASAN: slab-use-after-free Read in cgroup_rstat_flush
> ==================================================================
> bridge_slave_0: left allmulticast mode
> bridge_slave_0: left promiscuous mode
> bridge0: port 1(bridge_slave_0) entered disabled state
> ==================================================================
> BUG: KASAN: slab-use-after-free in cgroup_rstat_cpu kernel/cgroup/rstat.c:19 [inline]
> BUG: KASAN: slab-use-after-free in cgroup_base_stat_flush kernel/cgroup/rstat.c:422 [inline]
> BUG: KASAN: slab-use-after-free in cgroup_rstat_flush+0x16ce/0x2180 kernel/cgroup/rstat.c:328

I read this like the struct cgroup is gone when the code try flushing
its respective stats (its ->rstat_cpu more precisely).

Namely,
__mem_cgroup_flush_stats
cgroup_rstat_flush(memcg->css.cgroup);
this reference is taken at cgroup creation in init_and_link_css()
and released only in css_free_rwork_fn().

> Read of size 8 at addr ffff888044f1a580 by task kworker/u8:3/10725
>
> CPU: 0 UID: 0 PID: 10725 Comm: kworker/u8:3 Not tainted 6.14.0-03565-gf6e0150b2003-dirty #3 PREEMPT(full)
> Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1 04/01/2014
> Workqueue: netns cleanup_net
> Call Trace:
> <task>
> __dump_stack lib/dump_stack.c:94 [inline]
> dump_stack_lvl+0x116/0x1b0 lib/dump_stack.c:120
> print_address_description mm/kasan/report.c:408 [inline]
> print_report+0xc1/0x630 mm/kasan/report.c:521
> kasan_report+0xca/0x100 mm/kasan/report.c:634
> cgroup_rstat_cpu kernel/cgroup/rstat.c:19 [inline]
> cgroup_base_stat_flush kernel/cgroup/rstat.c:422 [inline]
> cgroup_rstat_flush+0x16ce/0x2180 kernel/cgroup/rstat.c:328
> zswap_shrinker_count+0x280/0x570 mm/zswap.c:1272
> do_shrink_slab+0x80/0x1170 mm/shrinker.c:384
> shrink_slab+0x33d/0x12c0 mm/shrinker.c:664
> shrink_one+0x4a8/0x7c0 mm/vmscan.c:4868
> shrink_many mm/vmscan.c:4929 [inline]

I'm looking at this:

rcu_read_lock();

hlist_nulls_for_each_entry_rcu(lrugen, pos, &pgdat->memcg_lru.fifo[gen][bin], list) {
...

mem_cgroup_put(memcg);
memcg = NULL;

if (gen != READ_ONCE(lrugen->gen))
continue;

lruvec = container_of(lrugen, struct lruvec, lrugen);
memcg = lruvec_memcg(lruvec);

if (!mem_cgroup_tryget(memcg)) {
lru_gen_release_memcg(memcg);
memcg = NULL;
continue;
}

rcu_read_unlock();

op = shrink_one(lruvec, sc);

where shrink_one() may get a dead reference to memcg (where
shrink_slab_memcg() bails out when it's not online) but it's still _a_
reference, so css_free_rwork_fn() should not be executed yet.
And despite some indirections, the references of a chosen memcg seem
well-paired in shrink_many to me.

Then, I'm not so familiar with MGLRU to be able to tell whether
lrugens/memcgs are always properly referenced when stored into
pgdat->memcg_lru.fifo[gen][bin] (I Cc linux-mm). That'd be where I'd
look next...

> lru_gen_shrink_node mm/vmscan.c:5007 [inline]
> shrink_node+0x2687/0x3dc0 mm/vmscan.c:5978
> shrink_zones mm/vmscan.c:6237 [inline]
> do_try_to_free_pages+0x377/0x19b0 mm/vmscan.c:6299
> try_to_free_pages+0x2a1/0x690 mm/vmscan.c:6549
> __perform_reclaim mm/page_alloc.c:3929 [inline]
> __alloc_pages_direct_reclaim mm/page_alloc.c:3951 [inline]
> __alloc_pages_slowpath mm/page_alloc.c:4383 [inline]
> __alloc_frozen_pages_noprof+0xaca/0x2200 mm/page_alloc.c:4753
> alloc_pages_mpol+0x1f1/0x540 mm/mempolicy.c:2301
> alloc_slab_page mm/slub.c:2446 [inline]
> allocate_slab mm/slub.c:2610 [inline]
> new_slab+0x242/0x340 mm/slub.c:2663
> ___slab_alloc+0xb5f/0x1730 mm/slub.c:3849
> __slab_alloc.constprop.0+0x56/0xb0 mm/slub.c:3939
> __slab_alloc_node mm/slub.c:4014 [inline]
> slab_alloc_node mm/slub.c:4175 [inline]
> __kmalloc_cache_noprof+0x272/0x3f0 mm/slub.c:4344
> kmalloc_noprof include/linux/slab.h:902 [inline]
> netdevice_queue_work drivers/infiniband/core/roce_gid_mgmt.c:664 [inline]
> netdevice_event+0x36b/0x9e0 drivers/infiniband/core/roce_gid_mgmt.c:823
> notifier_call_chain+0xb9/0x420 kernel/notifier.c:85
> call_netdevice_notifiers_info+0xbe/0x140 net/core/dev.c:2206
> __netdev_upper_dev_unlink+0x14c/0x430 net/core/dev.c:8459
> netdev_upper_dev_unlink+0x7f/0xb0 net/core/dev.c:8486
> del_nbp+0x70d/0xd20 net/bridge/br_if.c:363
> br_dev_delete+0x99/0x1a0 net/bridge/br_if.c:386
> br_net_exit_batch_rtnl+0x116/0x1f0 net/bridge/br.c:376
> cleanup_net+0x551/0xb80 net/core/net_namespace.c:645
> process_one_work+0x9f9/0x1bd0 kernel/workqueue.c:3245
> process_scheduled_works kernel/workqueue.c:3329 [inline]
> worker_thread+0x674/0xe70 kernel/workqueue.c:3410
> kthread+0x3af/0x760 kernel/kthread.c:464
> ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:153
> ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
> </task>
>
> Allocated by task 1:
> kasan_save_stack+0x24/0x50 mm/kasan/common.c:47
> kasan_save_track+0x14/0x30 mm/kasan/common.c:68
> poison_kmalloc_redzone mm/kasan/common.c:377 [inline]
> __kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:394
> kasan_kmalloc include/linux/kasan.h:260 [inline]
> __do_kmalloc_node mm/slub.c:4318 [inline]
> __kmalloc_noprof+0x219/0x540 mm/slub.c:4330
> kmalloc_noprof include/linux/slab.h:906 [inline]
> kzalloc_noprof include/linux/slab.h:1036 [inline]
> cgroup_create kernel/cgroup/cgroup.c:5677 [inline]
> cgroup_mkdir+0x254/0x10d0 kernel/cgroup/cgroup.c:5827
> kernfs_iop_mkdir+0x15a/0x1f0 fs/kernfs/dir.c:1247
> vfs_mkdir+0x593/0x8d0 fs/namei.c:4324
> do_mkdirat+0x2dc/0x3d0 fs/namei.c:4357
> __do_sys_mkdir fs/namei.c:4379 [inline]
> __se_sys_mkdir fs/namei.c:4377 [inline]
> __x64_sys_mkdir+0xf3/0x140 fs/namei.c:4377
> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> do_syscall_64+0xcb/0x250 arch/x86/entry/syscall_64.c:94
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> Freed by task 12064:
> kasan_save_stack+0x24/0x50 mm/kasan/common.c:47
> kasan_save_track+0x14/0x30 mm/kasan/common.c:68
> kasan_save_free_info+0x3b/0x60 mm/kasan/generic.c:576
> poison_slab_object mm/kasan/common.c:247 [inline]
> __kasan_slab_free+0x54/0x70 mm/kasan/common.c:264
> kasan_slab_free include/linux/kasan.h:233 [inline]
> slab_free_hook mm/slub.c:2376 [inline]
> slab_free mm/slub.c:4633 [inline]
> kfree+0x148/0x4d0 mm/slub.c:4832
> css_free_rwork_fn+0x58f/0x1250 kernel/cgroup/cgroup.c:5435
> process_one_work+0x9f9/0x1bd0 kernel/workqueue.c:3245
> process_scheduled_works kernel/workqueue.c:3329 [inline]
> worker_thread+0x674/0xe70 kernel/workqueue.c:3410
> kthread+0x3af/0x760 kernel/kthread.c:464
> ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:153
> ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
>
> Last potentially related work creation:
> kasan_save_stack+0x24/0x50 mm/kasan/common.c:47
> kasan_record_aux_stack+0xb8/0xd0 mm/kasan/generic.c:548
> insert_work+0x36/0x230 kernel/workqueue.c:2183
> __queue_work+0x9d1/0x1110 kernel/workqueue.c:2344
> rcu_work_rcufn+0x5c/0x90 kernel/workqueue.c:2613
> rcu_do_batch kernel/rcu/tree.c:2568 [inline]
> rcu_core+0x79e/0x14f0 kernel/rcu/tree.c:2824
> handle_softirqs+0x1d1/0x870 kernel/softirq.c:561
> __do_softirq kernel/softirq.c:595 [inline]
> invoke_softirq kernel/softirq.c:435 [inline]
> __irq_exit_rcu+0x109/0x170 kernel/softirq.c:662
> irq_exit_rcu+0x9/0x30 kernel/softirq.c:678
> instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1049 [inline]
> sysvec_apic_timer_interrupt+0xa8/0xc0 arch/x86/kernel/apic/apic.c:1049
> asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702
>
> Second to last potentially related work creation:
> kasan_save_stack+0x24/0x50 mm/kasan/common.c:47
> kasan_record_aux_stack+0xb8/0xd0 mm/kasan/generic.c:548
> __call_rcu_common.constprop.0+0x99/0x9e0 kernel/rcu/tree.c:3082
> call_rcu_hurry include/linux/rcupdate.h:115 [inline]
> queue_rcu_work+0xa9/0xe0 kernel/workqueue.c:2638
> process_one_work+0x9f9/0x1bd0 kernel/workqueue.c:3245
> process_scheduled_works kernel/workqueue.c:3329 [inline]
> worker_thread+0x674/0xe70 kernel/workqueue.c:3410
> kthread+0x3af/0x760 kernel/kthread.c:464
> ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:153
> ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
>
> The buggy address belongs to the object at ffff888044f1a000
> which belongs to the cache kmalloc-4k of size 4096
> The buggy address is located 1408 bytes inside of
> freed 4096-byte region [ffff888044f1a000, ffff888044f1b000)
>
> The buggy address belongs to the physical page:
> page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x44f18
> head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
> anon flags: 0x4fff00000000040(head|node=1|zone=1|lastcpupid=0x7ff)
> page_type: f5(slab)
> raw: 04fff00000000040 ffff88801b042140 0000000000000000 dead000000000001
> raw: 0000000000000000 0000000000040004 00000000f5000000 0000000000000000
> head: 04fff00000000040 ffff88801b042140 0000000000000000 dead000000000001
> head: 0000000000000000 0000000000040004 00000000f5000000 0000000000000000
> head: 04fff00000000003 ffffea000113c601 ffffffffffffffff 0000000000000000
> head: 0000000000000008 0000000000000000 00000000ffffffff 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 0xd2040(__GFP_IO|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 1, tgid 1 (systemd), ts 113702677351, free_ts 113428419852
> set_page_owner include/linux/page_owner.h:32 [inline]
> post_alloc_hook+0x193/0x1c0 mm/page_alloc.c:1551
> prep_new_page mm/page_alloc.c:1559 [inline]
> get_page_from_freelist+0xe41/0x2b40 mm/page_alloc.c:3477
> __alloc_frozen_pages_noprof+0x21b/0x2200 mm/page_alloc.c:4740
> alloc_pages_mpol+0x1f1/0x540 mm/mempolicy.c:2301
> alloc_slab_page mm/slub.c:2446 [inline]
> allocate_slab mm/slub.c:2610 [inline]
> new_slab+0x242/0x340 mm/slub.c:2663
> ___slab_alloc+0xb5f/0x1730 mm/slub.c:3849
> __slab_alloc.constprop.0+0x56/0xb0 mm/slub.c:3939
> __slab_alloc_node mm/slub.c:4014 [inline]
> slab_alloc_node mm/slub.c:4175 [inline]
> __do_kmalloc_node mm/slub.c:4317 [inline]
> __kmalloc_noprof+0x2b2/0x540 mm/slub.c:4330
> kmalloc_noprof include/linux/slab.h:906 [inline]
> tomoyo_realpath_from_path+0xc3/0x600 security/tomoyo/realpath.c:251
> tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
> tomoyo_check_open_permission+0x298/0x3a0 security/tomoyo/file.c:771
> tomoyo_file_open+0x69/0x90 security/tomoyo/tomoyo.c:334
> security_file_open+0x88/0x200 security/security.c:3114
> do_dentry_open+0x575/0x1c20 fs/open.c:933
> vfs_open+0x82/0x3f0 fs/open.c:1086
> do_open fs/namei.c:3845 [inline]
> path_openat+0x1d53/0x2960 fs/namei.c:4004
> do_filp_open+0x1f7/0x460 fs/namei.c:4031
> page last free pid 1 tgid 1 stack trace:
> reset_page_owner include/linux/page_owner.h:25 [inline]
> free_pages_prepare mm/page_alloc.c:1127 [inline]
> free_frozen_pages+0x719/0xfe0 mm/page_alloc.c:2660
> discard_slab mm/slub.c:2707 [inline]
> __put_partials+0x176/0x1d0 mm/slub.c:3176
> qlink_free mm/kasan/quarantine.c:163 [inline]
> qlist_free_all+0x50/0x120 mm/kasan/quarantine.c:179
> kasan_quarantine_reduce+0x195/0x1e0 mm/kasan/quarantine.c:286
> __kasan_slab_alloc+0x67/0x90 mm/kasan/common.c:329
> kasan_slab_alloc include/linux/kasan.h:250 [inline]
> slab_post_alloc_hook mm/slub.c:4138 [inline]
> slab_alloc_node mm/slub.c:4187 [inline]
> kmem_cache_alloc_noprof+0x160/0x3e0 mm/slub.c:4194
> getname_flags.part.0+0x48/0x540 fs/namei.c:146
> getname_flags+0x95/0xe0 include/linux/audit.h:322
> user_path_at+0x27/0x90 fs/namei.c:3084
> __do_sys_chdir fs/open.c:557 [inline]
> __se_sys_chdir fs/open.c:551 [inline]
> __x64_sys_chdir+0xb6/0x260 fs/open.c:551
> do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
> do_syscall_64+0xcb/0x250 arch/x86/entry/syscall_64.c:94
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
>
> Memory state around the buggy address:
> ffff888044f1a480: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff888044f1a500: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> >ffff888044f1a580: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ^
> ffff888044f1a600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ffff888044f1a680: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
> ==================================================================
>
>
> I hope it helps.
> Best regards
> Jianzhou Zhao</superman.xpt@xxxxxxxxx></xrivendell7@xxxxxxxxx></xnxc22xnxc22@xxxxxx>

Michal

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