[syzbot] [nfs?] KASAN: slab-use-after-free Read in add_to_unconfirmed

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    6addb4f38557 Merge tag 'edac_urgent_for_v7.3_rc6' of git:/..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=113b17f5580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=23e5acac5c98285f
dashboard link: https://syzkaller.appspot.com/bug?extid=9c7b9c5f6dd1d470b605
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/484fafd2304b/disk-6addb4f3.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/3a897e82997f/vmlinux-6addb4f3.xz
kernel image: https://storage.googleapis.com/syzbot-assets/57fc9f6de4c3/bzImage-6addb4f3.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+9c7b9c5f6dd1d470b605@xxxxxxxxxxxxxxxxxxxxxxxxx

==================================================================
BUG: KASAN: slab-use-after-free in list_add include/linux/list.h:192 [inline]
BUG: KASAN: slab-use-after-free in add_to_unconfirmed+0x367/0x8c0 fs/nfsd/nfs4state.c:3993
Read of size 8 at addr ffff888076b91860 by task nfsd/7883

CPU: 0 UID: 0 PID: 7883 Comm: nfsd Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/26/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_address_description+0x55/0x1e0 mm/kasan/report.c:378
 print_report+0x58/0x70 mm/kasan/report.c:482
 kasan_report+0x117/0x150 mm/kasan/report.c:595
 list_add include/linux/list.h:192 [inline]
 add_to_unconfirmed+0x367/0x8c0 fs/nfsd/nfs4state.c:3993
 nfsd4_exchange_id+0xc21/0x1350 fs/nfsd/nfs4state.c:4407
 nfsd4_proc_compound+0x145a/0x25b0 fs/nfsd/nfs4proc.c:3313
 nfsd_dispatch+0x33d/0x9b0 fs/nfsd/nfssvc.c:1038
 svc_process_common+0x1173/0x18c0 net/sunrpc/svc.c:1527
 svc_process+0x290/0x710 net/sunrpc/svc.c:1682
 svc_handle_xprt net/sunrpc/svc_xprt.c:886 [inline]
 svc_recv+0x2525/0x3280 net/sunrpc/svc_xprt.c:968
 nfsd+0x3a5/0xbb0 fs/nfsd/nfssvc.c:919
 kthread+0x38b/0x480 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>

Allocated by task 7644:
 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:409 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:426
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __kmalloc_cache_noprof+0x321/0x600 mm/slub.c:5563
 _kmalloc_noprof include/linux/slab.h:991 [inline]
 nfs4_state_create_net fs/nfsd/nfs4state.c:9736 [inline]
 nfs4_state_start_net+0x10c/0x1180 fs/nfsd/nfs4state.c:9834
 nfsd_startup_net fs/nfsd/nfssvc.c:391 [inline]
 nfsd_svc+0x481/0x710 fs/nfsd/nfssvc.c:775
 write_threads+0x434/0x610 fs/nfsd/nfsctl.c:438
 nfsctl_transaction_write+0x10f/0x160 fs/nfsd/nfsctl.c:114
 vfs_write+0x296/0xba0 fs/read_write.c:685
 ksys_write+0x150/0x270 fs/read_write.c:739
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 6123:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 kasan_save_free_info+0x40/0x50 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:264 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:296
 kasan_slab_free include/linux/kasan.h:235 [inline]
 slab_free_hook mm/slub.c:2748 [inline]
 slab_free mm/slub.c:6509 [inline]
 kfree+0x1c5/0x650 mm/slub.c:6802
 nfs4_state_destroy_net fs/nfsd/nfs4state.c:9823 [inline]
 nfs4_state_shutdown_net+0x774/0xa00 fs/nfsd/nfs4state.c:9908
 nfsd_shutdown_net fs/nfsd/nfssvc.c:421 [inline]
 nfsd_destroy_serv+0x25d/0x450 fs/nfsd/nfssvc.c:534
 nfsd_shutdown_threads+0x8c/0xd0 fs/nfsd/nfssvc.c:591
 nfsd_umount+0x41/0x60 fs/nfsd/nfsctl.c:1372
 deactivate_locked_super+0xbe/0x110 fs/super.c:586
 cleanup_mnt+0x3d3/0x460 fs/namespace.c:1317
 task_work_run+0x1d9/0x270 kernel/task_work.c:233
 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
 __exit_to_user_mode_loop kernel/entry/common.c:70 [inline]
 exit_to_user_mode_loop+0x204/0x770 kernel/entry/common.c:101
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:230 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:343 [inline]
 do_syscall_64+0x328/0x520 arch/x86/entry/syscall_64.c:89
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff888076b91800
 which belongs to the cache kmalloc-256 of size 256
The buggy address is located 96 bytes inside of
 freed 256-byte region [ffff888076b91800, ffff888076b91900)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff888076b90000 pfn:0x76b90
head: order:1 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0xfff00000000240(workingset|head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000240 ffff88801b041b40 ffffea0001e86410 ffffea00014c3b90
raw: ffff888076b90000 000000000010000a 00000000f5000000 0000000000000000
head: 00fff00000000240 ffff88801b041b40 ffffea0001e86410 ffffea00014c3b90
head: ffff888076b90000 000000000010000a 00000000f5000000 0000000000000000
head: 00fff00000000001 ffffffffffffff81 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000002
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 1, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 5615, tgid 5615 (syz-executor), ts 88616580147
 set_page_owner include/linux/page_owner.h:33 [inline]
 post_alloc_hook+0x1f9/0x250 mm/page_alloc.c:1871
 prep_new_page mm/page_alloc.c:1879 [inline]
 get_page_from_freelist+0x2209/0x2280 mm/page_alloc.c:3943
 __alloc_frozen_pages_noprof+0x217/0x5a0 mm/page_alloc.c:5436
 alloc_slab_page mm/slub.c:3347 [inline]
 allocate_slab+0x7d/0x620 mm/slub.c:3462
 new_slab mm/slub.c:3513 [inline]
 refill_objects+0x2d5/0x350 mm/slub.c:7418
 refill_sheaf mm/slub.c:2885 [inline]
 __pcs_replace_empty_main+0x2c8/0x6c0 mm/slub.c:4774
 alloc_from_pcs mm/slub.c:4850 [inline]
 slab_alloc_node mm/slub.c:4984 [inline]
 __do_kmalloc_node mm/slub.c:5413 [inline]
 __kmalloc_noprof+0x47b/0x720 mm/slub.c:5439
 _kmalloc_noprof include/linux/slab.h:995 [inline]
 _kzalloc_noprof include/linux/slab.h:1312 [inline]
 new_dir fs/proc/proc_sysctl.c:965 [inline]
 get_subdir fs/proc/proc_sysctl.c:1009 [inline]
 sysctl_mkdir_p fs/proc/proc_sysctl.c:1319 [inline]
 __register_sysctl_table+0xc02/0x1370 fs/proc/proc_sysctl.c:1394
 neigh_sysctl_register+0x9b1/0xa90 net/core/neighbour.c:3932
 devinet_sysctl_register+0xad/0x200 net/ipv4/devinet.c:2782
 inetdev_init+0x29e/0x4d0 net/ipv4/devinet.c:291
 inetdev_event+0x307/0x15e0 net/ipv4/devinet.c:1590
 notifier_call_chain+0x1a5/0x3d0 kernel/notifier.c:85
 call_netdevice_notifiers_extack net/core/dev.c:2313 [inline]
 call_netdevice_notifiers net/core/dev.c:2327 [inline]
 register_netdevice+0x18a4/0x1eb0 net/core/dev.c:11584
 macvlan_common_newlink+0x12e5/0x1a50 drivers/net/macvlan.c:1575
 rtnl_newlink_create+0x305/0x7b0 net/core/rtnetlink.c:3974
page last free pid 5615 tgid 5615 ts 88569600911 stack trace:
 reset_page_owner include/linux/page_owner.h:26 [inline]
 __free_pages_prepare mm/page_alloc.c:1418 [inline]
 __free_frozen_pages+0xc93/0xd90 mm/page_alloc.c:2962
 __slab_free+0x274/0x2c0 mm/slub.c:5823
 qlink_free mm/kasan/quarantine.c:163 [inline]
 qlist_free_all+0x99/0x100 mm/kasan/quarantine.c:179
 kasan_quarantine_reduce+0x148/0x160 mm/kasan/quarantine.c:286
 __kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:361
 kasan_slab_alloc include/linux/kasan.h:253 [inline]
 slab_post_alloc_hook mm/slub.c:4683 [inline]
 slab_alloc_node mm/slub.c:4996 [inline]
 kmem_cache_alloc_node_noprof+0x354/0x610 mm/slub.c:5068
 __alloc_skb+0x1db/0x7a0 net/core/skbuff.c:704
 alloc_skb include/linux/skbuff.h:1384 [inline]
 nlmsg_new include/net/netlink.h:1055 [inline]
 netlink_ack+0x136/0xb30 net/netlink/af_netlink.c:2512
 netlink_rcv_skb+0x2a4/0x4a0 net/netlink/af_netlink.c:2581
 netlink_unicast_kernel net/netlink/af_netlink.c:1338 [inline]
 netlink_unicast+0x7bd/0x940 net/netlink/af_netlink.c:1364
 netlink_sendmsg+0x813/0xb40 net/netlink/af_netlink.c:1919
 sock_sendmsg_nosec+0x13a/0x180 net/socket.c:800
 __sock_sendmsg net/socket.c:815 [inline]
 __sys_sendto+0x408/0x5a0 net/socket.c:2281
 __do_sys_sendto net/socket.c:2288 [inline]
 __se_sys_sendto net/socket.c:2284 [inline]
 __x64_sys_sendto+0xde/0x100 net/socket.c:2284
 do_syscall_x64 arch/x86/entry/syscall_64.c:61 [inline]
 do_syscall_64+0x166/0x520 arch/x86/entry/syscall_64.c:84
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff888076b91700: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888076b91780: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888076b91800: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                                                       ^
 ffff888076b91880: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888076b91900: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


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