[moderation] [nfs?] KASAN: slab-out-of-bounds Read in nfsd

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: f5098b6bae76 Linux 7.2-rc5
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17757fde580000
kernel config: https://syzkaller.appspot.com/x/.config?x=cb17729fb04b1e3a
dashboard link: https://syzkaller.appspot.com/bug?extid=22fbae706aee71c5fe06
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
CC: [Dai...@oracle.com c...@kernel.org jla...@kernel.org linux-...@vger.kernel.org linu...@vger.kernel.org ne...@brown.name okor...@redhat.com t...@talpey.com]

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/0950bde8674a/disk-f5098b6b.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/4f6b46d162d4/vmlinux-f5098b6b.xz
kernel image: https://storage.googleapis.com/syzbot-assets/97f60961986e/bzImage-f5098b6b.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+22fbae...@syzkaller.appspotmail.com

=========[ 412.535945][ T8659] ==================================================================
BUG: KASAN: slab-out-of-bounds in nfsd+0x118/0xbc0 fs/nfsd/nfssvc.c:888
Read of size 8 at addr ffff88802ba84f50 by task nfsd/8659

CPU: 1 UID: 0 PID: 8659 Comm: nfsd Not tainted syzkaller #0 PREEMPT_{RT,(full)}
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
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
nfsd+0x118/0xbc0 fs/nfsd/nfssvc.c:888
kthread+0x388/0x470 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 8641:
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+0x3d2/0x6b0 mm/slub.c:5489
_kmalloc_noprof include/linux/slab.h:988 [inline]
_kzalloc_noprof include/linux/slab.h:1309 [inline]
__svc_create+0x63/0x9e0 net/sunrpc/svc.c:491
svc_create_pooled+0x5ad/0x770 net/sunrpc/svc.c:585
nfsd_create_serv+0x55f/0x840 fs/nfsd/nfssvc.c:616
__write_ports_addfd fs/nfsd/nfsctl.c:737 [inline]
__write_ports fs/nfsd/nfsctl.c:805 [inline]
write_ports+0x6a2/0xd20 fs/nfsd/nfsctl.c:861
nfsctl_transaction_write+0x112/0x160 fs/nfsd/nfsctl.c:112
vfs_write+0x29f/0xbb0 fs/read_write.c:685
ksys_write+0x156/0x270 fs/read_write.c:739
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff88802ba84c00
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 376 bytes to the right of
allocated 472-byte region [ffff88802ba84c00, ffff88802ba84dd8)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff88802ba87400 pfn:0x2ba84
head: order:2 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0x80000000000240(workingset|head|node=0|zone=1)
page_type: f5(slab)
raw: 0080000000000240 ffff88813ffb1c80 ffffea0001841610 ffffea0000b39a10
raw: ffff88802ba87400 000000080010000f 00000000f5000000 0000000000000000
head: 0080000000000240 ffff88813ffb1c80 ffffea0001841610 ffffea0000b39a10
head: ffff88802ba87400 000000080010000f 00000000f5000000 0000000000000000
head: 0080000000000002 ffffffffffffff01 00000000ffffffff 00000000ffffffff
head: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000004
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 2, migratetype Unmovable, gfp_mask 0xd2820(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 744, tgid 744 (kworker/u8:7), ts 159616203074, free_ts 101842806731
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x1f9/0x250 mm/page_alloc.c:1859
prep_new_page mm/page_alloc.c:1867 [inline]
get_page_from_freelist+0x262a/0x26a0 mm/page_alloc.c:3946
__alloc_frozen_pages_noprof+0x18d/0x380 mm/page_alloc.c:5304
alloc_slab_page mm/slub.c:3266 [inline]
allocate_slab+0x79/0x5e0 mm/slub.c:3380
new_slab mm/slub.c:3426 [inline]
refill_objects+0x2d8/0x350 mm/slub.c:7310
refill_sheaf mm/slub.c:2804 [inline]
__pcs_replace_empty_main+0x330/0x690 mm/slub.c:4675
alloc_from_pcs mm/slub.c:4773 [inline]
slab_alloc_node mm/slub.c:4905 [inline]
__kmalloc_cache_noprof+0x468/0x6b0 mm/slub.c:5485
_kmalloc_noprof include/linux/slab.h:988 [inline]
batadv_forw_packet_alloc+0x178/0x370 net/batman-adv/send.c:506
batadv_iv_ogm_aggregate_new net/batman-adv/bat_iv_ogm.c:584 [inline]
batadv_iv_ogm_queue_add+0x8a9/0xd80 net/batman-adv/bat_iv_ogm.c:698
batadv_iv_ogm_schedule_buff net/batman-adv/bat_iv_ogm.c:870 [inline]
batadv_iv_ogm_schedule+0x84e/0xfa0 net/batman-adv/bat_iv_ogm.c:918
batadv_iv_send_outstanding_bat_ogm_packet+0x67a/0x790 net/batman-adv/bat_iv_ogm.c:1807
process_one_work kernel/workqueue.c:3322 [inline]
process_scheduled_works+0xa8e/0x14e0 kernel/workqueue.c:3405
worker_thread+0xa47/0xfb0 kernel/workqueue.c:3486
kthread+0x388/0x470 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
page last free pid 5742 tgid 5742 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
__free_pages_prepare mm/page_alloc.c:1406 [inline]
__free_frozen_pages+0x10e7/0x11c0 mm/page_alloc.c:2950
__slab_free+0x252/0x2a0 mm/slub.c:5741
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:350
kasan_slab_alloc include/linux/kasan.h:253 [inline]
slab_post_alloc_hook mm/slub.c:4584 [inline]
slab_alloc_node mm/slub.c:4917 [inline]
__do_kmalloc_node mm/slub.c:5333 [inline]
__kvmalloc_node_noprof+0x54f/0x8a0 mm/slub.c:6905
seq_buf_alloc fs/seq_file.c:39 [inline]
seq_read_iter+0x1eb/0xcb0 fs/seq_file.c:211
new_sync_read fs/read_write.c:493 [inline]
vfs_read+0x59e/0xa90 fs/read_write.c:574
ksys_read+0x156/0x270 fs/read_write.c:716
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
ffff88802ba84e00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88802ba84e80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88802ba84f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
^
ffff88802ba84f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88802ba85000: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
==================================================================


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