[v6.6] KASAN: slab-use-after-free Read in nfsd_svc

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: c5596480c50e Linux 6.6.145
git tree: linux-6.6.y
console output: https://syzkaller.appspot.com/x/log.txt?x=10f97fde580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f0bc3d90c30838b5
dashboard link: https://syzkaller.appspot.com/bug?extid=c0081e36d956ba121a48
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/eb5cda0a8020/disk-c5596480.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ca05ff2fc502/vmlinux-c5596480.xz
kernel image: https://storage.googleapis.com/syzbot-assets/6daf3255b985/bzImage-c5596480.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c0081e...@syzkaller.appspotmail.com

svc: failed to register nfsdv3 RPC service (errno 111).
svc: failed to register nfsaclv3 RPC service (errno 111).
==================================================================
BUG: KASAN: slab-use-after-free in nfsd_svc+0x99a/0xab0 fs/nfsd/nfssvc.c:818
Read of size 4 at addr ffff88805cc89c54 by task syz.2.84/6096

CPU: 0 PID: 6096 Comm: syz.2.84 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
Call Trace:
<TASK>
dump_stack_lvl+0x18c/0x250 lib/dump_stack.c:106
print_address_description mm/kasan/report.c:364 [inline]
print_report+0xa8/0x210 mm/kasan/report.c:468
kasan_report+0x117/0x150 mm/kasan/report.c:581
nfsd_svc+0x99a/0xab0 fs/nfsd/nfssvc.c:818
write_threads+0x393/0x510 fs/nfsd/nfsctl.c:417
nfsctl_transaction_write+0x10c/0x150 fs/nfsd/nfsctl.c:113
vfs_write+0x299/0x9a0 fs/read_write.c:582
ksys_write+0x151/0x260 fs/read_write.c:637
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f2f41f9de99
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:00007f2f42e1b028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f2f42225fa0 RCX: 00007f2f41f9de99
RDX: 0000000000000002 RSI: 0000200000000100 RDI: 0000000000000003
RBP: 00007f2f42033eaf R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f2f42226038 R14: 00007f2f42225fa0 R15: 00007ffc2a66df38
</TASK>

Allocated by task 6096:
kasan_save_stack mm/kasan/common.c:46 [inline]
kasan_set_track+0x4e/0x70 mm/kasan/common.c:53
____kasan_kmalloc mm/kasan/common.c:375 [inline]
__kasan_kmalloc+0x8f/0xa0 mm/kasan/common.c:384
kmalloc include/linux/slab.h:600 [inline]
kzalloc include/linux/slab.h:721 [inline]
__svc_create+0x60/0xa20 net/sunrpc/svc.c:464
svc_create_pooled+0x66a/0x7e0 net/sunrpc/svc.c:556
nfsd_create_serv+0x29f/0x5c0 fs/nfsd/nfssvc.c:672
nfsd_svc+0x183/0xab0 fs/nfsd/nfssvc.c:801
write_threads+0x393/0x510 fs/nfsd/nfsctl.c:417
nfsctl_transaction_write+0x10c/0x150 fs/nfsd/nfsctl.c:113
vfs_write+0x299/0x9a0 fs/read_write.c:582
ksys_write+0x151/0x260 fs/read_write.c:637
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2

Freed by task 6096:
kasan_save_stack mm/kasan/common.c:46 [inline]
kasan_set_track+0x4e/0x70 mm/kasan/common.c:53
kasan_save_free_info+0x28/0x40 mm/kasan/generic.c:522
____kasan_slab_free+0x126/0x1f0 mm/kasan/common.c:237
kasan_slab_free include/linux/kasan.h:164 [inline]
slab_free_hook mm/slub.c:1811 [inline]
slab_free_freelist_hook+0x130/0x1a0 mm/slub.c:1837
slab_free mm/slub.c:3830 [inline]
__kmem_cache_free+0xba/0x1f0 mm/slub.c:3843
kref_put include/linux/kref.h:65 [inline]
svc_put include/linux/sunrpc/svc.h:124 [inline]
nfsd_svc+0x762/0xab0 fs/nfsd/nfssvc.c:816
write_threads+0x393/0x510 fs/nfsd/nfsctl.c:417
nfsctl_transaction_write+0x10c/0x150 fs/nfsd/nfsctl.c:113
vfs_write+0x299/0x9a0 fs/read_write.c:582
ksys_write+0x151/0x260 fs/read_write.c:637
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2

Last potentially related work creation:
kasan_save_stack+0x3e/0x60 mm/kasan/common.c:46
__kasan_record_aux_stack+0xaf/0xc0 mm/kasan/generic.c:492
__call_rcu_common kernel/rcu/tree.c:2721 [inline]
call_rcu+0x153/0x900 kernel/rcu/tree.c:2837
fib6_info_release include/net/ip6_fib.h:349 [inline]
ip6_route_info_create+0xa0d/0x1260 net/ipv6/route.c:3887
ip6_route_add+0x28/0x160 net/ipv6/route.c:3901
addrconf_add_mroute net/ipv6/addrconf.c:2534 [inline]
addrconf_add_dev+0x29c/0x3b0 net/ipv6/addrconf.c:2552
inet6_addr_add+0x25d/0xb30 net/ipv6/addrconf.c:3025
inet6_rtm_newaddr+0x6fd/0x9d0 net/ipv6/addrconf.c:5043
rtnetlink_rcv_msg+0x843/0xf90 net/core/rtnetlink.c:6484
netlink_rcv_skb+0x235/0x4c0 net/netlink/af_netlink.c:2550
netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
netlink_unicast+0x7b1/0x930 net/netlink/af_netlink.c:1346
netlink_sendmsg+0x8d0/0xbf0 net/netlink/af_netlink.c:1899
sock_sendmsg_nosec net/socket.c:730 [inline]
__sock_sendmsg net/socket.c:745 [inline]
__sys_sendto+0x4a9/0x6b0 net/socket.c:2201
__do_sys_sendto net/socket.c:2213 [inline]
__se_sys_sendto net/socket.c:2209 [inline]
__x64_sys_sendto+0xde/0xf0 net/socket.c:2209
do_syscall_x64 arch/x86/entry/common.c:46 [inline]
do_syscall_64+0x55/0xb0 arch/x86/entry/common.c:76
entry_SYSCALL_64_after_hwframe+0x68/0xd2

The buggy address belongs to the object at ffff88805cc89c00
which belongs to the cache kmalloc-512 of size 512
The buggy address is located 84 bytes inside of
freed 512-byte region [ffff88805cc89c00, ffff88805cc89e00)

The buggy address belongs to the physical page:
page:ffffea0001732200 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x5cc88
head:ffffea0001732200 order:2 entire_mapcount:0 nr_pages_mapped:0 pincount:0
anon flags: 0xfff00000000840(slab|head|node=0|zone=1|lastcpupid=0x7ff)
page_type: 0xffffffff()
raw: 00fff00000000840 ffff888017c41c80 0000000000000000 dead000000000001
raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 2, migratetype Unmovable, gfp_mask 0x52820(GFP_ATOMIC|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP), pid 49, tgid 49 (kworker/u4:3), ts 90072845238, free_ts 30131993086
set_page_owner include/linux/page_owner.h:31 [inline]
post_alloc_hook+0x1c1/0x200 mm/page_alloc.c:1582
prep_new_page mm/page_alloc.c:1589 [inline]
get_page_from_freelist+0x2181/0x22a0 mm/page_alloc.c:3221
__alloc_pages+0x1f0/0x460 mm/page_alloc.c:4501
alloc_slab_page+0x5d/0x180 mm/slub.c:1881
allocate_slab mm/slub.c:2028 [inline]
new_slab+0x87/0x2d0 mm/slub.c:2081
___slab_alloc+0xc5c/0x12f0 mm/slub.c:3253
__slab_alloc mm/slub.c:3339 [inline]
__slab_alloc_node mm/slub.c:3392 [inline]
slab_alloc_node mm/slub.c:3485 [inline]
__kmem_cache_alloc_node+0x11f/0x250 mm/slub.c:3534
__do_kmalloc_node mm/slab_common.c:1006 [inline]
__kmalloc+0xa7/0x240 mm/slab_common.c:1020
kmalloc include/linux/slab.h:604 [inline]
kzalloc include/linux/slab.h:721 [inline]
fib6_info_alloc+0x30/0xf0 net/ipv6/ip6_fib.c:155
ip6_route_info_create+0x455/0x1260 net/ipv6/route.c:3805
ip6_route_add+0x28/0x160 net/ipv6/route.c:3901
addrconf_prefix_route net/ipv6/addrconf.c:2470 [inline]
addrconf_add_linklocal+0x44d/0x6d0 net/ipv6/addrconf.c:3316
addrconf_addr_gen+0x50e/0x620 net/ipv6/addrconf.c:3445
addrconf_dev_config net/ipv6/addrconf.c:3490 [inline]
addrconf_init_auto_addrs+0x720/0xac0 net/ipv6/addrconf.c:3569
addrconf_notify+0xb62/0x1010 net/ipv6/addrconf.c:3742
notifier_call_chain+0x18f/0x380 kernel/notifier.c:93
page last free stack trace:
reset_page_owner include/linux/page_owner.h:24 [inline]
free_pages_prepare mm/page_alloc.c:1182 [inline]
free_unref_page_prepare+0x7d7/0x8f0 mm/page_alloc.c:2366
free_unref_page+0x32/0x2e0 mm/page_alloc.c:2459
free_contig_range+0xa1/0x150 mm/page_alloc.c:6421
destroy_args+0x7d/0x840 mm/debug_vm_pgtable.c:1015
debug_vm_pgtable+0x411/0x440 mm/debug_vm_pgtable.c:1400
do_one_initcall+0x242/0x790 init/main.c:1249
do_initcall_level+0x13d/0x1f0 init/main.c:1311
do_initcalls+0x69/0xd0 init/main.c:1327
kernel_init_freeable+0x3d9/0x560 init/main.c:1564
kernel_init+0x1d/0x1c0 init/main.c:1454
ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293

Memory state around the buggy address:
ffff88805cc89b00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88805cc89b80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff88805cc89c00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
^
ffff88805cc89c80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
ffff88805cc89d00: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
==================================================================


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