[syzbot] [net?] [nfs?] KASAN: slab-out-of-bounds Read in cache_seq_start_rcu

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: b4e07588e743 tracing: tell git to ignore the generated 'un..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=14b522d2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=45528449ee7e2c2f
dashboard link: https://syzkaller.appspot.com/bug?extid=60cfa08822470bbebe44
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13f52c36580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=13432cce580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/c05a9c593011/disk-b4e07588.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/779dda6a7608/vmlinux-b4e07588.xz
kernel image: https://storage.googleapis.com/syzbot-assets/5e7d794a3ff0/bzImage-b4e07588.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+60cfa0...@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-out-of-bounds in __cache_seq_start net/sunrpc/cache.c:1351 [inline]
BUG: KASAN: slab-out-of-bounds in cache_seq_start_rcu+0x3fe/0x420 net/sunrpc/cache.c:1399
Read of size 8 at addr ffff88802ae92800 by task syz.0.17/6044

CPU: 1 UID: 0 PID: 6044 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/18/2026
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:94 [inline]
dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
print_address_description mm/kasan/report.c:378 [inline]
print_report+0x13d/0x4b0 mm/kasan/report.c:482
kasan_report+0xdf/0x1d0 mm/kasan/report.c:595
__cache_seq_start net/sunrpc/cache.c:1351 [inline]
cache_seq_start_rcu+0x3fe/0x420 net/sunrpc/cache.c:1399
seq_read_iter+0x2c1/0x1270 fs/seq_file.c:226
seq_read+0x33b/0x4c0 fs/seq_file.c:163
pde_read fs/proc/inode.c:308 [inline]
proc_reg_read+0x240/0x330 fs/proc/inode.c:320
vfs_read+0x1e4/0xb30 fs/read_write.c:572
ksys_pread64 fs/read_write.c:765 [inline]
__do_sys_pread64 fs/read_write.c:773 [inline]
__se_sys_pread64 fs/read_write.c:770 [inline]
__x64_sys_pread64+0x1eb/0x250 fs/read_write.c:770
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x10b/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f88b8d9c819
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:00007ffc567f4a98 EFLAGS: 00000246 ORIG_RAX: 0000000000000011
RAX: ffffffffffffffda RBX: 00007f88b9015fa0 RCX: 00007f88b8d9c819
RDX: 0000000000000566 RSI: 0000000000000000 RDI: 0000000000000003
RBP: 00007f88b8e32c91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000080000002 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f88b9015fac R14: 00007f88b9015fa0 R15: 00007f88b9015fa0
</TASK>

Allocated by task 5958:
kasan_save_stack+0x30/0x50 mm/kasan/common.c:57
kasan_save_track+0x14/0x30 mm/kasan/common.c:78
poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
__kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:415
kasan_kmalloc include/linux/kasan.h:263 [inline]
__do_kmalloc_node mm/slub.c:5295 [inline]
__kmalloc_noprof+0x301/0x850 mm/slub.c:5307
kmalloc_noprof include/linux/slab.h:954 [inline]
kzalloc_noprof include/linux/slab.h:1188 [inline]
cache_create_net+0xa2/0x1f0 net/sunrpc/cache.c:1733
nfsd_export_init+0x62/0x250 fs/nfsd/export.c:1536
nfsd_net_init+0x69/0x3e0 fs/nfsd/nfsctl.c:2209
ops_init+0x1e2/0x5f0 net/core/net_namespace.c:137
setup_net+0x118/0x3a0 net/core/net_namespace.c:446
copy_net_ns+0x46f/0x7c0 net/core/net_namespace.c:579
create_new_namespaces+0x3ea/0xac0 kernel/nsproxy.c:132
unshare_nsproxy_namespaces+0xf2/0x220 kernel/nsproxy.c:234
ksys_unshare+0x438/0xab0 kernel/fork.c:3245
__do_sys_unshare kernel/fork.c:3319 [inline]
__se_sys_unshare kernel/fork.c:3317 [inline]
__x64_sys_unshare+0x31/0x40 kernel/fork.c:3317
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x10b/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff88802ae92000
which belongs to the cache kmalloc-2k of size 2048
The buggy address is located 0 bytes to the right of
allocated 2048-byte region [ffff88802ae92000, ffff88802ae92800)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x2ae90
head: order:3 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88813fe86000 dead000000000100 dead000000000122
raw: 0000000000000000 0000000800080008 00000000f5000000 0000000000000000
head: 00fff00000000040 ffff88813fe86000 dead000000000100 dead000000000122
head: 0000000000000000 0000000800080008 00000000f5000000 0000000000000000
head: 00fff00000000003 fffffffffffffe01 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000008
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 3, migratetype Unmovable, gfp_mask 0xd20c0(__GFP_IO|__GFP_FS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP|__GFP_NOMEMALLOC), pid 5958, tgid 5958 (syz-executor), ts 108313513495, free_ts 108309100167
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x153/0x170 mm/page_alloc.c:1858
prep_new_page mm/page_alloc.c:1866 [inline]
get_page_from_freelist+0x11a6/0x33b0 mm/page_alloc.c:3946
__alloc_frozen_pages_noprof+0x27c/0x2bc0 mm/page_alloc.c:5226
alloc_slab_page mm/slub.c:3278 [inline]
allocate_slab mm/slub.c:3467 [inline]
new_slab+0xa6/0x6c0 mm/slub.c:3525
refill_objects+0x277/0x420 mm/slub.c:7251
refill_sheaf mm/slub.c:2816 [inline]
__pcs_replace_empty_main+0x375/0x650 mm/slub.c:4651
alloc_from_pcs mm/slub.c:4749 [inline]
slab_alloc_node mm/slub.c:4883 [inline]
__kmalloc_cache_noprof+0x493/0x6f0 mm/slub.c:5410
kmalloc_noprof include/linux/slab.h:950 [inline]
netdev_create_hash net/core/dev.c:12922 [inline]
netdev_init+0x151/0x3c0 net/core/dev.c:12942
ops_init+0x1e2/0x5f0 net/core/net_namespace.c:137
setup_net+0x118/0x3a0 net/core/net_namespace.c:446
copy_net_ns+0x46f/0x7c0 net/core/net_namespace.c:579
create_new_namespaces+0x3ea/0xac0 kernel/nsproxy.c:132
unshare_nsproxy_namespaces+0xf2/0x220 kernel/nsproxy.c:234
ksys_unshare+0x438/0xab0 kernel/fork.c:3245
__do_sys_unshare kernel/fork.c:3319 [inline]
__se_sys_unshare kernel/fork.c:3317 [inline]
__x64_sys_unshare+0x31/0x40 kernel/fork.c:3317
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x10b/0xf80 arch/x86/entry/syscall_64.c:94
page last free pid 5958 tgid 5958 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
__free_pages_prepare mm/page_alloc.c:1402 [inline]
__free_frozen_pages+0x747/0x1040 mm/page_alloc.c:2943
qlink_free mm/kasan/quarantine.c:163 [inline]
qlist_free_all+0x47/0xf0 mm/kasan/quarantine.c:179
kasan_quarantine_reduce+0x1a0/0x1f0 mm/kasan/quarantine.c:286
__kasan_slab_alloc+0x69/0x90 mm/kasan/common.c:350
kasan_slab_alloc include/linux/kasan.h:253 [inline]
slab_post_alloc_hook mm/slub.c:4569 [inline]
slab_alloc_node mm/slub.c:4898 [inline]
kmem_cache_alloc_node_noprof+0x25a/0x6f0 mm/slub.c:4950
__alloc_skb+0x140/0x710 net/core/skbuff.c:702
alloc_skb include/linux/skbuff.h:1383 [inline]
nlmsg_new include/net/netlink.h:1055 [inline]
netlink_ack+0x117/0xb80 net/netlink/af_netlink.c:2487
netlink_rcv_skb+0x333/0x420 net/netlink/af_netlink.c:2556
netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline]
netlink_unicast+0x585/0x850 net/netlink/af_netlink.c:1344
netlink_sendmsg+0x8b0/0xda0 net/netlink/af_netlink.c:1894
sock_sendmsg_nosec net/socket.c:787 [inline]
__sock_sendmsg net/socket.c:802 [inline]
__sys_sendto+0x468/0x4b0 net/socket.c:2265
__do_sys_sendto net/socket.c:2272 [inline]
__se_sys_sendto net/socket.c:2268 [inline]
__x64_sys_sendto+0xe0/0x1c0 net/socket.c:2268
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x10b/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
ffff88802ae92700: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
ffff88802ae92780: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
>ffff88802ae92800: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
^
ffff88802ae92880: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
ffff88802ae92900: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

[Jeongjun Park]

#syz test upstream master

---
net/sunrpc/cache.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
index 7081c1214e6c..218994cd76fc 100644
--- a/net/sunrpc/cache.c
+++ b/net/sunrpc/cache.c
@@ -1357,6 +1357,9 @@ static void *__cache_seq_start(struct seq_file *m, loff_t *pos)
hlist_first_rcu(&cd->hash_table[hash])),
struct cache_head, cache_list);

+ if (hash >= cd->hash_size)
+ return NULL;
+
*pos = ((long long)hash << 32) + 1;
return ch;
}
--

[Jeongjun Park]

#syz test upstream master

---
net/sunrpc/cache.c | 3 +++
1 file changed, 3 insertions(+)

diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c

index 7081c1214e6c..8cb14838c654 100644

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+60cfa0...@syzkaller.appspotmail.com
Tested-by: syzbot+60cfa0...@syzkaller.appspotmail.com

Tested on:

commit: 4ee64205 Merge tag 'clk-for-linus' of git://git.kernel..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1126d702580000

kernel config: https://syzkaller.appspot.com/x/.config?x=45528449ee7e2c2f
dashboard link: https://syzkaller.appspot.com/bug?extid=60cfa08822470bbebe44
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44

patch: https://syzkaller.appspot.com/x/patch.diff?x=17c322d2580000

Note: testing is done by a robot and is best-effort only.