Subject: [syzbot] [netfilter?] KASAN: slab-out-of-bounds Read in nfacct_mt_checkentry

From: syzbot <[email-masked]>
Date: Thu, 17 Jul 2025 18:06:28 -0700

Hello,

syzbot found the following issue on:

HEAD commit:    5d5d62298b8b Merge tag 'x86_urgent_for_v6.16_rc6' of git:/..
git tree:       upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=1655418c580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=b309c907eaab29da
dashboard link: https://syzkaller.appspot.com/bug?extid=4ff165b9251e4d295690
compiler:       Debian clang version 20.1.7 (++20250616065708+6146a88f6049-1~exp1~20250616065826.132), Debian LLD 20.1.7
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=156787d4580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=136787d4580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/621a2e2bbe6e/disk-5d5d6229.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/1822022cd8cb/vmlinux-5d5d6229.xz
kernel image: https://storage.googleapis.com/syzbot-assets/10cee653a6cd/bzImage-5d5d6229.xz

The issue was bisected to:

commit 6001a930ce0378b62210d4f83583fc88a903d89d
Author: Pablo Neira Ayuso <[email-masked]>
Date:   Mon Feb 15 11:28:07 2021 +0000

    netfilter: nftables: introduce table ownership

bisection log:  https://syzkaller.appspot.com/x/bisect.txt?x=133e518c580000
final oops:     https://syzkaller.appspot.com/x/report.txt?x=10be518c580000
console output: https://syzkaller.appspot.com/x/log.txt?x=173e518c580000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email-masked]
Fixes: 6001a930ce03 ("netfilter: nftables: introduce table ownership")

==================================================================
BUG: KASAN: slab-out-of-bounds in string_nocheck lib/vsprintf.c:639 [inline]
BUG: KASAN: slab-out-of-bounds in string+0x231/0x2b0 lib/vsprintf.c:721
Read of size 1 at addr ffff88801eac95c8 by task syz-executor183/5851

CPU: 0 UID: 0 PID: 5851 Comm: syz-executor183 Not tainted 6.16.0-rc5-syzkaller-00276-g5d5d62298b8b #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xca/0x230 mm/kasan/report.c:480
 kasan_report+0x118/0x150 mm/kasan/report.c:593
 string_nocheck lib/vsprintf.c:639 [inline]
 string+0x231/0x2b0 lib/vsprintf.c:721
 vsnprintf+0x739/0xf00 lib/vsprintf.c:2874
 vprintk_store+0x3c7/0xd00 kernel/printk/printk.c:2279
 vprintk_emit+0x21e/0x7a0 kernel/printk/printk.c:2426
 _printk+0xcf/0x120 kernel/printk/printk.c:2475
 nfacct_mt_checkentry+0xd2/0xe0 net/netfilter/xt_nfacct.c:41
 xt_check_match+0x3d1/0xab0 net/netfilter/x_tables.c:523
 __nft_match_init+0x63a/0x840 net/netfilter/nft_compat.c:520
 nf_tables_newexpr net/netfilter/nf_tables_api.c:3493 [inline]
 nf_tables_newrule+0x178c/0x2890 net/netfilter/nf_tables_api.c:4324
 nfnetlink_rcv_batch net/netfilter/nfnetlink.c:525 [inline]
 nfnetlink_rcv_skb_batch net/netfilter/nfnetlink.c:648 [inline]
 nfnetlink_rcv+0x1132/0x2520 net/netfilter/nfnetlink.c:666
 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
 netlink_unicast+0x759/0x8e0 net/netlink/af_netlink.c:1346
 netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1896
 sock_sendmsg_nosec net/socket.c:712 [inline]
 __sock_sendmsg+0x219/0x270 net/socket.c:727
 ____sys_sendmsg+0x505/0x830 net/socket.c:2566
 ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2620
 __sys_sendmsg net/socket.c:2652 [inline]
 __do_sys_sendmsg net/socket.c:2657 [inline]
 __se_sys_sendmsg net/socket.c:2655 [inline]
 __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2655
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fa7bbf1c6a9
Code: 48 83 c4 28 c3 e8 37 17 00 00 0f 1f 80 00 00 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 b8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fff7139c908 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007fff7139cad8 RCX: 00007fa7bbf1c6a9
RDX: 0000000000000000 RSI: 0000200000000000 RDI: 0000000000000003
RBP: 00007fa7bbf8f610 R08: 0000000000000002 R09: 00007fff7139cad8
R10: 0000000000000009 R11: 0000000000000246 R12: 0000000000000001
R13: 00007fff7139cac8 R14: 0000000000000001 R15: 0000000000000001
 </TASK>

Allocated by task 5851:
 kasan_save_stack mm/kasan/common.c:47 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:68
 poison_kmalloc_redzone mm/kasan/common.c:377 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:394
 kasan_kmalloc include/linux/kasan.h:260 [inline]
 __do_kmalloc_node mm/slub.c:4328 [inline]
 __kmalloc_noprof+0x27a/0x4f0 mm/slub.c:4340
 kmalloc_noprof include/linux/slab.h:909 [inline]
 kzalloc_noprof include/linux/slab.h:1039 [inline]
 nf_tables_newrule+0x1506/0x2890 net/netfilter/nf_tables_api.c:4306
 nfnetlink_rcv_batch net/netfilter/nfnetlink.c:525 [inline]
 nfnetlink_rcv_skb_batch net/netfilter/nfnetlink.c:648 [inline]
 nfnetlink_rcv+0x1132/0x2520 net/netfilter/nfnetlink.c:666
 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
 netlink_unicast+0x759/0x8e0 net/netlink/af_netlink.c:1346
 netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1896
 sock_sendmsg_nosec net/socket.c:712 [inline]
 __sock_sendmsg+0x219/0x270 net/socket.c:727
 ____sys_sendmsg+0x505/0x830 net/socket.c:2566
 ___sys_sendmsg+0x21f/0x2a0 net/socket.c:2620
 __sys_sendmsg net/socket.c:2652 [inline]
 __do_sys_sendmsg net/socket.c:2657 [inline]
 __se_sys_sendmsg net/socket.c:2655 [inline]
 __x64_sys_sendmsg+0x19b/0x260 net/socket.c:2655
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff88801eac9580
 which belongs to the cache kmalloc-cg-96 of size 96
The buggy address is located 0 bytes to the right of
 allocated 72-byte region [ffff88801eac9580, ffff88801eac95c8)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1eac9
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000000 ffff88801a449640 dead000000000122 0000000000000000
raw: 0000000000000000 0000000080200020 00000000f5000000 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 0, migratetype Unmovable, gfp_mask 0x52cc0(GFP_KERNEL|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP), pid 1, tgid 1 (swapper/0), ts 2776913905, free_ts 0
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x240/0x2a0 mm/page_alloc.c:1704
 prep_new_page mm/page_alloc.c:1712 [inline]
 get_page_from_freelist+0x21e4/0x22c0 mm/page_alloc.c:3669
 __alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:4959
 alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2419
 alloc_slab_page mm/slub.c:2451 [inline]
 allocate_slab+0x8a/0x3b0 mm/slub.c:2619
 new_slab mm/slub.c:2673 [inline]
 ___slab_alloc+0xbfc/0x1480 mm/slub.c:3859
 __slab_alloc mm/slub.c:3949 [inline]
 __slab_alloc_node mm/slub.c:4024 [inline]
 slab_alloc_node mm/slub.c:4185 [inline]
 __do_kmalloc_node mm/slub.c:4327 [inline]
 __kmalloc_noprof+0x305/0x4f0 mm/slub.c:4340
 kmalloc_noprof include/linux/slab.h:909 [inline]
 kzalloc_noprof include/linux/slab.h:1039 [inline]
 __register_sysctl_table+0x72/0x1340 fs/proc/proc_sysctl.c:1380
 user_namespace_sysctl_init+0x25/0x150 kernel/ucount.c:355
 do_one_initcall+0x233/0x820 init/main.c:1274
 do_initcall_level+0x137/0x1f0 init/main.c:1336
 do_initcalls+0x69/0xd0 init/main.c:1352
 kernel_init_freeable+0x3d9/0x570 init/main.c:1584
 kernel_init+0x1d/0x1d0 init/main.c:1474
 ret_from_fork+0x3fc/0x770 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
page_owner free stack trace missing

Memory state around the buggy address:
 ffff88801eac9480: 00 00 00 00 00 00 00 00 00 00 00 00 fc fc fc fc
 ffff88801eac9500: 00 00 00 00 00 00 00 00 00 00 00 00 fc fc fc fc
>ffff88801eac9580: 00 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc
                                              ^
 ffff88801eac9600: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff88801eac9680: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================

---
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