Re: [syzbot] [net?] [nfc?] KASAN: slab-out-of-bounds Read in __dynamic_pr_debug

syzbot has found a reproducer for the following issue on:

HEAD commit:    21d6ac051080 Merge branch 'for-next/core' into for-kernelci
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
console output: https://syzkaller.appspot.com/x/log.txt?x=17d30179580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d1128bc53f2ef7f3
dashboard link: https://syzkaller.appspot.com/bug?extid=1e3df0852e82c21ca418
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
userspace arch: arm64
syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=13d43e79580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1746fa25580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/88380e2ddcb9/disk-21d6ac05.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/5dba5c2896b7/vmlinux-21d6ac05.xz
kernel image: https://storage.googleapis.com/syzbot-assets/52ac739e37e0/Image-21d6ac05.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email protected]

==================================================================
BUG: KASAN: slab-out-of-bounds in string_nocheck+0xd8/0x140 lib/vsprintf.c:648
Read of size 1 at addr ffff0000d0cf899c by task syz.0.17/4947

CPU: 1 UID: 0 PID: 4947 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/07/2026
Call trace:
 show_stack+0x2c/0x3c arch/arm64/kernel/stacktrace.c:499 (C)
 __dump_stack+0x30/0x40 lib/dump_stack.c:94
 dump_stack_lvl+0xd8/0x12c lib/dump_stack.c:120
 print_address_description+0xb0/0x238 mm/kasan/report.c:378
 print_report+0x68/0x84 mm/kasan/report.c:482
 kasan_report+0x8c/0xc4 mm/kasan/report.c:595
 __asan_report_load1_noabort+0x20/0x2c mm/kasan/report_generic.c:378
 string_nocheck+0xd8/0x140 lib/vsprintf.c:648
 string+0x8c/0xc8 lib/vsprintf.c:730
 vsnprintf+0x880/0xd10 lib/vsprintf.c:2945
 va_format lib/vsprintf.c:1725 [inline]
 pointer+0x5e8/0x6b4 lib/vsprintf.c:2573
 vsnprintf+0x618/0xd10 lib/vsprintf.c:2949
 vprintk_store+0x344/0xb94 kernel/printk/printk.c:2307
 vprintk_emit+0x1bc/0x514 kernel/printk/printk.c:2455
 vprintk_default+0x54/0x80 kernel/printk/printk.c:2494
 vprintk+0x9c/0x114 kernel/printk/printk_safe.c:82
 _printk+0xe0/0x130 kernel/printk/printk.c:2504
 __dynamic_pr_debug+0x148/0x1e4 lib/dynamic_debug.c:879
 nfc_llcp_wks_sap net/nfc/llcp_core.c:344 [inline]
 nfc_llcp_get_sdp_ssap+0x350/0x3fc net/nfc/llcp_core.c:420
 llcp_sock_bind+0x2e0/0x58c net/nfc/llcp_sock.c:114
 __sys_bind_socket net/socket.c:1920 [inline]
 __sys_bind+0x1c4/0x268 net/socket.c:1951
 __do_sys_bind net/socket.c:1956 [inline]
 __se_sys_bind net/socket.c:1954 [inline]
 __arm64_sys_bind+0x84/0x9c net/socket.c:1954
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
 do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
 el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:758
 el0t_64_sync_handler+0x44/0x104 arch/arm64/kernel/entry-common.c:777
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:590

Allocated by task 4947:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x40/0x78 mm/kasan/common.c:78
 kasan_save_alloc_info+0x40/0x50 mm/kasan/generic.c:570
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0x9c/0xb4 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:263 [inline]
 __do_kmalloc_node mm/slub.c:5334 [inline]
 __kmalloc_node_track_caller_noprof+0x434/0x6d4 mm/slub.c:5471
 kmemdup_noprof+0x44/0x8c mm/util.c:138
 kmemdup_noprof include/linux/fortify-string.h:715 [inline]
 llcp_sock_bind+0x2b0/0x58c net/nfc/llcp_sock.c:107
 __sys_bind_socket net/socket.c:1920 [inline]
 __sys_bind+0x1c4/0x268 net/socket.c:1951
 __do_sys_bind net/socket.c:1956 [inline]
 __se_sys_bind net/socket.c:1954 [inline]
 __arm64_sys_bind+0x84/0x9c net/socket.c:1954
 __invoke_syscall arch/arm64/kernel/syscall.c:35 [inline]
 invoke_syscall+0x98/0x244 arch/arm64/kernel/syscall.c:49
 el0_svc_common+0xec/0x23c arch/arm64/kernel/syscall.c:121
 do_el0_svc+0x4c/0x5c arch/arm64/kernel/syscall.c:140
 el0_svc+0x64/0x260 arch/arm64/kernel/entry-common.c:758
 el0t_64_sync_handler+0x44/0x104 arch/arm64/kernel/entry-common.c:777
 el0t_64_sync+0x198/0x19c arch/arm64/kernel/entry.S:590

The buggy address belongs to the object at ffff0000d0cf8980
 which belongs to the cache kmalloc-32 of size 32
The buggy address is located 0 bytes to the right of
 allocated 28-byte region [ffff0000d0cf8980, ffff0000d0cf899c)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x110cf8
flags: 0x5ffc00000000000(node=0|zone=2|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 05ffc00000000000 ffff0000c0001780 dead000000000100 dead000000000122
raw: 0000000000000000 0000000800400040 00000000f5000000 0000000000000000
page dumped because: kasan: bad access detected

Memory state around the buggy address:
 ffff0000d0cf8880: fa fb fb fb fc fc fc fc fa fb fb fb fc fc fc fc
 ffff0000d0cf8900: fa fb fb fb fc fc fc fc fa fb fb fb fc fc fc fc
>ffff0000d0cf8980: 00 00 00 04 fc fc fc fc 00 00 00 fc fc fc fc fc
                            ^
 ffff0000d0cf8a00: 00 00 00 00 fc fc fc fc 00 00 00 00 fc fc fc fc
 ffff0000d0cf8a80: fa fb fb fb fc fc fc fc 00 00 00 fc fc fc fc fc
==================================================================


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