KASAN: slab-out-of-bounds Read in __dynamic_pr_debug

Status: upstream: reported on 2026/09/16 06:54
Reported-by: syzbot+bf5d3c048e61b09c026e@syzkaller.appspotmail.com
First crash: 1d11h, last: 17h45m
▶ ▼ Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream KASAN: slab-out-of-bounds Read in __dynamic_pr_debug prio:high net nfc 17 syz, C 103 20m 29d 0/29 upstream: reported C repro on 2026/08/19 05:22
linux-5.15 KASAN: slab-out-of-bounds Read in __dynamic_pr_debug 17 6 14h36m 1d11h 0/3 upstream: reported on 2026/09/16 06:37

Sample crash report:
==================================================================
BUG: KASAN: slab-out-of-bounds in string_nocheck lib/vsprintf.c:645 [inline]
BUG: KASAN: slab-out-of-bounds in string+0x204/0x290 lib/vsprintf.c:727
Read of size 1 at addr ffff88807c1376e1 by task syz.4.847/8294

CPU: 1 PID: 8294 Comm: syz.4.847 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
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
 string_nocheck lib/vsprintf.c:645 [inline]
 string+0x204/0x290 lib/vsprintf.c:727
 vsnprintf+0xf72/0x1ba0 lib/vsprintf.c:2823
 va_format lib/vsprintf.c:1682 [inline]
 pointer+0x9ed/0x1150 lib/vsprintf.c:2454
 vsnprintf+0xdaa/0x1ba0 lib/vsprintf.c:2827
 vprintk_store+0x3d9/0xd50 kernel/printk/printk.c:2226
 vprintk_emit+0x117/0x610 kernel/printk/printk.c:2322
 _printk+0xde/0x130 kernel/printk/printk.c:2366
 __dynamic_pr_debug+0x1a3/0x260 lib/dynamic_debug.c:879
 nfc_llcp_wks_sap net/nfc/llcp_core.c:342 [inline]
 nfc_llcp_get_sdp_ssap+0x3a4/0x3d0 net/nfc/llcp_core.c:418
 llcp_sock_bind+0x3be/0x710 net/nfc/llcp_sock.c:114
 __sys_bind+0x2f0/0x3f0 net/socket.c:1856
 __do_sys_bind net/socket.c:1867 [inline]
 __se_sys_bind net/socket.c:1865 [inline]
 __x64_sys_bind+0x7a/0x90 net/socket.c:1865
 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: 0033:0x7f4b0eb9e159
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:00007f4b0fb19028 EFLAGS: 00000246 ORIG_RAX: 0000000000000031
RAX: ffffffffffffffda RBX: 00007f4b0ee25fa0 RCX: 00007f4b0eb9e159
RDX: 0000000000000060 RSI: 0000200000000080 RDI: 0000000000000004
RBP: 00007f4b0ec3506b R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f4b0ee26038 R14: 00007f4b0ee25fa0 R15: 00007ffeb8cfe2c8
 </TASK>

Allocated by task 8294:
 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
 kasan_kmalloc include/linux/kasan.h:198 [inline]
 __do_kmalloc_node mm/slab_common.c:1007 [inline]
 __kmalloc_node_track_caller+0xb4/0x230 mm/slab_common.c:1027
 kmemdup+0x2b/0x70 mm/util.c:131
 kmemdup include/linux/fortify-string.h:779 [inline]
 llcp_sock_bind+0x370/0x710 net/nfc/llcp_sock.c:107
 __sys_bind+0x2f0/0x3f0 net/socket.c:1856
 __do_sys_bind net/socket.c:1867 [inline]
 __se_sys_bind net/socket.c:1865 [inline]
 __x64_sys_bind+0x7a/0x90 net/socket.c:1865
 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 ffff88807c1376e0
 which belongs to the cache kmalloc-8 of size 8
The buggy address is located 0 bytes to the right of
 allocated 1-byte region [ffff88807c1376e0, ffff88807c1376e1)

The buggy address belongs to the physical page:
page:ffffea0001f04dc0 refcount:1 mapcount:0 mapping:0000000000000000 index:0xffff88807c137b40 pfn:0x7c137
anon flags: 0xfff00000000800(slab|node=0|zone=1|lastcpupid=0x7ff)
page_type: 0xffffffff()
raw: 00fff00000000800 ffff888017c41280 0000000000000000 0000000000000001
raw: ffff88807c137b40 0000000080660064 00000001ffffffff 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 0x112cc0(GFP_USER|__GFP_NOWARN|__GFP_NORETRY), pid 8102, tgid 8101 (syz.2.801), ts 168611170319, free_ts 167679994797
 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]
 kernfs_fop_write_iter+0x158/0x520 fs/kernfs/file.c:329
 call_write_iter include/linux/fs.h:2018 [inline]
 new_sync_write fs/read_write.c:491 [inline]
 vfs_write+0x474/0x9a0 fs/read_write.c:584
 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
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
 discard_slab mm/slub.c:2127 [inline]
 __unfreeze_partials+0x1cf/0x210 mm/slub.c:2667
 put_cpu_partial+0x17c/0x250 mm/slub.c:2743
 __slab_free+0x319/0x400 mm/slub.c:3700
 qlink_free mm/kasan/quarantine.c:166 [inline]
 qlist_free_all+0x75/0xd0 mm/kasan/quarantine.c:185
 kasan_quarantine_reduce+0x143/0x160 mm/kasan/quarantine.c:292
 __kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:306
 kasan_slab_alloc include/linux/kasan.h:188 [inline]
 slab_post_alloc_hook+0x6a/0x4d0 mm/slab.h:770
 slab_alloc_node mm/slub.c:3495 [inline]
 __kmem_cache_alloc_node+0x194/0x250 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]
 __register_sysctl_table+0x71/0x1210 fs/proc/proc_sysctl.c:1373
 neigh_sysctl_register+0x9db/0xac0 net/core/neighbour.c:3878
 addrconf_sysctl_register+0xac/0x1b0 net/ipv6/addrconf.c:7274
 ipv6_add_dev+0xc47/0x11f0 net/ipv6/addrconf.c:451
 addrconf_notify+0x67b/0x1010 net/ipv6/addrconf.c:3652

Memory state around the buggy address:
 ffff88807c137580: fc fc fc fc fb fc fc fc fc fb fc fc fc fc fb fc
 ffff88807c137600: fc fc fc fb fc fc fc fc fb fc fc fc fc fb fc fc
>ffff88807c137680: fc fc fb fc fc fc fc fb fc fc fc fc 01 fc fc fc
                                                       ^
 ffff88807c137700: fc fb fc fc fc fc fa fc fc fc fc 00 fc fc fc fc
 ffff88807c137780: fa fc fc fc fc fa fc fc fc fc fa fc fc fc fc fa
==================================================================

Crashes (3):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/17 00:12 linux-6.6.y 79643295eba1 95928915 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-out-of-bounds Read in __dynamic_pr_debug
2026/09/17 00:12 linux-6.6.y 79643295eba1 95928915 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-out-of-bounds Read in __dynamic_pr_debug
2026/09/16 06:53 linux-6.6.y 79643295eba1 12a0a44a .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan KASAN: slab-out-of-bounds Read in __dynamic_pr_debug
* Struck through repros no longer work on HEAD.