[syzbot] [hams?] KASAN: slab-use-after-free Read in nr_add_node

syzbot
2025-09-25T16:35:25Z

Hello,

syzbot found the following issue on:

HEAD commit: 846bd2225ec3 Add linux-next specific files for 20250919
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=130c08e2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=135377594f35b576
dashboard link: https://syzkaller.appspot.com/bug?extid=2860e75836a08b172755
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=13f3fe42580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/c53d48022f8a/disk-846bd222.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/483534e784c8/vmlinux-846bd222.xz
kernel image: https://storage.googleapis.com/syzbot-assets/721b36eec9b3/bzImage-846bd222.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+2860e75836a08b172755@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-use-after-free in nr_add_node+0x251b/0x2580 net/netrom/nr_route.c:248
Read of size 2 at addr ffff888078ae2632 by task syz.0.4719/15936

CPU: 0 UID: 0 PID: 15936 Comm: syz.0.4719 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
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/0x240 mm/kasan/report.c:482
kasan_report+0x118/0x150 mm/kasan/report.c:595
nr_add_node+0x251b/0x2580 net/netrom/nr_route.c:248
nr_rt_ioctl+0x9f1/0xb00 net/netrom/nr_route.c:651
sock_do_ioctl+0xdc/0x300 net/socket.c:1241
sock_ioctl+0x576/0x790 net/socket.c:1362
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f29de38ec29
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f29df216038 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f29de5d5fa0 RCX: 00007f29de38ec29
RDX: 0000200000000000 RSI: 000000000000890b RDI: 0000000000000004
RBP: 00007f29de411e41 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f29de5d6038 R14: 00007f29de5d5fa0 R15: 00007ffedaf2ceb8
</TASK>

Allocated by task 15939:
kasan_save_stack mm/kasan/common.c:56 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:77
poison_kmalloc_redzone mm/kasan/common.c:400 [inline]
__kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:417
kasan_kmalloc include/linux/kasan.h:262 [inline]
__kmalloc_cache_noprof+0x3d5/0x6f0 mm/slub.c:5723
kmalloc_noprof include/linux/slab.h:957 [inline]
nr_add_node+0x804/0x2580 net/netrom/nr_route.c:146
nr_rt_ioctl+0x9f1/0xb00 net/netrom/nr_route.c:651
sock_do_ioctl+0xdc/0x300 net/socket.c:1241
sock_ioctl+0x576/0x790 net/socket.c:1362
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 15936:
kasan_save_stack mm/kasan/common.c:56 [inline]
kasan_save_track+0x3e/0x80 mm/kasan/common.c:77
__kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:587
kasan_save_free_info mm/kasan/kasan.h:406 [inline]
poison_slab_object mm/kasan/common.c:252 [inline]
__kasan_slab_free+0x5c/0x80 mm/kasan/common.c:284
kasan_slab_free include/linux/kasan.h:234 [inline]
slab_free_hook mm/slub.c:2507 [inline]
slab_free mm/slub.c:6557 [inline]
kfree+0x19a/0x6d0 mm/slub.c:6765
nr_add_node+0x1cbe/0x2580 net/netrom/nr_route.c:246
nr_rt_ioctl+0x9f1/0xb00 net/netrom/nr_route.c:651
sock_do_ioctl+0xdc/0x300 net/socket.c:1241
sock_ioctl+0x576/0x790 net/socket.c:1362
vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:597 [inline]
__se_sys_ioctl+0xfc/0x170 fs/ioctl.c:583
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff888078ae2600
which belongs to the cache kmalloc-64 of size 64
The buggy address is located 50 bytes inside of
freed 64-byte region [ffff888078ae2600, ffff888078ae2640)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x78ae2
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000000 ffff88801b0418c0 ffffea0000c51900 dead000000000004
raw: 0000000000000000 0000000000200020 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 0x52c40(GFP_NOFS|__GFP_NOWARN|__GFP_NORETRY|__GFP_COMP), pid 5233, tgid 5233 (udevd), ts 92365645188, free_ts 92323224662
set_page_owner include/linux/page_owner.h:32 [inline]
post_alloc_hook+0x240/0x2a0 mm/page_alloc.c:1850
prep_new_page mm/page_alloc.c:1858 [inline]
get_page_from_freelist+0x21e4/0x22c0 mm/page_alloc.c:3869
__alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5159
alloc_pages_mpol+0x232/0x4a0 mm/mempolicy.c:2416
alloc_slab_page mm/slub.c:3023 [inline]
allocate_slab+0x96/0x3a0 mm/slub.c:3196
new_slab mm/slub.c:3250 [inline]
___slab_alloc+0xe94/0x1920 mm/slub.c:4626
__slab_alloc+0x65/0x100 mm/slub.c:4745
__slab_alloc_node mm/slub.c:4821 [inline]
slab_alloc_node mm/slub.c:5232 [inline]
__do_kmalloc_node mm/slub.c:5601 [inline]
__kmalloc_noprof+0x471/0x7f0 mm/slub.c:5614
kmalloc_noprof include/linux/slab.h:961 [inline]
kzalloc_noprof include/linux/slab.h:1094 [inline]
tomoyo_encode2 security/tomoyo/realpath.c:45 [inline]
tomoyo_encode+0x28b/0x550 security/tomoyo/realpath.c:80
tomoyo_realpath_from_path+0x58d/0x5d0 security/tomoyo/realpath.c:283
tomoyo_get_realpath security/tomoyo/file.c:151 [inline]
tomoyo_path_perm+0x213/0x4b0 security/tomoyo/file.c:822
security_inode_getattr+0x12f/0x330 security/security.c:2416
vfs_getattr fs/stat.c:259 [inline]
vfs_fstat fs/stat.c:281 [inline]
__do_sys_newfstat fs/stat.c:555 [inline]
__se_sys_newfstat fs/stat.c:550 [inline]
__x64_sys_newfstat+0xfc/0x200 fs/stat.c:550
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xfa0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
page last free pid 5528 tgid 5528 stack trace:
reset_page_owner include/linux/page_owner.h:25 [inline]
free_pages_prepare mm/page_alloc.c:1394 [inline]
__free_frozen_pages+0xbc4/0xd30 mm/page_alloc.c:2906
rcu_do_batch kernel/rcu/tree.c:2605 [inline]
rcu_core+0xcab/0x1770 kernel/rcu/tree.c:2861
handle_softirqs+0x286/0x870 kernel/softirq.c:622
__do_softirq kernel/softirq.c:656 [inline]
invoke_softirq kernel/softirq.c:496 [inline]
__irq_exit_rcu+0xca/0x1f0 kernel/softirq.c:723
irq_exit_rcu+0x9/0x30 kernel/softirq.c:739
instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1052 [inline]
sysvec_apic_timer_interrupt+0xa6/0xc0 arch/x86/kernel/apic/apic.c:1052
asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697

Memory state around the buggy address:
ffff888078ae2500: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
ffff888078ae2580: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
>ffff888078ae2600: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
^
ffff888078ae2680: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
ffff888078ae2700: fa fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
==================================================================

---
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