[syzbot] [hams?] KASAN: slab-use-after-free Read in ax25_find_cb

[syzbot] [hams?] KASAN: slab-use-after-free Read in ax25_find_cb

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit:    250a17e8f955 Merge tag 'erofs-for-6.18-rc3-fixes' of git:/..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=154a3734580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d1ce99afe6f71855
dashboard link: https://syzkaller.appspot.com/bug?extid=caa052a0958a9146870d
compiler:       gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f51301069523/disk-250a17e8.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/a4671c3f2507/vmlinux-250a17e8.xz
kernel image: https://storage.googleapis.com/syzbot-assets/2b5a3b36a321/bzImage-250a17e8.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+caa052a0958a9146870d@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-use-after-free in ax25_find_cb+0x3b8/0x3f0 net/ax25/af_ax25.c:237
Read of size 1 at addr ffff888059c704c0 by task syz.6.2733/17200

CPU: 1 UID: 0 PID: 17200 Comm: syz.6.2733 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120
 print_address_description mm/kasan/report.c:378 [inline]
 print_report+0xcd/0x630 mm/kasan/report.c:482
 kasan_report+0xe0/0x110 mm/kasan/report.c:595
 ax25_find_cb+0x3b8/0x3f0 net/ax25/af_ax25.c:237
 ax25_send_frame+0x157/0xb60 net/ax25/ax25_out.c:55
 rose_send_frame+0xcc/0x2c0 net/rose/rose_link.c:106
 rose_transmit_restart_request+0x1b8/0x240 net/rose/rose_link.c:198
 rose_t0timer_expiry+0x1d/0x150 net/rose/rose_link.c:83
 call_timer_fn+0x19a/0x620 kernel/time/timer.c:1747
 expire_timers kernel/time/timer.c:1798 [inline]
 __run_timers+0x6ef/0x960 kernel/time/timer.c:2372
 __run_timer_base kernel/time/timer.c:2384 [inline]
 __run_timer_base kernel/time/timer.c:2376 [inline]
 run_timer_base+0x114/0x190 kernel/time/timer.c:2393
 run_timer_softirq+0x1a/0x40 kernel/time/timer.c:2403
 handle_softirqs+0x219/0x8e0 kernel/softirq.c:622
 __do_softirq kernel/softirq.c:656 [inline]
 invoke_softirq kernel/softirq.c:496 [inline]
 __irq_exit_rcu+0x109/0x170 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+0x57/0xc0 arch/x86/kernel/apic/apic.c:1052
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
RIP: 0033:0x7fd4a4c68253
Code: 1f 84 00 00 00 00 00 48 8b 70 f8 48 83 e8 08 48 39 f2 72 f3 48 39 c3 73 3e 48 89 33 48 83 c3 08 48 8b 70 f8 48 89 08 48 8b 0b <49> 8b 14 24 eb bf 48 39 f2 72 97 48 39 f0 73 46 49 89 34 24 48 89
RSP: 002b:00007ffd914df840 EFLAGS: 00000212
RAX: 00007fd4a4777648 RBX: 00007fd4a47774b0 RCX: ffffffff8a01d69a
RDX: ffffffff8a01d69a RSI: ffffffff8a01d69a RDI: 00007fd4a47777a0
RBP: 00007fd4a4777358 R08: 00007fd4a4777578 R09: 00007fd4a4fd2000
R10: 00007fd4a43fd008 R11: 000000000000000a R12: 00007fd4a4777350
R13: 0000000000000016 R14: 00007ffd914dfab8 R15: 00007fd4a43fd008
 </TASK>

Allocated by task 13773:
 kasan_save_stack+0x33/0x60 mm/kasan/common.c:56
 kasan_save_track+0x14/0x30 mm/kasan/common.c:77
 poison_kmalloc_redzone mm/kasan/common.c:400 [inline]
 __kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:417
 kmalloc_noprof include/linux/slab.h:957 [inline]
 rose_add_node net/rose/rose_route.c:109 [inline]
 rose_rt_ioctl+0x1c40/0x2580 net/rose/rose_route.c:748
 rose_ioctl+0x64d/0x7c0 net/rose/af_rose.c:1381
 sock_do_ioctl+0x118/0x280 net/socket.c:1254
 sock_ioctl+0x227/0x6b0 net/socket.c:1375
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl fs/ioctl.c:583 [inline]
 __x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0xfa0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 17183:
 kasan_save_stack+0x33/0x60 mm/kasan/common.c:56
 kasan_save_track+0x14/0x30 mm/kasan/common.c:77
 __kasan_save_free_info+0x3b/0x60 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+0x5f/0x80 mm/kasan/common.c:284
 kasan_slab_free include/linux/kasan.h:234 [inline]
 slab_free_hook mm/slub.c:2530 [inline]
 slab_free mm/slub.c:6619 [inline]
 kfree+0x2b8/0x6d0 mm/slub.c:6826
 rose_neigh_put include/net/rose.h:165 [inline]
 rose_timer_expiry+0x537/0x630 net/rose/rose_timer.c:183
 call_timer_fn+0x19a/0x620 kernel/time/timer.c:1747
 expire_timers kernel/time/timer.c:1798 [inline]
 __run_timers+0x6ef/0x960 kernel/time/timer.c:2372
 __run_timer_base kernel/time/timer.c:2384 [inline]
 __run_timer_base kernel/time/timer.c:2376 [inline]
 run_timer_base+0x114/0x190 kernel/time/timer.c:2393
 run_timer_softirq+0x1a/0x40 kernel/time/timer.c:2403
 handle_softirqs+0x219/0x8e0 kernel/softirq.c:622
 __do_softirq kernel/softirq.c:656 [inline]
 invoke_softirq kernel/softirq.c:496 [inline]
 __irq_exit_rcu+0x109/0x170 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+0xa4/0xc0 arch/x86/kernel/apic/apic.c:1052
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697

The buggy address belongs to the object at ffff888059c70480
 which belongs to the cache kmalloc-96 of size 96
The buggy address is located 64 bytes inside of
 freed 96-byte region [ffff888059c70480, ffff888059c704e0)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff888059c70b00 pfn:0x59c70
flags: 0xfff00000000200(workingset|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000200 ffff88813ffa6280 ffffea0001df33d0 ffffea0000c94410
raw: ffff888059c70b00 000000000020001f 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 5815, tgid 5815 (syz-executor), ts 66851059499, free_ts 66850862508
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x1c0/0x230 mm/page_alloc.c:1850
 prep_new_page mm/page_alloc.c:1858 [inline]
 get_page_from_freelist+0x10a3/0x3a30 mm/page_alloc.c:3884
 __alloc_frozen_pages_noprof+0x25f/0x2470 mm/page_alloc.c:5183
 alloc_pages_mpol+0x1fb/0x550 mm/mempolicy.c:2416
 alloc_slab_page mm/slub.c:3046 [inline]
 allocate_slab mm/slub.c:3219 [inline]
 new_slab+0x24a/0x360 mm/slub.c:3273
 ___slab_alloc+0xdc4/0x1ae0 mm/slub.c:4643
 __slab_alloc.constprop.0+0x63/0x110 mm/slub.c:4762
 __slab_alloc_node mm/slub.c:4838 [inline]
 slab_alloc_node mm/slub.c:5260 [inline]
 __kmalloc_cache_noprof+0x477/0x780 mm/slub.c:5750
 kmalloc_noprof include/linux/slab.h:957 [inline]
 kzalloc_noprof include/linux/slab.h:1094 [inline]
 class_dir_create_and_add drivers/base/core.c:3223 [inline]
 get_device_parent+0x2b1/0x4e0 drivers/base/core.c:3283
 device_add+0x1ad/0x1aa0 drivers/base/core.c:3613
 netdev_register_kobject+0x1a9/0x3d0 net/core/net-sysfs.c:2358
 register_netdevice+0x13dc/0x2270 net/core/dev.c:11294
 cfg80211_register_netdevice+0x149/0x340 net/wireless/core.c:1518
 ieee80211_if_add+0xc9d/0x1a40 net/mac80211/iface.c:2295
 ieee80211_register_hw+0x393b/0x4120 net/mac80211/main.c:1608
 mac80211_hwsim_new_radio+0x32d8/0x50b0 drivers/net/wireless/virtual/mac80211_hwsim.c:5803
page last free pid 5815 tgid 5815 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1394 [inline]
 __free_frozen_pages+0x7df/0x1160 mm/page_alloc.c:2906
 selinux_genfs_get_sid security/selinux/hooks.c:1357 [inline]
 inode_doinit_with_dentry+0xacb/0x12e0 security/selinux/hooks.c:1555
 selinux_d_instantiate+0x26/0x30 security/selinux/hooks.c:6523
 security_d_instantiate+0x142/0x1a0 security/security.c:4148
 d_instantiate+0x5c/0x90 fs/dcache.c:1961
 __debugfs_create_file+0x286/0x6b0 fs/debugfs/inode.c:459
 debugfs_create_file_short+0x41/0x60 fs/debugfs/inode.c:480
 add_link_files+0xff/0x120 net/mac80211/debugfs_netdev.c:990
 ieee80211_debugfs_add_netdev net/mac80211/debugfs_netdev.c:1011 [inline]
 ieee80211_debugfs_recreate_netdev+0xf70/0x17e0 net/mac80211/debugfs_netdev.c:1033
 ieee80211_if_add+0x9b9/0x1a40 net/mac80211/iface.c:2269
 ieee80211_register_hw+0x393b/0x4120 net/mac80211/main.c:1608
 mac80211_hwsim_new_radio+0x32d8/0x50b0 drivers/net/wireless/virtual/mac80211_hwsim.c:5803
 hwsim_new_radio_nl+0xba2/0x1330 drivers/net/wireless/virtual/mac80211_hwsim.c:6497
 genl_family_rcv_msg_doit+0x209/0x2f0 net/netlink/genetlink.c:1115
 genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline]
 genl_rcv_msg+0x55c/0x800 net/netlink/genetlink.c:1210
 netlink_rcv_skb+0x158/0x420 net/netlink/af_netlink.c:2552

Memory state around the buggy address:
 ffff888059c70380: 00 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc
 ffff888059c70400: 00 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc
>ffff888059c70480: fa fb fb fb fb fb fb fb fb fb fb fb fc fc fc fc
                                           ^
 ffff888059c70500: 00 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc
 ffff888059c70580: 00 00 00 00 00 00 00 00 00 fc fc fc fc fc fc fc
==================================================================


---
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[PATCH] net: rose: Prevent the use of freed digipeat

[Lizhi Xu]

There is no synchronization between the two timers, rose_t0timer_expiry
and rose_timer_expiry.
rose_timer_expiry() puts the neighbor when the rose state is ROSE_STATE_2.
However, rose_t0timer_expiry() does initiate a restart request on the
neighbor.
When rose_t0timer_expiry() accesses the released neighbor member digipeat,
a UAF is triggered.

To avoid this uaf, when rose_timer_expiry() puts the neighbor, the base
member digipeat is set to NULL.

syzbot reported a slab-use-after-free Read in ax25_find_cb.
BUG: KASAN: slab-use-after-free in ax25_find_cb+0x3b8/0x3f0 net/ax25/af_ax25.c:237
Read of size 1 at addr ffff888059c704c0 by task syz.6.2733/17200

Call Trace:
 ax25_find_cb+0x3b8/0x3f0 net/ax25/af_ax25.c:237
 ax25_send_frame+0x157/0xb60 net/ax25/ax25_out.c:55
 rose_send_frame+0xcc/0x2c0 net/rose/rose_link.c:106
 rose_transmit_restart_request+0x1b8/0x240 net/rose/rose_link.c:198
 rose_t0timer_expiry+0x1d/0x150 net/rose/rose_link.c:83

Freed by task 17183:
 kfree+0x2b8/0x6d0 mm/slub.c:6826
 rose_neigh_put include/net/rose.h:165 [inline]
 rose_timer_expiry+0x537/0x630 net/rose/rose_timer.c:183
 call_timer_fn+0x19a/0x620 kernel/time/timer.c:1747

Fixes: dcb34659028f ("net: rose: split remove and free operations in rose_remove_neigh()")
Reported-by: syzbot+caa052a0958a9146870d@syzkaller.appspotmail.com
Signed-off-by: Lizhi Xu <lizhi.xu@windriver.com>
---
 include/net/rose.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/include/net/rose.h b/include/net/rose.h
index 2b5491bbf39a..9b0dc81a9589 100644
--- a/include/net/rose.h
+++ b/include/net/rose.h
@@ -163,6 +163,7 @@ static inline void rose_neigh_put(struct rose_neigh *rose_neigh)
 		if (rose_neigh->ax25)
 			ax25_cb_put(rose_neigh->ax25);
 		kfree(rose_neigh->digipeat);
+		rose_neigh->digipeat = NULL;
 		kfree(rose_neigh);
 	}
 }
-- 
2.43.0

Re: [PATCH] net: rose: Prevent the use of freed digipeat

[Kuniyuki Iwashima]

From: Lizhi Xu <lizhi.xu@windriver.com>
Date: Fri, 24 Oct 2025 09:31:53 +0800
> There is no synchronization between the two timers, rose_t0timer_expiry
> and rose_timer_expiry.
> rose_timer_expiry() puts the neighbor when the rose state is ROSE_STATE_2.
> However, rose_t0timer_expiry() does initiate a restart request on the
> neighbor.
> When rose_t0timer_expiry() accesses the released neighbor member digipeat,
> a UAF is triggered.
> 
> To avoid this uaf, when rose_timer_expiry() puts the neighbor, the base
> member digipeat is set to NULL.
> 
> syzbot reported a slab-use-after-free Read in ax25_find_cb.
> BUG: KASAN: slab-use-after-free in ax25_find_cb+0x3b8/0x3f0 net/ax25/af_ax25.c:237
> Read of size 1 at addr ffff888059c704c0 by task syz.6.2733/17200
> 
> Call Trace:
>  ax25_find_cb+0x3b8/0x3f0 net/ax25/af_ax25.c:237
>  ax25_send_frame+0x157/0xb60 net/ax25/ax25_out.c:55
>  rose_send_frame+0xcc/0x2c0 net/rose/rose_link.c:106
>  rose_transmit_restart_request+0x1b8/0x240 net/rose/rose_link.c:198
>  rose_t0timer_expiry+0x1d/0x150 net/rose/rose_link.c:83
> 
> Freed by task 17183:
>  kfree+0x2b8/0x6d0 mm/slub.c:6826
>  rose_neigh_put include/net/rose.h:165 [inline]
>  rose_timer_expiry+0x537/0x630 net/rose/rose_timer.c:183
>  call_timer_fn+0x19a/0x620 kernel/time/timer.c:1747
> 
> Fixes: dcb34659028f ("net: rose: split remove and free operations in rose_remove_neigh()")
> Reported-by: syzbot+caa052a0958a9146870d@syzkaller.appspotmail.com
> Signed-off-by: Lizhi Xu <lizhi.xu@windriver.com>
> ---
>  include/net/rose.h | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/include/net/rose.h b/include/net/rose.h
> index 2b5491bbf39a..9b0dc81a9589 100644
> --- a/include/net/rose.h
> +++ b/include/net/rose.h
> @@ -163,6 +163,7 @@ static inline void rose_neigh_put(struct rose_neigh *rose_neigh)
>  		if (rose_neigh->ax25)
>  			ax25_cb_put(rose_neigh->ax25);
>  		kfree(rose_neigh->digipeat);
> +		rose_neigh->digipeat = NULL;

How does this synchronise with the timer which is going to
touch rose_neigh being freed below ?


>  		kfree(rose_neigh);

Isn't the problem that we reach here without stopping all timers
or that a timer does not hold refcnt ?


Also, please post a patch in a separate thread so that patchwork
will not be confused.

https://www.kernel.org/doc/html/latest/process/maintainer-netdev.html#resending-after-review

---8<---
The new version of patches should be posted as a separate
thread, not as a reply to the previous posting.
---8<---

[PATCH] net: rose: Prevent the use of freed digipeat

[Lizhi Xu]

There is no synchronization between the two timers, rose_t0timer_expiry
and rose_timer_expiry.
rose_timer_expiry() puts the neighbor when the rose state is ROSE_STATE_2.
However, rose_t0timer_expiry() does initiate a restart request on the
neighbor.
When rose_t0timer_expiry() accesses the released neighbor member digipeat,
a UAF is triggered.

To avoid this UAF, defer the put operation to rose_t0timer_expiry() and
stop restarting t0timer after putting the neighbor.

When putting the neighbor, set the neighbor to NULL. Setting neighbor to
NULL prevents rose_t0timer_expiry() from restarting t0timer.

syzbot reported a slab-use-after-free Read in ax25_find_cb.
BUG: KASAN: slab-use-after-free in ax25_find_cb+0x3b8/0x3f0 net/ax25/af_ax25.c:237
Read of size 1 at addr ffff888059c704c0 by task syz.6.2733/17200
Call Trace:
 ax25_find_cb+0x3b8/0x3f0 net/ax25/af_ax25.c:237
 ax25_send_frame+0x157/0xb60 net/ax25/ax25_out.c:55
 rose_send_frame+0xcc/0x2c0 net/rose/rose_link.c:106
 rose_transmit_restart_request+0x1b8/0x240 net/rose/rose_link.c:198
 rose_t0timer_expiry+0x1d/0x150 net/rose/rose_link.c:83

Freed by task 17183:
 kfree+0x2b8/0x6d0 mm/slub.c:6826
 rose_neigh_put include/net/rose.h:165 [inline]
 rose_timer_expiry+0x537/0x630 net/rose/rose_timer.c:183

Fixes: d860d1faa6b2 ("net: rose: convert 'use' field to refcount_t")
Reported-by: syzbot+caa052a0958a9146870d@syzkaller.appspotmail.com
Signed-off-by: Lizhi Xu <lizhi.xu@windriver.com>
---
V1 -> V2: Putting the neighbor stops t0timer from automatically starting

 include/net/rose.h   | 1 +
 net/rose/rose_link.c | 5 +++++
 2 files changed, 6 insertions(+)

diff --git a/include/net/rose.h b/include/net/rose.h
index 2b5491bbf39a..ecf37c8e24bb 100644
--- a/include/net/rose.h
+++ b/include/net/rose.h
@@ -164,6 +164,7 @@ static inline void rose_neigh_put(struct rose_neigh *rose_neigh)
 			ax25_cb_put(rose_neigh->ax25);
 		kfree(rose_neigh->digipeat);
 		kfree(rose_neigh);
+		rose_neigh = NULL;
 	}
 }
 
diff --git a/net/rose/rose_link.c b/net/rose/rose_link.c
index 7746229fdc8c..524e7935bd02 100644
--- a/net/rose/rose_link.c
+++ b/net/rose/rose_link.c
@@ -43,6 +43,9 @@ void rose_start_ftimer(struct rose_neigh *neigh)
 
 static void rose_start_t0timer(struct rose_neigh *neigh)
 {
+	if (!neigh)
+		return;
+
 	timer_delete(&neigh->t0timer);
 
 	neigh->t0timer.function = rose_t0timer_expiry;
@@ -80,10 +83,12 @@ static void rose_t0timer_expiry(struct timer_list *t)
 {
 	struct rose_neigh *neigh = timer_container_of(neigh, t, t0timer);
 
+	rose_neigh_hold(neigh);
 	rose_transmit_restart_request(neigh);
 
 	neigh->dce_mode = 0;
 
+	rose_neigh_put(neigh);
 	rose_start_t0timer(neigh);
 }
 
-- 
2.43.0

Re: [PATCH] net: rose: Prevent the use of freed digipeat

[Jakub Kicinski]

On Fri, 24 Oct 2025 17:05:21 +0800 Lizhi Xu wrote:
> There is no synchronization between the two timers, rose_t0timer_expiry
> and rose_timer_expiry.
> rose_timer_expiry() puts the neighbor when the rose state is ROSE_STATE_2.
> However, rose_t0timer_expiry() does initiate a restart request on the
> neighbor.

Read what reviewers tell you please.

Kuniyuki already told you not to send patches in reply to existing
threads.

Re: [syzbot] [hams?] KASAN: slab-use-after-free Read in ax25_find_cb

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit:    c75caf76ed86 Add linux-next specific files for 20251209
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=14e91eb4580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=b9f785244b836412
dashboard link: https://syzkaller.appspot.com/bug?extid=caa052a0958a9146870d
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=15b62a1a580000
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=144caec2580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/5262ac64cf0f/disk-c75caf76.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ef5f82dd5e01/vmlinux-c75caf76.xz
kernel image: https://storage.googleapis.com/syzbot-assets/1e93d794f3bf/bzImage-c75caf76.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+caa052a0958a9146870d@syzkaller.appspotmail.com

==================================================================
BUG: KASAN: slab-use-after-free in ax25_find_cb+0x179/0x3a0 net/ax25/af_ax25.c:236
Read of size 8 at addr ffff888077f9da10 by task syz.2.252/6544

CPU: 1 UID: 0 PID: 6544 Comm: syz.2.252 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
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
 ax25_find_cb+0x179/0x3a0 net/ax25/af_ax25.c:236
 rose_link_up net/rose/rose_link.c:129 [inline]
 rose_transmit_link+0x16d/0x740 net/rose/rose_link.c:271
 rose_write_internal+0x11dc/0x1ac0 net/rose/rose_subr.c:198
 rose_connect+0x909/0x10a0 net/rose/af_rose.c:881
 __sys_connect_file net/socket.c:2104 [inline]
 __sys_connect+0x316/0x440 net/socket.c:2123
 __do_sys_connect net/socket.c:2129 [inline]
 __se_sys_connect net/socket.c:2126 [inline]
 __x64_sys_connect+0x7a/0x90 net/socket.c:2126
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f98cf98f749
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:00007f98d08e5038 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: 00007f98cfbe5fa0 RCX: 00007f98cf98f749
RDX: 0000000000000040 RSI: 0000200000000100 RDI: 0000000000000005
RBP: 00007f98cfa13f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f98cfbe6038 R14: 00007f98cfbe5fa0 R15: 00007fff4c13b338
 </TASK>

Allocated by task 6474:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 poison_kmalloc_redzone mm/kasan/common.c:398 [inline]
 __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415
 kasan_kmalloc include/linux/kasan.h:262 [inline]
 __kmalloc_cache_noprof+0x3e2/0x700 mm/slub.c:5776
 kmalloc_noprof include/linux/slab.h:957 [inline]
 kzalloc_noprof include/linux/slab.h:1094 [inline]
 ax25_dev_device_up+0x54/0x600 net/ax25/ax25_dev.c:57
 ax25_device_event+0x124/0x630 net/ax25/af_ax25.c:143
 notifier_call_chain+0x19d/0x3a0 kernel/notifier.c:85
 call_netdevice_notifiers_extack net/core/dev.c:2269 [inline]
 call_netdevice_notifiers net/core/dev.c:2283 [inline]
 __dev_notify_flags+0x18d/0x2e0 net/core/dev.c:-1
 netif_change_flags+0xe8/0x1a0 net/core/dev.c:9803
 dev_change_flags+0x130/0x260 net/core/dev_api.c:68
 dev_ioctl+0x7b4/0x1150 net/core/dev_ioctl.c:842
 sock_do_ioctl+0x22c/0x300 net/socket.c:1283
 sock_ioctl+0x576/0x790 net/socket.c:1390
 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/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Freed by task 37:
 kasan_save_stack mm/kasan/common.c:57 [inline]
 kasan_save_track+0x3e/0x80 mm/kasan/common.c:78
 kasan_save_free_info+0x46/0x50 mm/kasan/generic.c:584
 poison_slab_object mm/kasan/common.c:253 [inline]
 __kasan_slab_free+0x5c/0x80 mm/kasan/common.c:285
 kasan_slab_free include/linux/kasan.h:234 [inline]
 slab_free_hook mm/slub.c:2540 [inline]
 slab_free_freelist_hook mm/slub.c:2569 [inline]
 slab_free_bulk mm/slub.c:6701 [inline]
 kmem_cache_free_bulk+0x3fb/0xdb0 mm/slub.c:7388
 kfree_bulk include/linux/slab.h:830 [inline]
 kvfree_rcu_bulk+0xe5/0x1f0 mm/slab_common.c:1523
 kfree_rcu_work+0xed/0x170 mm/slab_common.c:1601
 process_one_work+0x93a/0x15a0 kernel/workqueue.c:3279
 process_scheduled_works kernel/workqueue.c:3362 [inline]
 worker_thread+0x9b0/0xee0 kernel/workqueue.c:3443
 kthread+0x711/0x8a0 kernel/kthread.c:463
 ret_from_fork+0x599/0xb30 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246

Last potentially related work creation:
 kasan_save_stack+0x3e/0x60 mm/kasan/common.c:57
 kasan_record_aux_stack+0xbd/0xd0 mm/kasan/generic.c:556
 kvfree_call_rcu+0x11b/0x480 mm/slab_common.c:1994
 ax25_device_event+0x57e/0x630 net/ax25/af_ax25.c:148
 notifier_call_chain+0x19d/0x3a0 kernel/notifier.c:85
 call_netdevice_notifiers_extack net/core/dev.c:2269 [inline]
 call_netdevice_notifiers net/core/dev.c:2283 [inline]
 __dev_notify_flags+0x18d/0x2e0 net/core/dev.c:-1
 netif_change_flags+0xe8/0x1a0 net/core/dev.c:9803
 dev_change_flags+0x130/0x260 net/core/dev_api.c:68
 dev_ioctl+0x7b4/0x1150 net/core/dev_ioctl.c:842
 sock_do_ioctl+0x22c/0x300 net/socket.c:1283
 sock_ioctl+0x576/0x790 net/socket.c:1390
 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/0xf80 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

The buggy address belongs to the object at ffff888077f9da00
 which belongs to the cache kmalloc-256 of size 256
The buggy address is located 16 bytes inside of
 freed 256-byte region [ffff888077f9da00, ffff888077f9db00)

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x77f9c
head: order:1 mapcount:0 entire_mapcount:0 nr_pages_mapped:0 pincount:0
anon flags: 0xfff00000000040(head|node=0|zone=1|lastcpupid=0x7ff)
page_type: f5(slab)
raw: 00fff00000000040 ffff88813fe26b40 0000000000000000 dead000000000001
raw: 0000000000000000 0000000000100010 00000000f5000000 0000000000000000
head: 00fff00000000040 ffff88813fe26b40 0000000000000000 dead000000000001
head: 0000000000000000 0000000000100010 00000000f5000000 0000000000000000
head: 00fff00000000001 ffffea0001dfe701 00000000ffffffff 00000000ffffffff
head: ffffffffffffffff 0000000000000000 00000000ffffffff 0000000000000002
page dumped because: kasan: bad access detected
page_owner tracks the page as allocated
page last allocated via order 1, migratetype Unmovable, gfp_mask 0x252800(GFP_NOWAIT|__GFP_NORETRY|__GFP_COMP|__GFP_THISNODE), pid 5886, tgid 5886 (syz-executor), ts 158848081003, free_ts 158761437861
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x234/0x290 mm/page_alloc.c:1846
 prep_new_page mm/page_alloc.c:1854 [inline]
 get_page_from_freelist+0x2365/0x2440 mm/page_alloc.c:3915
 __alloc_frozen_pages_noprof+0x181/0x370 mm/page_alloc.c:5210
 alloc_slab_page mm/slub.c:3077 [inline]
 allocate_slab+0x7a/0x3b0 mm/slub.c:3248
 new_slab mm/slub.c:3302 [inline]
 ___slab_alloc+0xf2b/0x1960 mm/slub.c:4656
 __slab_alloc+0x65/0x100 mm/slub.c:4779
 __slab_alloc_node mm/slub.c:4855 [inline]
 slab_alloc_node mm/slub.c:5251 [inline]
 __do_kmalloc_node mm/slub.c:5656 [inline]
 __kmalloc_node_noprof+0x5d9/0x820 mm/slub.c:5663
 kmalloc_array_node_noprof include/linux/slab.h:1075 [inline]
 alloc_slab_obj_exts+0x3e/0x100 mm/slub.c:2123
 account_slab mm/slub.c:3202 [inline]
 allocate_slab+0x1cc/0x3b0 mm/slub.c:3267
 new_slab mm/slub.c:3302 [inline]
 ___slab_alloc+0xf2b/0x1960 mm/slub.c:4656
 __slab_alloc+0x65/0x100 mm/slub.c:4779
 __slab_alloc_node mm/slub.c:4855 [inline]
 slab_alloc_node mm/slub.c:5251 [inline]
 __do_kmalloc_node mm/slub.c:5656 [inline]
 __kvmalloc_node_noprof+0x6b6/0x920 mm/slub.c:7134
 allocate_hook_entries_size net/netfilter/core.c:58 [inline]
 nf_hook_entries_grow+0x281/0x720 net/netfilter/core.c:137
 __nf_register_net_hook+0x2c9/0x930 net/netfilter/core.c:432
 nf_register_net_hook+0xb2/0x190 net/netfilter/core.c:575
 nf_register_net_hooks+0x44/0x1b0 net/netfilter/core.c:591
page last free pid 5902 tgid 5902 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1395 [inline]
 __free_frozen_pages+0xbc8/0xd30 mm/page_alloc.c:2943
 discard_slab mm/slub.c:3346 [inline]
 __put_partials+0x146/0x170 mm/slub.c:3886
 put_cpu_partial+0x1f2/0x2d0 mm/slub.c:3961
 __slab_free+0x288/0x2a0 mm/slub.c:5952
 qlink_free mm/kasan/quarantine.c:163 [inline]
 qlist_free_all+0x97/0x100 mm/kasan/quarantine.c:179
 kasan_quarantine_reduce+0x148/0x160 mm/kasan/quarantine.c:286
 __kasan_slab_alloc+0x22/0x80 mm/kasan/common.c:350
 kasan_slab_alloc include/linux/kasan.h:252 [inline]
 slab_post_alloc_hook mm/slub.c:4953 [inline]
 slab_alloc_node mm/slub.c:5263 [inline]
 kmem_cache_alloc_lru_noprof+0x36c/0x6e0 mm/slub.c:5282
 __d_alloc+0x37/0x6f0 fs/dcache.c:1730
 d_alloc+0x4b/0x190 fs/dcache.c:1809
 lookup_one_qstr_excl+0xdc/0x360 fs/namei.c:1743
 __start_dirop fs/namei.c:2866 [inline]
 start_dirop+0x5c/0x90 fs/namei.c:2875
 simple_start_creating+0xc4/0x100 fs/libfs.c:2338
 debugfs_start_creating+0xdb/0x1a0 fs/debugfs/inode.c:394
 __debugfs_create_file+0x6f/0x400 fs/debugfs/inode.c:428
 debugfs_create_file_full+0x3f/0x60 fs/debugfs/inode.c:460

Memory state around the buggy address:
 ffff888077f9d900: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 ffff888077f9d980: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
>ffff888077f9da00: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
                         ^
 ffff888077f9da80: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 ffff888077f9db00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
==================================================================


---
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