Message-ID: <68ac6a46.a70a0220.303e5.0004.GAE@google.com>
Date: Mon, 25 Aug 2025 06:51:02 -0700
From: syzbot <syzbot+881d65229ca4f9ae8c84@...kaller.appspotmail.com>
To: hdanton@...a.com, linux-kernel@...r.kernel.org, 
	syzkaller-bugs@...glegroups.com
Subject: Re: [syzbot] [net?] unregister_netdevice: waiting for DEV to become
 free (8)

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
KASAN: use-after-free Read in j1939_netdev_stop

==================================================================
BUG: KASAN: use-after-free in read_pnet include/net/net_namespace.h:409 [inline]
BUG: KASAN: use-after-free in dev_net include/linux/netdevice.h:2718 [inline]
BUG: KASAN: use-after-free in j1939_can_rx_unregister net/can/j1939/main.c:202 [inline]
BUG: KASAN: use-after-free in __j1939_rx_release net/can/j1939/main.c:218 [inline]
BUG: KASAN: use-after-free in kref_put_mutex include/linux/kref.h:86 [inline]
BUG: KASAN: use-after-free in j1939_netdev_stop+0x2ab/0x2d0 net/can/j1939/main.c:311
Read of size 8 at addr ffff888023f80108 by task syz.0.17/6524

CPU: 0 UID: 0 PID: 6524 Comm: syz.0.17 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/12/2025
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
 read_pnet include/net/net_namespace.h:409 [inline]
 dev_net include/linux/netdevice.h:2718 [inline]
 j1939_can_rx_unregister net/can/j1939/main.c:202 [inline]
 __j1939_rx_release net/can/j1939/main.c:218 [inline]
 kref_put_mutex include/linux/kref.h:86 [inline]
 j1939_netdev_stop+0x2ab/0x2d0 net/can/j1939/main.c:311
 j1939_sk_release+0x5c3/0x8e0 net/can/j1939/socket.c:651
 __sock_release+0xb3/0x270 net/socket.c:649
 sock_close+0x1c/0x30 net/socket.c:1439
 __fput+0x402/0xb70 fs/file_table.c:468
 task_work_run+0x14d/0x240 kernel/task_work.c:227
 exit_task_work include/linux/task_work.h:40 [inline]
 do_exit+0x86f/0x2bf0 kernel/exit.c:961
 do_group_exit+0xd3/0x2a0 kernel/exit.c:1102
 get_signal+0x2673/0x26d0 kernel/signal.c:3034
 arch_do_signal_or_restart+0x8f/0x7d0 arch/x86/kernel/signal.c:337
 exit_to_user_mode_loop+0x84/0x110 kernel/entry/common.c:40
 exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline]
 syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline]
 do_syscall_64+0x3f6/0x4c0 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f408338ebe9
Code: Unable to access opcode bytes at 0x7f408338ebbf.
RSP: 002b:00007f4084235038 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: 0000000000000024 RBX: 00007f40835b5fa0 RCX: 00007f408338ebe9
RDX: 0000000000000000 RSI: 0000200000000200 RDI: 0000000000000003
RBP: 00007f4083411e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f40835b6038 R14: 00007f40835b5fa0 R15: 00007ffd085a2ed8
 </TASK>

The buggy address belongs to the physical page:
page: refcount:0 mapcount:0 mapping:0000000000000000 index:0xffff888023f80000 pfn:0x23f80
flags: 0xfff00000000000(node=0|zone=1|lastcpupid=0x7ff)
raw: 00fff00000000000 ffffea000174f608 ffffea0000c2c208 0000000000000000
raw: ffff888023f80000 0000000000000000 00000000ffffffff 0000000000000000
page dumped because: kasan: bad access detected
page_owner tracks the page as freed
page last allocated via order 3, migratetype Unmovable, gfp_mask 0x446dc0(GFP_KERNEL_ACCOUNT|__GFP_ZERO|__GFP_NOWARN|__GFP_RETRY_MAYFAIL|__GFP_COMP), pid 6440, tgid 6440 (syz-executor), ts 122667010586, free_ts 125938931446
 set_page_owner include/linux/page_owner.h:32 [inline]
 post_alloc_hook+0x1c0/0x230 mm/page_alloc.c:1851
 prep_new_page mm/page_alloc.c:1859 [inline]
 get_page_from_freelist+0x132b/0x38e0 mm/page_alloc.c:3858
 __alloc_frozen_pages_noprof+0x261/0x23f0 mm/page_alloc.c:5148
 alloc_pages_mpol+0x1fb/0x550 mm/mempolicy.c:2416
 ___kmalloc_large_node+0xed/0x160 mm/slub.c:4306
 __kmalloc_large_node_noprof+0x1c/0x70 mm/slub.c:4337
 __do_kmalloc_node mm/slub.c:4353 [inline]
 __kvmalloc_node_noprof.cold+0xb/0x65 mm/slub.c:5052
 alloc_netdev_mqs+0xd2/0x1530 net/core/dev.c:11812
 rtnl_create_link+0xc08/0xf90 net/core/rtnetlink.c:3633
 vxcan_newlink+0x2f8/0x640 drivers/net/can/vxcan.c:208
 rtnl_newlink_create net/core/rtnetlink.c:3825 [inline]
 __rtnl_newlink net/core/rtnetlink.c:3942 [inline]
 rtnl_newlink+0xc45/0x2000 net/core/rtnetlink.c:4057
 rtnetlink_rcv_msg+0x95e/0xe90 net/core/rtnetlink.c:6946
 netlink_rcv_skb+0x158/0x420 net/netlink/af_netlink.c:2552
 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
 netlink_unicast+0x5a7/0x870 net/netlink/af_netlink.c:1346
 netlink_sendmsg+0x8d1/0xdd0 net/netlink/af_netlink.c:1896
 sock_sendmsg_nosec net/socket.c:714 [inline]
 __sock_sendmsg net/socket.c:729 [inline]
 __sys_sendto+0x4a3/0x520 net/socket.c:2228
page last free pid 6524 tgid 6523 stack trace:
 reset_page_owner include/linux/page_owner.h:25 [inline]
 free_pages_prepare mm/page_alloc.c:1395 [inline]
 __free_frozen_pages+0x7d5/0x10f0 mm/page_alloc.c:2895
 device_release+0xa1/0x240 drivers/base/core.c:2565
 kobject_cleanup lib/kobject.c:689 [inline]
 kobject_release lib/kobject.c:720 [inline]
 kref_put include/linux/kref.h:65 [inline]
 kobject_put+0x1e7/0x5a0 lib/kobject.c:737
 netdev_run_todo+0x7e9/0x1320 net/core/dev.c:11513
 rtnl_unlock net/core/rtnetlink.c:157 [inline]
 rtnl_net_unlock include/linux/rtnetlink.h:135 [inline]
 rtnl_dellink+0x3da/0xa80 net/core/rtnetlink.c:3563
 rtnetlink_rcv_msg+0x95e/0xe90 net/core/rtnetlink.c:6946
 netlink_rcv_skb+0x158/0x420 net/netlink/af_netlink.c:2552
 netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
 netlink_unicast+0x5a7/0x870 net/netlink/af_netlink.c:1346
 netlink_sendmsg+0x8d1/0xdd0 net/netlink/af_netlink.c:1896
 sock_sendmsg_nosec net/socket.c:714 [inline]
 __sock_sendmsg net/socket.c:729 [inline]
 ____sys_sendmsg+0xa95/0xc70 net/socket.c:2614
 ___sys_sendmsg+0x134/0x1d0 net/socket.c:2668
 __sys_sendmsg+0x16d/0x220 net/socket.c:2700
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0xcd/0x4c0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Memory state around the buggy address:
 ffff888023f80000: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888023f80080: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
>ffff888023f80100: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
                      ^
 ffff888023f80180: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
 ffff888023f80200: ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff ff
==================================================================


Tested on:

commit:         1b237f19 Linux 6.17-rc3
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10b66862580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=d4703ac89d9e185a
dashboard link: https://syzkaller.appspot.com/bug?extid=881d65229ca4f9ae8c84
compiler:       gcc (Debian 12.2.0-14+deb12u1) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40
patch:          https://syzkaller.appspot.com/x/patch.diff?x=1417b862580000

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