On 2/13/25 17:11, Ido Schimmel wrote:
> On Wed, Feb 12, 2025 at 01:41:51PM +0000, Gavrilov Ilia wrote:
>> Syzkaller reports the following bug:
>>
>> BUG: spinlock bad magic on CPU#1, syz-executor.0/7995
>> lock: 0xffff88805303f3e0, .magic: 00000000, .owner: <none>/-1, .owner_cpu: 0
>> CPU: 1 PID: 7995 Comm: syz-executor.0 Tainted: G E 5.10.209+ #1
>> Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 11/12/2020
>> Call Trace:
>> __dump_stack lib/dump_stack.c:77 [inline]
>> dump_stack+0x119/0x179 lib/dump_stack.c:118
>> debug_spin_lock_before kernel/locking/spinlock_debug.c:83 [inline]
>> do_raw_spin_lock+0x1f6/0x270 kernel/locking/spinlock_debug.c:112
>> __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:117 [inline]
>> _raw_spin_lock_irqsave+0x50/0x70 kernel/locking/spinlock.c:159
>> reset_per_cpu_data+0xe6/0x240 [drop_monitor]
>> net_dm_cmd_trace+0x43d/0x17a0 [drop_monitor]
>> genl_family_rcv_msg_doit+0x22f/0x330 net/netlink/genetlink.c:739
>> genl_family_rcv_msg net/netlink/genetlink.c:783 [inline]
>> genl_rcv_msg+0x341/0x5a0 net/netlink/genetlink.c:800
>> netlink_rcv_skb+0x14d/0x440 net/netlink/af_netlink.c:2497
>> genl_rcv+0x29/0x40 net/netlink/genetlink.c:811
>> netlink_unicast_kernel net/netlink/af_netlink.c:1322 [inline]
>> netlink_unicast+0x54b/0x800 net/netlink/af_netlink.c:1348
>> netlink_sendmsg+0x914/0xe00 net/netlink/af_netlink.c:1916
>> sock_sendmsg_nosec net/socket.c:651 [inline]
>> __sock_sendmsg+0x157/0x190 net/socket.c:663
>> ____sys_sendmsg+0x712/0x870 net/socket.c:2378
>> ___sys_sendmsg+0xf8/0x170 net/socket.c:2432
>> __sys_sendmsg+0xea/0x1b0 net/socket.c:2461
>> do_syscall_64+0x30/0x40 arch/x86/entry/common.c:46
>> entry_SYSCALL_64_after_hwframe+0x62/0xc7
>> RIP: 0033:0x7f3f9815aee9
>> 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 b0 ff ff ff f7 d8 64 89 01 48
>> RSP: 002b:00007f3f972bf0c8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
>> RAX: ffffffffffffffda RBX: 00007f3f9826d050 RCX: 00007f3f9815aee9
>> RDX: 0000000020000000 RSI: 0000000020001300 RDI: 0000000000000007
>> RBP: 00007f3f981b63bd R08: 0000000000000000 R09: 0000000000000000
>> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
>> R13: 000000000000006e R14: 00007f3f9826d050 R15: 00007ffe01ee6768
>>
>> If drop_monitor is built as a kernel module, syzkaller may have time
>> to send a netlink NET_DM_CMD_START message during the module loading.
>> This will call the net_dm_monitor_start() function that uses
>> a spinlock that has not yet been initialized.
>>
>> To fix this, let's place resource initialization above the registration
>> of a generic netlink family.
>>
>> Found by InfoTeCS on behalf of Linux Verification Center
>> (linuxtesting.org) with SVACE.
>>
>> Fixes: 9a8afc8d3962 ("Network Drop Monitor: Adding drop monitor implementation & Netlink protocol")
>> Cc: stable@xxxxxxxxxxxxxxx
>> Signed-off-by: Ilia Gavrilov <Ilia.Gavrilov@xxxxxxxxxxx>
>> ---
>> net/core/drop_monitor.c | 13 ++++++-------
>> 1 file changed, 6 insertions(+), 7 deletions(-)
>>
>> diff --git a/net/core/drop_monitor.c b/net/core/drop_monitor.c
>> index 6efd4cccc9dd..9755d2010e70 100644
>> --- a/net/core/drop_monitor.c
>> +++ b/net/core/drop_monitor.c
>> @@ -1734,6 +1734,11 @@ static int __init init_net_drop_monitor(void)
>> return -ENOSPC;
>> }
>>
>> + for_each_possible_cpu(cpu) {
>> + net_dm_cpu_data_init(cpu);
>> + net_dm_hw_cpu_data_init(cpu);
>> + }
>> +
>> rc = genl_register_family(&net_drop_monitor_family);
>
> This might be fine as-is, but it would be cleaner to move the
> registration of the netlink family to the end of the module
> initialization function, so that it's exposed to user space after all
> the preparations have been done, including the registration of the net
> device notifier.
>
Thank you for your review. I'll send it in V2.
>> if (rc) {
>> pr_err("Could not create drop monitor netlink family\n");
>> @@ -1749,11 +1754,6 @@ static int __init init_net_drop_monitor(void)
>>
>> rc = 0;
>>
>> - for_each_possible_cpu(cpu) {
>> - net_dm_cpu_data_init(cpu);
>> - net_dm_hw_cpu_data_init(cpu);
>> - }
>> -
>> goto out;
>>
>> out_unreg:
>> @@ -1772,13 +1772,12 @@ static void exit_net_drop_monitor(void)
>> * Because of the module_get/put we do in the trace state change path
>> * we are guaranteed not to have any current users when we get here
>> */
>> + BUG_ON(genl_unregister_family(&net_drop_monitor_family));
>
> Similarly, unregister the netlink family at the beginning of the module
> exit function, before unregistering the net device notifier.
>
>>
>> for_each_possible_cpu(cpu) {
>> net_dm_hw_cpu_data_fini(cpu);
>> net_dm_cpu_data_fini(cpu);
>> }
>> -
>> - BUG_ON(genl_unregister_family(&net_drop_monitor_family));
>> }
>>
>> module_init(init_net_drop_monitor);
>> --
>> 2.39.5
>>
