Subject: Re: [PATCH net] virtio-net: fix overflow inside virtnet_rq_alloc

From: Darren Kenny <[email-masked]>
Date: Wed, 21 Aug 2024 17:47:06 +0100

Hi Michael,

On Tuesday, 2024-08-20 at 12:50:39 -04, Michael S. Tsirkin wrote:
> On Tue, Aug 20, 2024 at 03:19:13PM +0800, Xuan Zhuo wrote:
>> leads to regression on VM with the sysctl value of:
>> 
>> - net.core.high_order_alloc_disable=1
>
>
>
>
>> which could see reliable crashes or scp failure (scp a file 100M in size
>> to VM):
>> 
>> The issue is that the virtnet_rq_dma takes up 16 bytes at the beginning
>> of a new frag. When the frag size is larger than PAGE_SIZE,
>> everything is fine. However, if the frag is only one page and the
>> total size of the buffer and virtnet_rq_dma is larger than one page, an
>> overflow may occur. In this case, if an overflow is possible, I adjust
>> the buffer size. If net.core.high_order_alloc_disable=1, the maximum
>> buffer size is 4096 - 16. If net.core.high_order_alloc_disable=0, only
>> the first buffer of the frag is affected.
>> 
>> Fixes: f9dac92ba908 ("virtio_ring: enable premapped mode whatever use_dma_api")
>> Reported-by: "Si-Wei Liu" <[email-masked]>
>> Closes: http://lore.kernel.org/all/[email-masked]
>> Signed-off-by: Xuan Zhuo <[email-masked]>
>
>
> Darren, could you pls test and confirm?

Unfortunately with this change I seem to still get a panic as soon as I start a
download using wget:

[  144.055630] Kernel panic - not syncing: corrupted stack end detected inside scheduler
[  144.056249] CPU: 8 PID: 37894 Comm: sleep Kdump: loaded Not tainted 6.10.0-1.el8uek.x86_64 #2
[  144.056850] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.0-4.module+el8.9.0+90173+a3f3e83a 04/01/2014
[  144.057585] Call Trace:
[  144.057791]  <TASK>
[  144.057973]  panic+0x347/0x370
[  144.058223]  schedule_debug.isra.0+0xfb/0x100
[  144.058565]  __schedule+0x58/0x6a0
[  144.058838]  ? refill_stock+0x26/0x50
[  144.059120]  ? srso_alias_return_thunk+0x5/0xfbef5
[  144.059473]  do_task_dead+0x42/0x50
[  144.059752]  do_exit+0x31e/0x4b0
[  144.060011]  ? __audit_syscall_entry+0xee/0x150
[  144.060352]  do_group_exit+0x30/0x80
[  144.060633]  __x64_sys_exit_group+0x18/0x20
[  144.060946]  do_syscall_64+0x8c/0x1c0
[  144.061228]  ? srso_alias_return_thunk+0x5/0xfbef5
[  144.061570]  ? __audit_filter_op+0xbe/0x140
[  144.061873]  ? srso_alias_return_thunk+0x5/0xfbef5
[  144.062204]  ? audit_reset_context+0x232/0x310
[  144.062514]  ? srso_alias_return_thunk+0x5/0xfbef5
[  144.062851]  ? syscall_exit_work+0x103/0x130
[  144.063148]  ? srso_alias_return_thunk+0x5/0xfbef5
[  144.063473]  ? syscall_exit_to_user_mode+0x77/0x220
[  144.063813]  ? srso_alias_return_thunk+0x5/0xfbef5
[  144.064142]  ? do_syscall_64+0xb9/0x1c0
[  144.064411]  ? srso_alias_return_thunk+0x5/0xfbef5
[  144.064747]  ? do_syscall_64+0xb9/0x1c0
[  144.065018]  ? srso_alias_return_thunk+0x5/0xfbef5
[  144.065345]  ? do_read_fault+0x109/0x1b0
[  144.065628]  ? srso_alias_return_thunk+0x5/0xfbef5
[  144.065961]  ? do_fault+0x1aa/0x2f0
[  144.066212]  ? handle_pte_fault+0x102/0x1a0
[  144.066503]  ? srso_alias_return_thunk+0x5/0xfbef5
[  144.066836]  ? __handle_mm_fault+0x5ed/0x710
[  144.067137]  ? srso_alias_return_thunk+0x5/0xfbef5
[  144.067464]  ? __count_memcg_events+0x72/0x110
[  144.067779]  ? srso_alias_return_thunk+0x5/0xfbef5
[  144.068106]  ? count_memcg_events.constprop.0+0x26/0x50
[  144.068457]  ? srso_alias_return_thunk+0x5/0xfbef5
[  144.068788]  ? handle_mm_fault+0xae/0x320
[  144.069068]  ? srso_alias_return_thunk+0x5/0xfbef5
[  144.069395]  ? do_user_addr_fault+0x34a/0x6b0
[  144.069708]  entry_SYSCALL_64_after_hwframe+0x76/0x7e
[  144.070049] RIP: 0033:0x7fc5524f9c66
[  144.070307] Code: Unable to access opcode bytes at 0x7fc5524f9c3c.
[  144.070720] RSP: 002b:00007ffee052beb8 EFLAGS: 00000246 ORIG_RAX: 00000000000000e7
[  144.071214] RAX: ffffffffffffffda RBX: 00007fc5527bb860 RCX: 00007fc5524f9c66
[  144.071684] RDX: 0000000000000000 RSI: 000000000000003c RDI: 0000000000000000
[  144.072146] RBP: 0000000000000000 R08: 00000000000000e7 R09: ffffffffffffff78
[  144.072608] R10: 00007ffee052bdef R11: 0000000000000246 R12: 00007fc5527bb860
[  144.073076] R13: 0000000000000002 R14: 00007fc5527c4528 R15: 0000000000000000
[  144.073543]  </TASK>
[  144.074780] Kernel Offset: 0x37c00000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff)

Thanks,

Darren.

>> ---
>>  drivers/net/virtio_net.c | 12 +++++++++---
>>  1 file changed, 9 insertions(+), 3 deletions(-)
>> 
>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
>> index c6af18948092..e5286a6da863 100644
>> --- a/drivers/net/virtio_net.c
>> +++ b/drivers/net/virtio_net.c
>> @@ -918,9 +918,6 @@ static void *virtnet_rq_alloc(struct receive_queue *rq, u32 size, gfp_t gfp)
>>  	void *buf, *head;
>>  	dma_addr_t addr;
>>  
>> -	if (unlikely(!skb_page_frag_refill(size, alloc_frag, gfp)))
>> -		return NULL;
>> -
>>  	head = page_address(alloc_frag->page);
>>  
>>  	dma = head;
>> @@ -2421,6 +2418,9 @@ static int add_recvbuf_small(struct virtnet_info *vi, struct receive_queue *rq,
>>  	len = SKB_DATA_ALIGN(len) +
>>  	      SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
>>  
>> +	if (unlikely(!skb_page_frag_refill(len, &rq->alloc_frag, gfp)))
>> +		return -ENOMEM;
>> +
>>  	buf = virtnet_rq_alloc(rq, len, gfp);
>>  	if (unlikely(!buf))
>>  		return -ENOMEM;
>> @@ -2521,6 +2521,12 @@ static int add_recvbuf_mergeable(struct virtnet_info *vi,
>>  	 */
>>  	len = get_mergeable_buf_len(rq, &rq->mrg_avg_pkt_len, room);
>>  
>> +	if (unlikely(!skb_page_frag_refill(len + room, alloc_frag, gfp)))
>> +		return -ENOMEM;
>> +
>> +	if (!alloc_frag->offset && len + room + sizeof(struct virtnet_rq_dma) > alloc_frag->size)
>> +		len -= sizeof(struct virtnet_rq_dma);
>> +
>>  	buf = virtnet_rq_alloc(rq, len + room, gfp);
>>  	if (unlikely(!buf))
>>  		return -ENOMEM;
>> -- 
>> 2.32.0.3.g01195cf9f