Re: [PATCH net-next] virtio-net: fix use-after-free in page_to_skb()

["Michael S. Tsirkin" <mst@redhat.com>]

On Tue, Apr 20, 2021 at 02:43:41AM -0700, Eric Dumazet wrote:
> From: Eric Dumazet <edumazet@google.com>
> 
> KASAN/syzbot had 4 reports, one of them being:
> 
> BUG: KASAN: slab-out-of-bounds in memcpy include/linux/fortify-string.h:191 [inline]
> BUG: KASAN: slab-out-of-bounds in page_to_skb+0x5cf/0xb70 drivers/net/virtio_net.c:480
> Read of size 12 at addr ffff888014a5f800 by task systemd-udevd/8445
> 
> CPU: 0 PID: 8445 Comm: systemd-udevd Not tainted 5.12.0-rc8-next-20210419-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
>  <IRQ>
>  __dump_stack lib/dump_stack.c:79 [inline]
>  dump_stack+0x141/0x1d7 lib/dump_stack.c:120
>  print_address_description.constprop.0.cold+0x5b/0x2f8 mm/kasan/report.c:233
>  __kasan_report mm/kasan/report.c:419 [inline]
>  kasan_report.cold+0x7c/0xd8 mm/kasan/report.c:436
>  check_region_inline mm/kasan/generic.c:180 [inline]
>  kasan_check_range+0x13d/0x180 mm/kasan/generic.c:186
>  memcpy+0x20/0x60 mm/kasan/shadow.c:65
>  memcpy include/linux/fortify-string.h:191 [inline]
>  page_to_skb+0x5cf/0xb70 drivers/net/virtio_net.c:480
>  receive_mergeable drivers/net/virtio_net.c:1009 [inline]
>  receive_buf+0x2bc0/0x6250 drivers/net/virtio_net.c:1119
>  virtnet_receive drivers/net/virtio_net.c:1411 [inline]
>  virtnet_poll+0x568/0x10b0 drivers/net/virtio_net.c:1516
>  __napi_poll+0xaf/0x440 net/core/dev.c:6962
>  napi_poll net/core/dev.c:7029 [inline]
>  net_rx_action+0x801/0xb40 net/core/dev.c:7116
>  __do_softirq+0x29b/0x9fe kernel/softirq.c:559
>  invoke_softirq kernel/softirq.c:433 [inline]
>  __irq_exit_rcu+0x136/0x200 kernel/softirq.c:637
>  irq_exit_rcu+0x5/0x20 kernel/softirq.c:649
>  common_interrupt+0xa4/0xd0 arch/x86/kernel/irq.c:240
> 
> Fixes: fb32856b16ad ("virtio-net: page_to_skb() use build_skb when there's sufficient tailroom")
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Reported-by: syzbot <syzkaller@googlegroups.com>
> Reported-by: Guenter Roeck <linux@roeck-us.net>
> Reported-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
> Cc: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
> Cc: Jason Wang <jasowang@redhat.com>
> Cc: "Michael S. Tsirkin" <mst@redhat.com>
> Cc: virtualization@lists.linux-foundation.org

Acked-by: Michael S. Tsirkin <mst@redhat.com>

> ---
>  drivers/net/virtio_net.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
> index 8cd76037c72481200ea3e8429e9fdfec005dad85..2e28c04aa6351d2b4016f7d277ce104c4970069d 100644
> --- a/drivers/net/virtio_net.c
> +++ b/drivers/net/virtio_net.c
> @@ -385,6 +385,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>  	struct sk_buff *skb;
>  	struct virtio_net_hdr_mrg_rxbuf *hdr;
>  	unsigned int copy, hdr_len, hdr_padded_len;
> +	struct page *page_to_free = NULL;
>  	int tailroom, shinfo_size;
>  	char *p, *hdr_p;
>  
> @@ -445,7 +446,7 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>  		if (len)
>  			skb_add_rx_frag(skb, 0, page, offset, len, truesize);
>  		else
> -			put_page(page);
> +			page_to_free = page;
>  		goto ok;
>  	}
>  
> @@ -479,6 +480,8 @@ static struct sk_buff *page_to_skb(struct virtnet_info *vi,
>  		hdr = skb_vnet_hdr(skb);
>  		memcpy(hdr, hdr_p, hdr_len);
>  	}
> +	if (page_to_free)
> +		put_page(page_to_free);
>  
>  	if (metasize) {
>  		__skb_pull(skb, metasize);
> -- 
> 2.31.1.368.gbe11c130af-goog