tun: mark small packets as owned by the tap sock (4b663366) · Commits · 戴 / test

- v1 -> v2: Move skb_set_owner_w to __tun_build_skb to reduce patch size Small packets going out of a tap device go through an optimized code path that uses build_skb() rather than sock_alloc_send_pskb(). The latter calls skb_set_owner_w(), but the small packet code path does not. The net effect is that small packets are not owned by the userland application's socket (e.g. QEMU), while large packets are. This can be seen with a TCP session, where packets are not owned when the window size is small enough (around PAGE_SIZE), while they are once the window grows (note that this requires the host to support virtio tso for the guest to offload segmentation). All this leads to inconsistent behaviour in the kernel, especially on netfilter modules that uses sk->socket (e.g. xt_owner). Fixes: ("tap: use build_skb() for small packet") Signed-off-by:

Alexis Bauvin <abauvin@scaleway.com> Acked-by:

Jason Wang <jasowang@redhat.com> Signed-off-by:

David S. Miller <davem@davemloft.net>

drivers/net/tun.c

+6 −3

Original line number	Diff line number	Diff line
		@@ -1599,7 +1599,8 @@ static bool tun_can_build_skb(struct tun_struct tun, struct tun_file tfile,
		return true;
		}

		static struct sk_buff __tun_build_skb(struct page_frag alloc_frag, char *buf,
		static struct sk_buff __tun_build_skb(struct tun_file tfile,
		struct page_frag alloc_frag, char buf,
		int buflen, int len, int pad)
		{
		struct sk_buff *skb = build_skb(buf, buflen);
		@@ -1609,6 +1610,7 @@ static struct sk_buff __tun_build_skb(struct page_frag alloc_frag, char *buf,

		skb_reserve(skb, pad);
		skb_put(skb, len);
		skb_set_owner_w(skb, tfile->socket.sk);

		get_page(alloc_frag->page);
		alloc_frag->offset += buflen;
		@@ -1686,7 +1688,8 @@ static struct sk_buff tun_build_skb(struct tun_struct tun,
		*/
		if (hdr->gso_type \|\| !xdp_prog) {
		*skb_xdp = 1;
		return __tun_build_skb(alloc_frag, buf, buflen, len, pad);
		return __tun_build_skb(tfile, alloc_frag, buf, buflen, len,
		pad);
		}

		*skb_xdp = 0;
		@@ -1723,7 +1726,7 @@ static struct sk_buff tun_build_skb(struct tun_struct tun,
		rcu_read_unlock();
		local_bh_enable();

		return __tun_build_skb(alloc_frag, buf, buflen, len, pad);
		return __tun_build_skb(tfile, alloc_frag, buf, buflen, len, pad);

		err_xdp:
		put_page(alloc_frag->page);

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