net: correct zerocopy refcnt with udp MSG_MORE (100f6d8e) · Commits · 戴 / test

TCP zerocopy takes a uarg reference for every skb, plus one for the tcp_sendmsg_locked datapath temporarily, to avoid reaching refcnt zero as it builds, sends and frees skbs inside its inner loop. UDP and RAW zerocopy do not send inside the inner loop so do not need the extra sock_zerocopy_get + sock_zerocopy_put pair. Commit 52900d22288ed ("udp: elide zerocopy operation in hot path") introduced extra_uref to pass the initial reference taken in sock_zerocopy_alloc to the first generated skb. But, sock_zerocopy_realloc takes this extra reference at the start of every call. With MSG_MORE, no new skb may be generated to attach the extra_uref to, so refcnt is incorrectly 2 with only one skb. Do not take the extra ref if uarg && !tcp, which implies MSG_MORE. Update extra_uref accordingly. This conditional assignment triggers a false positive may be used uninitialized warning, so have to initialize extra_uref at define. Changes v1->v2: fix typo in Fixes SHA1 Fixes: ("udp: elide zerocopy operation in hot path") Reported-by:

syzbot <syzkaller@googlegroups.com> Diagnosed-by:

Eric Dumazet <edumazet@google.com> Signed-off-by:

Willem de Bruijn <willemb@google.com> Signed-off-by:

David S. Miller <davem@davemloft.net>

net/core/skbuff.c

+5 −1

Original line number	Diff line number	Diff line
		@@ -1036,7 +1036,11 @@ struct ubuf_info sock_zerocopy_realloc(struct sock sk, size_t size,
		uarg->len++;
		uarg->bytelen = bytelen;
		atomic_set(&sk->sk_zckey, ++next);

		/* no extra ref when appending to datagram (MSG_MORE) */
		if (sk->sk_type == SOCK_STREAM)
		sock_zerocopy_get(uarg);

		return uarg;
		}
		}

net/ipv4/ip_output.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -878,7 +878,7 @@ static int __ip_append_data(struct sock *sk,
		int csummode = CHECKSUM_NONE;
		struct rtable rt = (struct rtable )cork->dst;
		unsigned int wmem_alloc_delta = 0;
		bool paged, extra_uref;
		bool paged, extra_uref = false;
		u32 tskey = 0;

		skb = skb_peek_tail(queue);
		@@ -918,7 +918,7 @@ static int __ip_append_data(struct sock *sk,
		uarg = sock_zerocopy_realloc(sk, length, skb_zcopy(skb));
		if (!uarg)
		return -ENOBUFS;
		extra_uref = true;
		extra_uref = !skb; /* only extra ref if !MSG_MORE */
		if (rt->dst.dev->features & NETIF_F_SG &&
		csummode == CHECKSUM_PARTIAL) {
		paged = true;

net/ipv6/ip6_output.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -1275,7 +1275,7 @@ static int __ip6_append_data(struct sock *sk,
		int csummode = CHECKSUM_NONE;
		unsigned int maxnonfragsize, headersize;
		unsigned int wmem_alloc_delta = 0;
		bool paged, extra_uref;
		bool paged, extra_uref = false;

		skb = skb_peek_tail(queue);
		if (!skb) {
		@@ -1344,7 +1344,7 @@ emsgsize:
		uarg = sock_zerocopy_realloc(sk, length, skb_zcopy(skb));
		if (!uarg)
		return -ENOBUFS;
		extra_uref = true;
		extra_uref = !skb; /* only extra ref if !MSG_MORE */
		if (rt->dst.dev->features & NETIF_F_SG &&
		csummode == CHECKSUM_PARTIAL) {
		paged = true;

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