From: Willem de Bruijn willemb@google.com
[ Upstream commit 100f6d8e09905c59be45b6316f8f369c0be1b2d8 ]
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: 52900d22288e7 ("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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- net/core/skbuff.c | 6 +++++- net/ipv4/ip_output.c | 4 ++-- net/ipv6/ip6_output.c | 4 ++-- 3 files changed, 9 insertions(+), 5 deletions(-)
--- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -1001,7 +1001,11 @@ struct ubuf_info *sock_zerocopy_realloc( uarg->len++; uarg->bytelen = bytelen; atomic_set(&sk->sk_zckey, ++next); - sock_zerocopy_get(uarg); + + /* no extra ref when appending to datagram (MSG_MORE) */ + if (sk->sk_type == SOCK_STREAM) + sock_zerocopy_get(uarg); + return uarg; } } --- a/net/ipv4/ip_output.c +++ b/net/ipv4/ip_output.c @@ -883,7 +883,7 @@ static int __ip_append_data(struct sock 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); @@ -923,7 +923,7 @@ static int __ip_append_data(struct sock 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; --- a/net/ipv6/ip6_output.c +++ b/net/ipv6/ip6_output.c @@ -1275,7 +1275,7 @@ static int __ip6_append_data(struct sock 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;