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authorEric Dumazet <edumazet@google.com>2019-07-19 11:52:33 -0700
committerDavid S. Miller <davem@davemloft.net>2019-07-21 20:41:24 -0700
commitb617158dc096709d8600c53b6052144d12b89fab (patch)
treeb3f0cd2d20413a1b0e7ccd7e16d7690810e3f1cd
parentbe4363bdf0ce9530f15aa0a03d1060304d116b15 (diff)
downloadlinux-stericsson-b617158dc096709d8600c53b6052144d12b89fab.tar.gz
tcp: be more careful in tcp_fragment()
Some applications set tiny SO_SNDBUF values and expect TCP to just work. Recent patches to address CVE-2019-11478 broke them in case of losses, since retransmits might be prevented. We should allow these flows to make progress. This patch allows the first and last skb in retransmit queue to be split even if memory limits are hit. It also adds the some room due to the fact that tcp_sendmsg() and tcp_sendpage() might overshoot sk_wmem_queued by about one full TSO skb (64KB size). Note this allowance was already present in stable backports for kernels < 4.15 Note for < 4.15 backports : tcp_rtx_queue_tail() will probably look like : static inline struct sk_buff *tcp_rtx_queue_tail(const struct sock *sk) { struct sk_buff *skb = tcp_send_head(sk); return skb ? tcp_write_queue_prev(sk, skb) : tcp_write_queue_tail(sk); } Fixes: f070ef2ac667 ("tcp: tcp_fragment() should apply sane memory limits") Signed-off-by: Eric Dumazet <edumazet@google.com> Reported-by: Andrew Prout <aprout@ll.mit.edu> Tested-by: Andrew Prout <aprout@ll.mit.edu> Tested-by: Jonathan Lemon <jonathan.lemon@gmail.com> Tested-by: Michal Kubecek <mkubecek@suse.cz> Acked-by: Neal Cardwell <ncardwell@google.com> Acked-by: Yuchung Cheng <ycheng@google.com> Acked-by: Christoph Paasch <cpaasch@apple.com> Cc: Jonathan Looney <jtl@netflix.com> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--include/net/tcp.h5
-rw-r--r--net/ipv4/tcp_output.c13
2 files changed, 16 insertions, 2 deletions
diff --git a/include/net/tcp.h b/include/net/tcp.h
index f42d300f0cfa..e5cf514ba118 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -1709,6 +1709,11 @@ static inline struct sk_buff *tcp_rtx_queue_head(const struct sock *sk)
return skb_rb_first(&sk->tcp_rtx_queue);
}
+static inline struct sk_buff *tcp_rtx_queue_tail(const struct sock *sk)
+{
+ return skb_rb_last(&sk->tcp_rtx_queue);
+}
+
static inline struct sk_buff *tcp_write_queue_head(const struct sock *sk)
{
return skb_peek(&sk->sk_write_queue);
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 4af1f5dae9d3..6e4afc48d7bb 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -1288,6 +1288,7 @@ int tcp_fragment(struct sock *sk, enum tcp_queue tcp_queue,
struct tcp_sock *tp = tcp_sk(sk);
struct sk_buff *buff;
int nsize, old_factor;
+ long limit;
int nlen;
u8 flags;
@@ -1298,8 +1299,16 @@ int tcp_fragment(struct sock *sk, enum tcp_queue tcp_queue,
if (nsize < 0)
nsize = 0;
- if (unlikely((sk->sk_wmem_queued >> 1) > sk->sk_sndbuf &&
- tcp_queue != TCP_FRAG_IN_WRITE_QUEUE)) {
+ /* tcp_sendmsg() can overshoot sk_wmem_queued by one full size skb.
+ * We need some allowance to not penalize applications setting small
+ * SO_SNDBUF values.
+ * Also allow first and last skb in retransmit queue to be split.
+ */
+ limit = sk->sk_sndbuf + 2 * SKB_TRUESIZE(GSO_MAX_SIZE);
+ if (unlikely((sk->sk_wmem_queued >> 1) > limit &&
+ tcp_queue != TCP_FRAG_IN_WRITE_QUEUE &&
+ skb != tcp_rtx_queue_head(sk) &&
+ skb != tcp_rtx_queue_tail(sk))) {
NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPWQUEUETOOBIG);
return -ENOMEM;
}