[PATCH 5.11 077/210] net: let skb_orphan_partial wake-up waiters.

Greg Kroah-Hartman
2021-04-12T09:31:06Z

From: Paolo Abeni <pabeni@redhat.com>

commit 9adc89af724f12a03b47099cd943ed54e877cd59 upstream.

Currently the mentioned helper can end-up freeing the socket wmem
without waking-up any processes waiting for more write memory.

If the partially orphaned skb is attached to an UDP (or raw) socket,
the lack of wake-up can hang the user-space.

Even for TCP sockets not calling the sk destructor could have bad
effects on TSQ.

Address the issue using skb_orphan to release the sk wmem before
setting the new sock_efree destructor. Additionally bundle the
whole ownership update in a new helper, so that later other
potential users could avoid duplicate code.

v1 -> v2:
- use skb_orphan() instead of sort of open coding it (Eric)
- provide an helper for the ownership change (Eric)

Fixes: f6ba8d33cfbb ("netem: fix skb_orphan_partial()")
Suggested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
include/net/sock.h | 9 +++++++++
net/core/sock.c | 12 +++---------
2 files changed, 12 insertions(+), 9 deletions(-)

--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -2215,6 +2215,15 @@ static inline void skb_set_owner_r(struc
sk_mem_charge(sk, skb->truesize);
}

+static inline void skb_set_owner_sk_safe(struct sk_buff *skb, struct sock *sk)
+{
+ if (sk && refcount_inc_not_zero(&sk->sk_refcnt)) {
+ skb_orphan(skb);
+ skb->destructor = sock_efree;
+ skb->sk = sk;
+ }
+}
+
void sk_reset_timer(struct sock *sk, struct timer_list *timer,
unsigned long expires);

--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -2118,16 +2118,10 @@ void skb_orphan_partial(struct sk_buff *
if (skb_is_tcp_pure_ack(skb))
return;

- if (can_skb_orphan_partial(skb)) {
- struct sock *sk = skb->sk;
-
- if (refcount_inc_not_zero(&sk->sk_refcnt)) {
- WARN_ON(refcount_sub_and_test(skb->truesize, &sk->sk_wmem_alloc));
- skb->destructor = sock_efree;
- }
- } else {
+ if (can_skb_orphan_partial(skb))
+ skb_set_owner_sk_safe(skb, skb->sk);
+ else
skb_orphan(skb);
- }
}
EXPORT_SYMBOL(skb_orphan_partial);