From: Soheil Hassas Yeganeh <soh...@google.com>
Do not set sk_err when dequeuing errors from the error queue.
Doing so results in:
a) Bugs: By overwriting existing sk_err values, it possibly
hides legitimate errors. It is also incorrect when local
errors are queued with ip_local_error. That happens in the
context of a system call, which already returns the error
code.
b) Inconsistent behavior: When there are pending errors on
the error queue, sk_err is sometimes 0 (e.g., for
the first timestamp on the error queue) and sometimes
set to an error code (after dequeuing the first
timestamp).
c) Suboptimality: Setting sk_err to ENOMSG on simple
TX timestamps can abort parallel reads and writes.
Removing this line doesn't break userspace. This is because
userspace code cannot rely on sk_err for detecting whether
there is something on the error queue. Except for ICMP messages
received for UDP and RAW, sk_err is not set at enqueue time,
and as a result sk_err can be 0 while there are plenty of
errors on the error queue.
For ICMP packets in UDP and RAW, sk_err is set when they are
enqueued on the error queue, but that does not result in aborting
reads and writes. For such cases, sk_err is only readable via
getsockopt(SO_ERROR) which will reset the value of sk_err on
its own. More importantly, prior to this patch,
recvmsg(MSG_ERRQUEUE) has a race on setting sk_err (i.e.,
sk_err is set by sock_dequeue_err_skb without atomic ops or
locks) which can store 0 in sk_err even when we have ICMP
messages pending. Removing this line from sock_dequeue_err_skb
eliminates that race.
Signed-off-by: Soheil Hassas Yeganeh <soh...@google.com>
Signed-off-by: Eric Dumazet <eduma...@google.com>
Signed-off-by: Willem de Bruijn <will...@google.com>
Signed-off-by: Neal Cardwell <ncardw...@google.com>
---
net/core/skbuff.c | 1 -
1 file changed, 1 deletion(-)
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 1e3e008..0b2a6e9 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -3725,7 +3725,6 @@ struct sk_buff *sock_dequeue_err_skb(struct sock *sk)
err = SKB_EXT_ERR(skb_next)->ee.ee_errno;
spin_unlock_irqrestore(&q->lock, flags);
- sk->sk_err = err;
if (err)
sk->sk_error_report(sk);
--
2.8.0.rc3.226.g39d4020
