Fix possible deadlock in UDP.Write().

In UDP endpoint.Write() sendUDP is called with e.mu Rlocked. But if this happens
to send a datagram over loopback which ends up generating an ICMP response of
say ErrNoPortReachable, the handling of the response in HandleControlPacket also
acquires e.mu using RLock. This is mostly fine unless there is a competing
caller trying to acquire e.mu in exclusive mode using Lock(). This will deadlock
as a caller waiting in Lock() disallows an new RLocks() to ensure it can
actually acquire the Lock.

This is documented here https://golang.org/pkg/sync/#RWMutex.

This change releases the endpoint mutex before calling sendUDP to resolve the
possibility of the deadlock.

Reported-by: syzbot+537989797548c66e8ee3@syzkaller.appspotmail.com
Reported-by: syzbot+eb0b73b4ab486f7673ba@syzkaller.appspotmail.com
PiperOrigin-RevId: 342894148

0 files changed, 0 insertions, 0 deletions