Commit b3e365bb authored by Kuniyuki Iwashima's avatar Kuniyuki Iwashima Committed by Jakub Kicinski
Browse files

af_unix: Set drop reason in unix_dgram_disconnected(). 



unix_dgram_disconnected() is called from two places:

  1. when a connect()ed socket dis-connect()s or re-connect()s to
     another socket

  2. when sendmsg() fails because the peer socket that the client
     has connect()ed to has been close()d

Then, the client's recv queue is purged to remove all messages from
the old peer socket.

Let's define a new drop reason for that case.

  # echo 1 > /sys/kernel/tracing/events/skb/kfree_skb/enable

  # python3
  >>> from socket import *
  >>>
  >>> # s1 has a message from s2
  >>> s1, s2 = socketpair(AF_UNIX, SOCK_DGRAM)
  >>> s2.send(b'hello world')
  >>>
  >>> # re-connect() drops the message from s2
  >>> s3 = socket(AF_UNIX, SOCK_DGRAM)
  >>> s3.bind('')
  >>> s1.connect(s3.getsockname())

  # cat /sys/kernel/tracing/trace_pipe
     python3-250 ... kfree_skb: ... location=skb_queue_purge_reason+0xdc/0x110 reason: UNIX_DISCONNECT

Signed-off-by: default avatarKuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20250116053441.5758-8-kuniyu@amazon.com


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent bace4b46

include/net/dropreason-core.h

+7 −0
Original line number Diff line number Diff line
@@ -9,6 +9,7 @@ 
	FN(SOCKET_CLOSE)		\

	FN(SOCKET_FILTER)		\

	FN(SOCKET_RCVBUFF)		\

	FN(UNIX_DISCONNECT)		\

	FN(UNIX_SKIP_OOB)		\

	FN(PKT_TOO_SMALL)		\

	FN(TCP_CSUM)			\
@@ -146,6 +147,12 @@ enum skb_drop_reason { 
	SKB_DROP_REASON_SOCKET_FILTER,

	/** @SKB_DROP_REASON_SOCKET_RCVBUFF: socket receive buff is full */

	SKB_DROP_REASON_SOCKET_RCVBUFF,

	/**

	 * @SKB_DROP_REASON_UNIX_DISCONNECT: recv queue is purged when SOCK_DGRAM

	 * or SOCK_SEQPACKET socket re-connect()s to another socket or notices

	 * during send() that the peer has been close()d.

	 */

	SKB_DROP_REASON_UNIX_DISCONNECT,

	/**

	 * @SKB_DROP_REASON_UNIX_SKIP_OOB: Out-Of-Band data is skipped by

	 * recv() without MSG_OOB so dropped.

net/unix/af_unix.c

+3 −1
Original line number Diff line number Diff line
@@ -622,7 +622,9 @@ static void unix_write_space(struct sock *sk) 
static void unix_dgram_disconnected(struct sock *sk, struct sock *other)

{

	if (!skb_queue_empty(&sk->sk_receive_queue)) {

		skb_queue_purge(&sk->sk_receive_queue);

		skb_queue_purge_reason(&sk->sk_receive_queue,

				       SKB_DROP_REASON_UNIX_DISCONNECT);



		wake_up_interruptible_all(&unix_sk(sk)->peer_wait);



		/* If one link of bidirectional dgram pipe is disconnected,