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af_unix: Set drop reason in unix_dgram_disconnected().

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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: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20250116053441.5758-8-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Kuniyuki Iwashima 2025-01-16 14:34:40 +09:00 committed by Jakub Kicinski
parent bace4b4680
commit b3e365bbf4
2 changed files with 10 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
include/net/dropreason-core.h
View File

@ -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.

4
net/unix/af_unix.c
View File

@ -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,