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af_unix: Set drop reason in manage_oob().

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AF_UNIX SOCK_STREAM socket supports MSG_OOB.

When OOB data is sent to a socket, recv() will break at that point.

If the next recv() does not have MSG_OOB, the normal data following
the OOB data is returned.

Then, the OOB skb is dropped.

Let's define a new drop reason for that case in manage_oob().

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

  # python3
  >>> from socket import *
  >>> s1, s2 = socketpair(AF_UNIX)
  >>> s1.send(b'a', MSG_OOB)
  >>> s1.send(b'b')
  >>> s2.recv(2)
  b'b'

  # cat /sys/kernel/tracing/trace_pipe
  ...
     python3-223 ... kfree_skb: ... location=unix_stream_read_generic+0x59e/0xc20 reason: UNIX_SKIP_OOB

Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://patch.msgid.link/20250116053441.5758-6-kuniyu@amazon.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Kuniyuki Iwashima 2025-01-16 14:34:38 +09:00 committed by Jakub Kicinski
parent c49a157c33
commit 533643b091
2 changed files with 7 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
include/net/dropreason-core.h
View File

@ -9,6 +9,7 @@
FN(SOCKET_CLOSE) \
FN(SOCKET_FILTER) \
FN(SOCKET_RCVBUFF) \
FN(UNIX_SKIP_OOB) \
FN(PKT_TOO_SMALL) \
FN(TCP_CSUM) \
FN(UDP_CSUM) \
@ -145,6 +146,11 @@ 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_SKIP_OOB: Out-Of-Band data is skipped by
* recv() without MSG_OOB so dropped.
*/
SKB_DROP_REASON_UNIX_SKIP_OOB,
/** @SKB_DROP_REASON_PKT_TOO_SMALL: packet size is too small */
SKB_DROP_REASON_PKT_TOO_SMALL,
/** @SKB_DROP_REASON_TCP_CSUM: TCP checksum error */

2
net/unix/af_unix.c
View File

@ -2695,7 +2695,7 @@ static struct sk_buff *manage_oob(struct sk_buff *skb, struct sock *sk,
spin_unlock(&sk->sk_receive_queue.lock);
consume_skb(read_skb);
kfree_skb(unread_skb);
kfree_skb_reason(unread_skb, SKB_DROP_REASON_UNIX_SKIP_OOB);
return skb;
}