kcm: Fix error handling for SOCK_DGRAM in kcm_sendmsg().

a22730b1 · Kuniyuki Iwashima <[email protected]> · 2023-09-11 19:27:53 -07:00

syzkaller found a memory leak in kcm_sendmsg(), and commit c821a88bd720
("kcm: Fix memory leak in error path of kcm_sendmsg()") suppressed it by
updating kcm_tx_msg(head)->last_skb if partial data is copied so that the
following sendmsg() will resume from the skb.

However, we cannot know how many bytes were copied when we get the error.
Thus, we could mess up the MSG_MORE queue.

When kcm_sendmsg() fails for SOCK_DGRAM, we should purge the queue as we
do so for UDP by udp_flush_pending_frames().

Even without this change, when the error occurred, the following sendmsg()
resumed from a wrong skb and the queue was messed up.  However, we have
yet to get such a report, and only syzkaller stumbled on it.  So, this
can be changed safely.

Note this does not change SOCK_SEQPACKET behaviour.

Fixes: c821a88bd720 ("kcm: Fix memory leak in error path of kcm_sendmsg()")
Fixes: ab7ac4eb9832 ("kcm: Kernel Connection Multiplexor module")
Signed-off-by: Kuniyuki Iwashima <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Paolo Abeni <[email protected]>

Commit: a22730b1b4bf437c6bbfdeff5feddf54be4aeada
Parents: 96f7dc69

Changes

1 files changed · +8 −7

File	Status	Add	Del	Content
net/kcm/kcmsock.c	modified	+8	−7	View file

net/kcm/kcmsock.c

View file

diff --git a/net/kcm/kcmsock.c b/net/kcm/kcmsock.c
index 740539a..dd1d8ff 100644
--- a/net/kcm/kcmsock.c
+++ b/net/kcm/kcmsock.c
@@ -930,17 +930,18 @@ partial_message:
 out_error:
 	kcm_push(kcm);
 
-	if (copied && sock->type == SOCK_SEQPACKET) {
+	if (sock->type == SOCK_SEQPACKET) {
 		/* Wrote some bytes before encountering an
 		 * error, return partial success.
 		 */
-		goto partial_message;
-	}
-
-	if (head != kcm->seq_skb)
+		if (copied)
+			goto partial_message;
+		if (head != kcm->seq_skb)
+			kfree_skb(head);
+	} else {
 		kfree_skb(head);
-	else if (copied)
-		kcm_tx_msg(head)->last_skb = skb;
+		kcm->seq_skb = NULL;
+	}
 
 	err = sk_stream_error(sk, msg->msg_flags, err);
 