Re: [next] unix stream crashes

[Yan, Zheng]

The skb can be destructed before the while loop in unix_stream_sendmsg stops.
please try below patch.

---
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index e6d9d10..f6d7ed7 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1577,6 +1577,7 @@ static int unix_stream_sendmsg(struct kiocb
*kiocb, struct socket *sock,
 	int sent = 0;
 	struct scm_cookie tmp_scm;
 	bool fds_sent = false;
+	bool scm_ref = true;
 	int max_level;

 	if (NULL == siocb->scm)
@@ -1637,12 +1638,19 @@ static int unix_stream_sendmsg(struct kiocb
*kiocb, struct socket *sock,
 		 */
 		size = min_t(int, size, skb_tailroom(skb));

+		/*
+		 * pass the scm reference to the skb if a single skb is large
+		 * enough to hold all data.
+		 */
+		if (!fds_sent && sent + size >= len)
+			scm_ref = false;

-		/* Only send the fds and no ref to pid in the first buffer */
-		err = unix_scm_to_skb(siocb->scm, skb, !fds_sent, fds_sent);
+		/* Only send the fds in the first buffer */
+		err = unix_scm_to_skb(siocb->scm, skb, !fds_sent,
+					fds_sent || scm_ref);
 		if (err < 0) {
 			kfree_skb(skb);
-			goto out;
+			goto out_err;
 		}
 		max_level = err + 1;
 		fds_sent = true;
@@ -1650,7 +1658,7 @@ static int unix_stream_sendmsg(struct kiocb
*kiocb, struct socket *sock,
 		err = memcpy_fromiovec(skb_put(skb, size), msg->msg_iov, size);
 		if (err) {
 			kfree_skb(skb);
-			goto out;
+			goto out_err;
 		}

 		unix_state_lock(other);
@@ -1667,10 +1675,10 @@ static int unix_stream_sendmsg(struct kiocb
*kiocb, struct socket *sock,
 		sent += size;
 	}

-	if (skb)
-		scm_release(siocb->scm);
-	else
+	if (scm_ref)
 		scm_destroy(siocb->scm);
+	else
+		scm_release(siocb->scm);
 	siocb->scm = NULL;

 	return sent;
@@ -1683,9 +1691,10 @@ pipe_err:
 		send_sig(SIGPIPE, current, 0);
 	err = -EPIPE;
 out_err:
-	if (skb == NULL)
+	if (scm_ref)
 		scm_destroy(siocb->scm);
-out:
+	else
+		scm_release(siocb->scm);
 	siocb->scm = NULL;
 	return sent ? : err;
 }


On Sat, Sep 3, 2011 at 2:23 PM, Jiri Slaby <jirislaby@xxxxxxxxx> wrote:
> On 09/03/2011 07:54 AM, Sedat Dilek wrote:
>>
>> I saw similiar call-traces with put_cred_rcu() - besides with
>> kmem_cache_alloc_trace().
>> My post-it says:
>> Kernel panic - not syncing: CRED: put_cred_rcu sees f67ac0c0 with usage
>> -43
>
> Hm, Tim, it looks like you put a pid which you did not get?
>
> regards,
> --
> js
> --
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