Here's what I think is a better patch. Or maybe just simpler.
However, I'm still unsure what the effect of this patch on
file descriptor passing might be. Reading the prior code,
and the parallel portions/comments in unix_dgram_recvmsg(),
it looks like there's been a lot of uncertainty as to how
file descriptor passing should be handled durning MSG_PEEK
operations. To quote:
/* It is questionable: on PEEK we could:
- do not return fds - good, but too simple 8)
- return fds, and do not return them on read (old strategy,
apparently wrong)
- clone fds (I chose it for now, it is the most universal
solution)
POSIX 1003.1g does not actually define this clearly
at all. POSIX 1003.1g doesn't define a lot of things
clearly however!
*/
With this patch, passed file descriptors are ignored during MSG_PEEK.
This is essentially the first case in the comment above. What I
can't seem to figure out is why this is incorrect. I suspect there's
some history here that I can't find via Google, mailing list archives,
or revision logs.
So, that said, here's a cleaner patch. It's still not ready for
application until the file descriptor passing is better understood.
Thanks,
Brent
diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
index 060bba4..6d6cdb4 100644
--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1750,6 +1750,8 @@ static int unix_stream_recvmsg(struct ki
int target;
int err = 0;
long timeo;
+ struct sk_buff *skb;
+ struct sk_buff_head peek_stack;
err = -EINVAL;
if (sk->sk_state != TCP_ESTABLISHED)
@@ -1759,6 +1761,9 @@ static int unix_stream_recvmsg(struct ki
if (flags&MSG_OOB)
goto out;
+ if (flags & MSG_PEEK)
+ skb_queue_head_init(&peek_stack);
+
target = sock_rcvlowat(sk, flags&MSG_WAITALL, size);
timeo = sock_rcvtimeo(sk, flags&MSG_DONTWAIT);
@@ -1778,7 +1783,6 @@ static int unix_stream_recvmsg(struct ki
do
{
int chunk;
- struct sk_buff *skb;
unix_state_lock(sk);
skb = skb_dequeue(&sk->sk_receive_queue);
@@ -1864,19 +1868,14 @@ static int unix_stream_recvmsg(struct ki
if (siocb->scm->fp)
break;
- }
- else
- {
- /* It is questionable, see note in unix_dgram_recvmsg.
- */
- if (UNIXCB(skb).fp)
- siocb->scm->fp = scm_fp_dup(UNIXCB(skb).fp);
+ } else
+ __skb_queue_head(&peek_stack, skb);
+ } while (size);
- /* put message back and return */
+ /* Push all peeked skbs back onto receive queue */
+ if (flags & MSG_PEEK)
+ while ((skb = __skb_dequeue(&peek_stack)))
skb_queue_head(&sk->sk_receive_queue, skb);
- break;
- }
- } while (size);
mutex_unlock(&u->readlock);
scm_recv(sock, msg, siocb->scm, flags);
--
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