[patch 23/36] UNIX: EOF on non-blocking SOCK_SEQPACKET

Greg KH
2007-12-13T06:45:53Z

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2.6.22-stable review patch. If anyone has any objections, please let us
know.

------------------
From: Florian Zumbiehl <florz@florz.de>

[UNIX]: EOF on non-blocking SOCK_SEQPACKET

[ Upstream commit: 0a11225887fe6cbccd882404dc36ddc50f47daf9 ]

I am not absolutely sure whether this actually is a bug (as in: I've got
no clue what the standards say or what other implementations do), but at
least I was pretty surprised when I noticed that a recv() on a
non-blocking unix domain socket of type SOCK_SEQPACKET (which is connection
oriented, after all) where the remote end has closed the connection
returned -1 (EAGAIN) rather than 0 to indicate end of file.

This is a test case:

| #include <sys/types.h>
| #include <unistd.h>
| #include <sys/socket.h>
| #include <sys/un.h>
| #include <fcntl.h>
| #include <string.h>
| #include <stdlib.h>
|
| int main(){
| int sock;
| struct sockaddr_un addr;
| char buf[4096];
| int pfds[2];
|
| pipe(pfds);
| sock=socket(PF_UNIX,SOCK_SEQPACKET,0);
| addr.sun_family=AF_UNIX;
| strcpy(addr.sun_path,"/tmp/foobar_testsock");
| bind(sock,(struct sockaddr *)&addr,sizeof(addr));
| listen(sock,1);
| if(fork()){
| close(sock);
| sock=socket(PF_UNIX,SOCK_SEQPACKET,0);
| connect(sock,(struct sockaddr *)&addr,sizeof(addr));
| fcntl(sock,F_SETFL,fcntl(sock,F_GETFL)|O_NONBLOCK);
| close(pfds[1]);
| read(pfds[0],buf,sizeof(buf));
| recv(sock,buf,sizeof(buf),0); // <-- this one
| }else accept(sock,NULL,NULL);
| exit(0);
| }

If you try it, make sure /tmp/foobar_testsock doesn't exist.

The marked recv() returns -1 (EAGAIN) on 2.6.23.9. Below you find a
patch that fixes that.

Signed-off-by: Florian Zumbiehl <florz@florz.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
net/unix/af_unix.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

--- a/net/unix/af_unix.c
+++ b/net/unix/af_unix.c
@@ -1608,8 +1608,15 @@ static int unix_dgram_recvmsg(struct kio
mutex_lock(&u->readlock);

skb = skb_recv_datagram(sk, flags, noblock, &err);
- if (!skb)
+ if (!skb) {
+ unix_state_lock(sk);
+ /* Signal EOF on disconnected non-blocking SEQPACKET socket. */
+ if (sk->sk_type == SOCK_SEQPACKET && err == -EAGAIN &&
+ (sk->sk_shutdown & RCV_SHUTDOWN))
+ err = 0;
+ unix_state_unlock(sk);
goto out_unlock;
+ }

wake_up_interruptible(&u->peer_wait);

--