From: David Miller <[email protected]>
Date: Tue, 05 Jun 2007 00:02:47 -0700 (PDT)
> From: Miklos Szeredi <[email protected]>
> Date: Mon, 04 Jun 2007 11:45:32 +0200
>
> > > A recv() on an AF_UNIX, SOCK_STREAM socket can race with a
> > > send()+close() on the peer, causing recv() to return zero, even though
> > > the sent data should be received.
> > >
> > > This happens if the send() and the close() is performed between
> > > skb_dequeue() and checking sk->sk_shutdown in unix_stream_recvmsg():
> > >
> > > process A skb_dequeue() returns NULL, there's no data in the socket queue
> > > process B new data is inserted onto the queue by unix_stream_sendmsg()
> > > process B sk->sk_shutdown is set to SHUTDOWN_MASK by unix_release_sock()
> > > process A sk->sk_shutdown is checked, unix_release_sock() returns zero
> >
> > This is only part of the story. It turns out, there are other races
> > involving the garbage collector, that can throw away perfectly good
> > packets with AF_UNIX sockets in them.
> >
> > The problems arise when a socket goes from installed to in-flight or
> > vica versa during garbage collection. Since gc is done with a
> > spinlock held, this only shows up on SMP.
> >
> > The following patch fixes it for me, but it's possibly the wrong
> > approach.
> >
> > Signed-off-by: Miklos Szeredi <[email protected]>
Concerning this specific patch I think we need to rethink it
a bit.
Holding a global mutex over recvmsg() calls under AF_UNIX is pretty
much a non-starter, this will kill performance for multi-threaded
apps.
One possible solution is for the garbage collection code to hold the
u->readlock while processing a socket, but be careful about deadlocks.
Anyone want to give that a try?
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Stuff]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
[Linux Resources]
