make default ->i_fop have ->open() fail with ENXIO

As it is, default ->i_fop has NULL ->open() (along with all other methods).
The only case where it matters is reopening (via procfs symlink) a file that
didn't get its ->f_op from ->i_fop - anything else will have ->i_fop assigned
to something sane (default would fail on read/write/ioctl/etc.).

	Unfortunately, such case exists - alloc_file() users, especially
anon_get_file() ones.  There we have tons of opened files of very different
kinds sharing the same inode.  As the result, attempt to reopen those via
procfs succeeds and you get a descriptor you can't do anything with.

	Moreover, in case of sockets we set ->i_fop that will only be used
on such reopen attempts - and put a failing ->open() into it to make sure
those do not succeed.

	It would be simpler to put such ->open() into default ->i_fop and leave
it unchanged both for anon inode (as we do anyway) and for socket ones.  Result:
	* everything going through do_dentry_open() works as it used to
	* sock_no_open() kludge is gone
	* attempts to reopen anon-inode files fail as they really ought to
	* ditto for aio_private_file()
	* ditto for perfmon - this one actually tried to imitate sock_no_open()
trick, but failed to set ->i_fop, so in the current tree reopens succeed and
yield completely useless descriptor.  Intent clearly had been to fail with
-ENXIO on such reopens; now it actually does.
	* everything else that used alloc_file() keeps working - it has ->i_fop
set for its inodes anyway

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 0 insertions, 19 deletions

diff --git a/net/socket.c b/net/socket.c
index fe20c319a0bb..850f6c383342 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -113,7 +113,6 @@ unsigned int sysctl_net_busy_read __read_mostly;
 unsigned int sysctl_net_busy_poll __read_mostly;
 #endif
 
-static int sock_no_open(struct inode *irrelevant, struct file *dontcare);
 static ssize_t sock_aio_read(struct kiocb *iocb, const struct iovec *iov,
 			 unsigned long nr_segs, loff_t pos);
 static ssize_t sock_aio_write(struct kiocb *iocb, const struct iovec *iov,
@@ -151,7 +150,6 @@ static const struct file_operations socket_file_ops = {
 	.compat_ioctl = compat_sock_ioctl,
 #endif
 	.mmap =		sock_mmap,
-	.open =		sock_no_open,	/* special open code to disallow open via /proc */
 	.release =	sock_close,
 	.fasync =	sock_fasync,
 	.sendpage =	sock_sendpage,
@@ -559,23 +557,6 @@ static struct socket *sock_alloc(void)
 	return sock;
 }
 
-/*
- *	In theory you can't get an open on this inode, but /proc provides
- *	a back door. Remember to keep it shut otherwise you'll let the
- *	creepy crawlies in.
- */
-
-static int sock_no_open(struct inode *irrelevant, struct file *dontcare)
-{
-	return -ENXIO;
-}
-
-const struct file_operations bad_sock_fops = {
-	.owner = THIS_MODULE,
-	.open = sock_no_open,
-	.llseek = noop_llseek,
-};
-
 /**
  *	sock_release	-	close a socket
  *	@sock: socket to close