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

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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>
This commit is contained in:
Al Viro
2014-11-18 23:38:21 -05:00
parent 1f55a6ec94
commit bd9b51e79c
6 changed files with 8 additions and 61 deletions
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10
arch/ia64/kernel/perfmon.c
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@@ -2145,22 +2145,12 @@ doit:
return 0;
}
static int
pfm_no_open(struct inode *irrelevant, struct file *dontcare)
{
DPRINT(("pfm_no_open called\n"));
return -ENXIO;
}
static const struct file_operations pfm_file_ops = {
.llseek = no_llseek,
.read = pfm_read,
.write = pfm_write,
.poll = pfm_poll,
.unlocked_ioctl = pfm_ioctl,
.open = pfm_no_open, /* special open code to disallow open via /proc */
.fasync = pfm_fasync,
.release = pfm_close,
.flush = pfm_flush