proc 2/2: remove struct proc_dir_entry::owner

Setting ->owner as done currently (pde->owner = THIS_MODULE) is racy
as correctly noted at bug #12454. Someone can lookup entry with NULL
->owner, thus not pinning enything, and release it later resulting
in module refcount underflow.

We can keep ->owner and supply it at registration time like ->proc_fops
and ->data.

But this leaves ->owner as easy-manipulative field (just one C assignment)
and somebody will forget to unpin previous/pin current module when
switching ->owner. ->proc_fops is declared as "const" which should give
some thoughts.

->read_proc/->write_proc were just fixed to not require ->owner for
protection.

rmmod'ed directories will be empty and return "." and ".." -- no harm.
And directories with tricky enough readdir and lookup shouldn't be modular.
We definitely don't want such modular code.

Removing ->owner will also make PDE smaller.

So, let's nuke it.

Kudos to Jeff Layton for reminding about this, let's say, oversight.

http://bugzilla.kernel.org/show_bug.cgi?id=12454

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>

1 files changed, 2 insertions, 6 deletions

diff --git a/net/sctp/protocol.c b/net/sctp/protocol.c
index cb198af8887c..8eb3e61cb701 100644
--- a/net/sctp/protocol.c
+++ b/net/sctp/protocol.c
@@ -106,12 +106,8 @@ static __init int sctp_proc_init(void)
                 goto out_nomem;
 #ifdef CONFIG_PROC_FS
         if (!proc_net_sctp) {
-                struct proc_dir_entry *ent;
-                ent = proc_mkdir("sctp", init_net.proc_net);
-                if (ent) {
-                        ent->owner = THIS_MODULE;
-                        proc_net_sctp = ent;
-                } else
+                proc_net_sctp = proc_mkdir("sctp", init_net.proc_net);
+                if (!proc_net_sctp)
                         goto out_free_percpu;
         }