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>

2 files changed, 0 insertions, 6 deletions

diff --git a/net/can/bcm.c b/net/can/bcm.c
index b7c7d46..95d7f32 100644
--- a/net/can/bcm.c
+++ b/net/can/bcm.c
@@ -1604,10 +1604,6 @@ static int __init bcm_module_init(void)
 
 	/* create /proc/net/can-bcm directory */
 	proc_dir = proc_mkdir("can-bcm", init_net.proc_net);
-
-	if (proc_dir)
-		proc_dir->owner = THIS_MODULE;
-
 	return 0;
 }
 
diff --git a/net/can/proc.c b/net/can/proc.c
index 520fef5..1463653 100644
--- a/net/can/proc.c
+++ b/net/can/proc.c
@@ -473,8 +473,6 @@ void can_init_proc(void)
 		return;
 	}
 
-	can_dir->owner = THIS_MODULE;
-
 	/* own procfs entries from the AF_CAN core */
 	pde_version     = can_create_proc_readentry(CAN_PROC_VERSION, 0644,
 					can_proc_read_version, NULL);