[ 057/218] fs/proc: fix potential unregister_sysctl_table hang

From: Greg Kroah-Hartman
Date: Fri Sep 28 2012 - 17:48:41 EST


3.4-stable review patch. If anyone has any objections, please let me know.

------------------

From: Francesco Ruggeri <fruggeri@xxxxxxxxxxxxxxxxxx>

commit 6bf6104573482570f7103d3e5ddf9574db43a363 upstream.

The unregister_sysctl_table() function hangs if all references to its
ctl_table_header structure are not dropped.

This can happen sometimes because of a leak in proc_sys_lookup():
proc_sys_lookup() gets a reference to the table via lookup_entry(), but
it does not release it when a subsequent call to sysctl_follow_link()
fails.

This patch fixes this leak by making sure the reference is always
dropped on return.

See also commit 076c3eed2c31 ("sysctl: Rewrite proc_sys_lookup
introducing find_entry and lookup_entry") which reorganized this code in
3.4.

Tested in Linux 3.4.4.

Signed-off-by: Francesco Ruggeri <fruggeri@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
fs/proc/proc_sysctl.c | 5 ++---
1 file changed, 2 insertions(+), 3 deletions(-)

--- a/fs/proc/proc_sysctl.c
+++ b/fs/proc/proc_sysctl.c
@@ -462,9 +462,6 @@ static struct dentry *proc_sys_lookup(st

err = ERR_PTR(-ENOMEM);
inode = proc_sys_make_inode(dir->i_sb, h ? h : head, p);
- if (h)
- sysctl_head_finish(h);
-
if (!inode)
goto out;

@@ -473,6 +470,8 @@ static struct dentry *proc_sys_lookup(st
d_add(dentry, inode);

out:
+ if (h)
+ sysctl_head_finish(h);
sysctl_head_finish(head);
return err;
}


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