Fix race between proc_get_inode() and remove_proc_entry()

proc_lookup				remove_proc_entry
===========				=================

lock_kernel();
spin_lock(&proc_subdir_lock);
[find PDE with refcount 0]
spin_unlock(&proc_subdir_lock);
					spin_lock(&proc_subdir_lock);
					[find PDE with refcount 0]
					[check refcount and free PDE]
					spin_unlock(&proc_subdir_lock);
proc_get_inode:
	de_get(de); /* boom */

Signed-off-by: Alexey Dobriyan <adobriyan@openvz.org>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Oleg Nesterov <oleg@tv-sign.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 0 deletions

diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index f4f7a63cae1f..3469f96bc8b2 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h
@@ -106,6 +106,9 @@ int task_statm(struct mm_struct *, int *, int *, int *, int *);
 char *task_mem(struct mm_struct *, char *);
 void clear_refs_smap(struct mm_struct *mm);
 
+struct proc_dir_entry *de_get(struct proc_dir_entry *de);
+void de_put(struct proc_dir_entry *de);
+
 extern struct proc_dir_entry *create_proc_entry(const char *name, mode_t mode,
                                                 struct proc_dir_entry *parent);
 extern void remove_proc_entry(const char *name, struct proc_dir_entry *parent);