[PATCH 3.19 100/177] procfs: fix race between symlink removals and traversals

Greg Kroah-Hartman
2015-03-16T14:15:27Z

From: Al Viro <viro@zeniv.linux.org.uk>

commit 7e0e953bb0cf649f93277ac8fb67ecbb7f7b04a9 upstream.

use_pde()/unuse_pde() in ->follow_link()/->put_link() resp.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/proc/generic.c | 12 ------------
fs/proc/inode.c | 21 +++++++++++++++++++++
fs/proc/internal.h | 1 +
3 files changed, 22 insertions(+), 12 deletions(-)

--- a/fs/proc/generic.c
+++ b/fs/proc/generic.c
@@ -19,7 +19,6 @@
#include <linux/mount.h>
#include <linux/init.h>
#include <linux/idr.h>
-#include <linux/namei.h>
#include <linux/bitops.h>
#include <linux/spinlock.h>
#include <linux/completion.h>
@@ -223,17 +222,6 @@ void proc_free_inum(unsigned int inum)
spin_unlock_irqrestore(&proc_inum_lock, flags);
}

-static void *proc_follow_link(struct dentry *dentry, struct nameidata *nd)
-{
- nd_set_link(nd, __PDE_DATA(dentry->d_inode));
- return NULL;
-}
-
-static const struct inode_operations proc_link_inode_operations = {
- .readlink = generic_readlink,
- .follow_link = proc_follow_link,
-};
-
/*
* Don't create negative dentries here, return -ENOENT by hand
* instead.
--- a/fs/proc/inode.c
+++ b/fs/proc/inode.c
@@ -23,6 +23,7 @@
#include <linux/slab.h>
#include <linux/mount.h>
#include <linux/magic.h>
+#include <linux/namei.h>

#include <asm/uaccess.h>

@@ -393,6 +394,26 @@ static const struct file_operations proc
};
#endif

+static void *proc_follow_link(struct dentry *dentry, struct nameidata *nd)
+{
+ struct proc_dir_entry *pde = PDE(dentry->d_inode);
+ if (unlikely(!use_pde(pde)))
+ return ERR_PTR(-EINVAL);
+ nd_set_link(nd, pde->data);
+ return pde;
+}
+
+static void proc_put_link(struct dentry *dentry, struct nameidata *nd, void *p)
+{
+ unuse_pde(p);
+}
+
+const struct inode_operations proc_link_inode_operations = {
+ .readlink = generic_readlink,
+ .follow_link = proc_follow_link,
+ .put_link = proc_put_link,
+};
+
struct inode *proc_get_inode(struct super_block *sb, struct proc_dir_entry *de)
{
struct inode *inode = new_inode_pseudo(sb);
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -200,6 +200,7 @@ struct pde_opener {
int closing;
struct completion *c;
};
+extern const struct inode_operations proc_link_inode_operations;

extern const struct inode_operations proc_pid_link_inode_operations;