procfs: fix race between symlink removals and traversals

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>

diff --git a/fs/proc/generic.c b/fs/proc/generic.c
index a2596afffae6dad430f8cb2727628e162c567876..846b1d7852ed25cb376ae30ad7defcdd5878bd7f 100644 (file)
--- 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>
@@ -163,17 +162,6 @@ 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,
-};
-
 /*
  * As some entries in /proc are volatile, we want to 
  * get rid of unused dentries.  This could be made 

diff --git a/fs/proc/inode.c b/fs/proc/inode.c
index 073aea60cf8f0ed1ccce604ab0accd8b07dd96ba..843b8ef04e84bf1352d050da0470ddd3744fe67a 100644 (file)
--- 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>
 
@@ -373,6 +374,26 @@ static const struct file_operations proc_reg_file_ops_no_compat = {
 };
 #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);

diff --git a/fs/proc/internal.h b/fs/proc/internal.h
index d600fb098b6ad3ad51d227709d43161d8a9d0abc..ec335ef625334b44c730e83dda81ec3b57ceb129 100644 (file)
--- a/fs/proc/internal.h
+++ b/fs/proc/internal.h
@@ -202,6 +202,7 @@ 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;