proc: Use nd_jump_link in proc_ns_follow_link

Update proc_ns_follow_link to use nd_jump_link instead of just
manually updating nd.path.dentry.

This fixes the BUG_ON(nd->inode != parent->d_inode) reported by Dave
Jones and reproduced trivially with mkdir /proc/self/ns/uts/a.

Sigh it looks like the VFS change to require use of nd_jump_link
happend while proc_ns_follow_link was baking and since the common case
of proc_ns_follow_link continued to work without problems the need for
making this change was overlooked.

Cc: stable@vger.kernel.org
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>

1 files changed, 6 insertions, 6 deletions

diff --git a/fs/proc/namespaces.c b/fs/proc/namespaces.c
index b7a47196c8c3..66b51c0383da 100644
--- a/fs/proc/namespaces.c
+++ b/fs/proc/namespaces.c
@@ -118,7 +118,7 @@ static void *proc_ns_follow_link(struct dentry *dentry, struct nameidata *nd)
         struct super_block *sb = inode->i_sb;
         struct proc_inode *ei = PROC_I(inode);
         struct task_struct *task;
-        struct dentry *ns_dentry;
+        struct path ns_path;
         void *error = ERR_PTR(-EACCES);
 
         task = get_proc_task(inode);
@@ -128,14 +128,14 @@ static void *proc_ns_follow_link(struct dentry *dentry, struct nameidata *nd)
         if (!ptrace_may_access(task, PTRACE_MODE_READ))
                 goto out_put_task;
 
-        ns_dentry = proc_ns_get_dentry(sb, task, ei->ns_ops);
-        if (IS_ERR(ns_dentry)) {
-                error = ERR_CAST(ns_dentry);
+        ns_path.dentry = proc_ns_get_dentry(sb, task, ei->ns_ops);
+        if (IS_ERR(ns_path.dentry)) {
+                error = ERR_CAST(ns_path.dentry);
                 goto out_put_task;
         }
 
-        dput(nd->path.dentry);
-        nd->path.dentry = ns_dentry;
+        ns_path.mnt = mntget(nd->path.mnt);
+        nd_jump_link(nd, &ns_path);
         error = NULL;
 
 out_put_task: