proc: Fix Oops on stat of /proc/<zombie pid>/ns/net

Don't call iput with the inode half setup to be a namespace filedescriptor.
Instead rearrange the code so that we don't initialize ei->ns_ops until
after I ns_ops->get succeeds, preventing us from invoking ns_ops->put
when ns_ops->get failed.

Reported-by: Ingo Saitz <Ingo.Saitz@stud.uni-hannover.de>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

1 files changed, 6 insertions, 3 deletions

diff --git a/fs/proc/namespaces.c b/fs/proc/namespaces.c
index 781dec5bd68..be177f702ac 100644
--- a/fs/proc/namespaces.c
+++ b/fs/proc/namespaces.c
@@ -38,18 +38,21 @@ static struct dentry *proc_ns_instantiate(struct inode *dir,
         struct inode *inode;
         struct proc_inode *ei;
         struct dentry *error = ERR_PTR(-ENOENT);
+        void *ns;
 
         inode = proc_pid_make_inode(dir->i_sb, task);
         if (!inode)
                 goto out;
 
+        ns = ns_ops->get(task);
+        if (!ns)
+                goto out_iput;
+
         ei = PROC_I(inode);
         inode->i_mode = S_IFREG|S_IRUSR;
         inode->i_fop  = &ns_file_operations;
         ei->ns_ops    = ns_ops;
-        ei->ns        = ns_ops->get(task);
-        if (!ei->ns)
-                goto out_iput;
+        ei->ns        = ns;
 
         dentry->d_op = &pid_dentry_operations;
         d_add(dentry, inode);