[PATCH] check for null vfsmount in dentry_open()

Make sure no-one calls dentry_open with a NULL vfsmount argument and crap
out with a stacktrace otherwise.  A NULL file->f_vfsmnt has always been
problematic, but with the per-mount r/o tracking we can't accept anymore
at all.

[AV] the last place that passed NULL had been eliminated by the previous
patch (reiserfs xattr stuff)

Acked-by: Al Viro <viro@ZenIV.linux.org.uk>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Hansen <haveblue@us.ibm.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

1 files changed, 12 insertions, 0 deletions

diff --git a/fs/open.c b/fs/open.c
index 54198538b67e..a4b12022edaa 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -903,6 +903,18 @@ struct file *dentry_open(struct dentry *dentry, struct vfsmount *mnt, int flags)
         int error;
         struct file *f;
 
+        /*
+         * We must always pass in a valid mount pointer.   Historically
+         * callers got away with not passing it, but we must enforce this at
+         * the earliest possible point now to avoid strange problems deep in the
+         * filesystem stack.
+         */
+        if (!mnt) {
+                printk(KERN_WARNING "%s called with NULL vfsmount\n", __func__);
+                dump_stack();
+                return ERR_PTR(-EINVAL);
+        }
+
         error = -ENFILE;
         f = get_empty_filp();
         if (f == NULL) {