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.

Acked-by: Al Viro <[EMAIL PROTECTED]>
Signed-off-by: Christoph Hellwig <[EMAIL PROTECTED]>
Signed-off-by: Dave Hansen <[EMAIL PROTECTED]>
---

 linux-2.6.git-dave/fs/open.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)

diff -puN fs/open.c~check-for-NULL-vfsmount-in-dentry-open fs/open.c
--- linux-2.6.git/fs/open.c~check-for-NULL-vfsmount-in-dentry-open      
2008-02-15 13:25:42.000000000 -0800
+++ linux-2.6.git-dave/fs/open.c        2008-02-15 13:25:42.000000000 -0800
@@ -903,6 +903,18 @@ struct file *dentry_open(struct dentry *
        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) {
_
--
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