[RFC][PATCH 03/30] check for null vfsmount in dentry_open()

[Dave Hansen]

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.

Signed-off-by: Christoph Hellwig <hch@xxxxxx>
Signed-off-by: Dave Hansen <haveblue@xxxxxxxxxx>
---

 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	2008-02-08 13:04:45.000000000 -0800
+++ linux-2.6.git-dave/fs/open.c	2008-02-08 13:04:45.000000000 -0800
@@ -906,6 +906,18 @@ 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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