sysfs tries to keep dcache a strict subset of sysfs_dirent tree by
shooting down dentries when a node is removed, that is, no negative
dentry for sysfs.  However, the lookup function returned NULL and thus
created negative dentries when the target node didn't exist.

Make sysfs_lookup() return ERR_PTR(-ENOENT) on lookup failure.  This
fixes the NULL dereference bug in sysfs_get_dentry() discovered by
bluetooth rfcomm device moving around.

Signed-off-by: Tejun Heo <htejun@gmail.com>
---
 fs/sysfs/dir.c |    4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

Index: work/fs/sysfs/dir.c
===================================================================
--- work.orig/fs/sysfs/dir.c
+++ work/fs/sysfs/dir.c
@@ -678,8 +678,10 @@ static struct dentry * sysfs_lookup(stru
 	sd = sysfs_find_dirent(parent_sd, dentry->d_name.name);
 
 	/* no such entry */
-	if (!sd)
+	if (!sd) {
+		ret = ERR_PTR(-ENOENT);
 		goto out_unlock;
+	}
 
 	/* attach dentry and inode */
 	inode = sysfs_get_inode(sd);
--
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