Driver-Core: devtmpfs - reset inode permissions before unlinking

commit 5e31d76f upstream.

Before unlinking the inode, reset the current permissions of possible
references like hardlinks, so granted permissions can not be retained
across the device lifetime by creating hardlinks, in the unusual case
that there is a user-writable directory on the same filesystem.
Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/base/devtmpfs.c

@@ -295,6 +295,19 @@ int devtmpfs_delete_node(struct device *dev)
 		if (dentry->d_inode) {
 			err = vfs_getattr(nd.path.mnt, dentry, &stat);
 			if (!err && dev_mynode(dev, dentry->d_inode, &stat)) {
+				struct iattr newattrs;
+				/*
+				 * before unlinking this node, reset permissions
+				 * of possible references like hardlinks
+				 */
+				newattrs.ia_uid = 0;
+				newattrs.ia_gid = 0;
+				newattrs.ia_mode = stat.mode & ~0777;
+				newattrs.ia_valid =
+					ATTR_UID|ATTR_GID|ATTR_MODE;
+				mutex_lock(&dentry->d_inode->i_mutex);
+				notify_change(dentry, &newattrs);
+				mutex_unlock(&dentry->d_inode->i_mutex);
 				err = vfs_unlink(nd.path.dentry->d_inode,
 						 dentry);
 				if (!err || err == -ENOENT)