From d3381fab77cbca6f9664cf49b3f5dd3171f1f6d3 Mon Sep 17 00:00:00 2001 From: "Eric W. Biederman" Date: Wed, 1 Feb 2017 06:06:16 +1300 Subject: fs: Better permission checking for submounts commit 93faccbbfa958a9668d3ab4e30f38dd205cee8d8 upstream. To support unprivileged users mounting filesystems two permission checks have to be performed: a test to see if the user allowed to create a mount in the mount namespace, and a test to see if the user is allowed to access the specified filesystem. The automount case is special in that mounting the original filesystem grants permission to mount the sub-filesystems, to any user who happens to stumble across the their mountpoint and satisfies the ordinary filesystem permission checks. Attempting to handle the automount case by using override_creds almost works. It preserves the idea that permission to mount the original filesystem is permission to mount the sub-filesystem. Unfortunately using override_creds messes up the filesystems ordinary permission checks. Solve this by being explicit that a mount is a submount by introducing vfs_submount, and using it where appropriate. vfs_submount uses a new mount internal mount flags MS_SUBMOUNT, to let sget and friends know that a mount is a submount so they can take appropriate action. sget and sget_userns are modified to not perform any permission checks on submounts. follow_automount is modified to stop using override_creds as that has proven problemantic. do_mount is modified to always remove the new MS_SUBMOUNT flag so that we know userspace will never by able to specify it. autofs4 is modified to stop using current_real_cred that was put in there to handle the previous version of submount permission checking. cifs is modified to pass the mountpoint all of the way down to vfs_submount. debugfs is modified to pass the mountpoint all of the way down to trace_automount by adding a new parameter. To make this change easier a new typedef debugfs_automount_t is introduced to capture the type of the debugfs automount function. Fixes: 069d5ac9ae0d ("autofs: Fix automounts by using current_real_cred()->uid") Fixes: aeaa4a79ff6a ("fs: Call d_automount with the filesystems creds") Reviewed-by: Trond Myklebust Reviewed-by: Seth Forshee Signed-off-by: "Eric W. Biederman" Signed-off-by: Greg Kroah-Hartman --- fs/nfs/namespace.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'fs/nfs/namespace.c') diff --git a/fs/nfs/namespace.c b/fs/nfs/namespace.c index 5551e8ef67fd..e49d831c4e85 100644 --- a/fs/nfs/namespace.c +++ b/fs/nfs/namespace.c @@ -226,7 +226,7 @@ static struct vfsmount *nfs_do_clone_mount(struct nfs_server *server, const char *devname, struct nfs_clone_mount *mountdata) { - return vfs_kern_mount(&nfs_xdev_fs_type, 0, devname, mountdata); + return vfs_submount(mountdata->dentry, &nfs_xdev_fs_type, devname, mountdata); } /** -- cgit v1.2.3