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authorEric W. Biederman <ebiederm@xmission.com>2017-01-31 20:06:16 +0300
committerEric W. Biederman <ebiederm@xmission.com>2017-02-01 18:36:12 +0300
commit93faccbbfa958a9668d3ab4e30f38dd205cee8d8 (patch)
treef4a102b92d86d19a52a88a57bdde19ad25250ca1 /fs/debugfs
parentc6c70f4455d1eda91065e93cc4f7eddf4499b105 (diff)
downloadlinux-93faccbbfa958a9668d3ab4e30f38dd205cee8d8.tar.xz
fs: Better permission checking for submounts
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. Cc: stable@vger.kernel.org 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 <trond.myklebust@primarydata.com> Reviewed-by: Seth Forshee <seth.forshee@canonical.com> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Diffstat (limited to 'fs/debugfs')
-rw-r--r--fs/debugfs/inode.c8
1 files changed, 4 insertions, 4 deletions
diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
index f17fcf89e18e..1e30f74a9527 100644
--- a/fs/debugfs/inode.c
+++ b/fs/debugfs/inode.c
@@ -187,9 +187,9 @@ static const struct super_operations debugfs_super_operations = {
static struct vfsmount *debugfs_automount(struct path *path)
{
- struct vfsmount *(*f)(void *);
- f = (struct vfsmount *(*)(void *))path->dentry->d_fsdata;
- return f(d_inode(path->dentry)->i_private);
+ debugfs_automount_t f;
+ f = (debugfs_automount_t)path->dentry->d_fsdata;
+ return f(path->dentry, d_inode(path->dentry)->i_private);
}
static const struct dentry_operations debugfs_dops = {
@@ -504,7 +504,7 @@ EXPORT_SYMBOL_GPL(debugfs_create_dir);
*/
struct dentry *debugfs_create_automount(const char *name,
struct dentry *parent,
- struct vfsmount *(*f)(void *),
+ debugfs_automount_t f,
void *data)
{
struct dentry *dentry = start_creating(name, parent);