Commit bc6155d1 authored Sep 18, 2017 by Eric W. Biederman

fs: Allow superblock owner to access do_remount_sb()



Superblock level remounts are currently restricted to global
CAP_SYS_ADMIN, as is the path for changing the root mount to
read only on umount. Loosen both of these permission checks to
also allow CAP_SYS_ADMIN in any namespace which is privileged
towards the userns which originally mounted the filesystem.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Acked-by: Serge Hallyn <serge@hallyn.com>
Acked-by: Christian Brauner <christian@brauner.io>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

parent 0031181c

fs/namespace.c

+2 −2

Original line number	Diff line number	Diff line
		@@ -1590,7 +1590,7 @@ static int do_umount(struct mount *mnt, int flags)
		* Special case for "unmounting" root ...
		* we just try to remount it readonly.
		*/
		if (!capable(CAP_SYS_ADMIN))
		if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN))
		return -EPERM;
		down_write(&sb->s_umount);
		if (!sb_rdonly(sb))
		@@ -2333,7 +2333,7 @@ static int do_remount(struct path *path, int ms_flags, int sb_flags,
		down_write(&sb->s_umount);
		if (ms_flags & MS_BIND)
		err = change_mount_flags(path->mnt, ms_flags);
		else if (!capable(CAP_SYS_ADMIN))
		else if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN))
		err = -EPERM;
		else
		err = do_remount_sb(sb, sb_flags, data, 0);