tree fcc32d8ac71aa67dba344a8a71114a49ee9430d0
parent 072ee0143048a6bbd4068002352a4201ac853b6e
author Nick Kralevich <nnk@google.com> 1366155692 -0700
committer Nick Kralevich <nnk@google.com> 1366818806 -0700

fs_mgr: make block devices read-only

When a filesystem is mounted read-only, make the underlying
block device read-only too. This helps prevent an attacker
who is able to change permissions on the files in /dev
(for example, symlink attack) from modifying the block device.

In particular, this change would have stopped the LG Thrill / Optimus
3D rooting exploit
(http://vulnfactory.org/blog/2012/02/26/rooting-the-lg-thrill-optimus-3d/)
as that exploit modified the raw block device corresponding to /system.

This change also makes UID=0 less powerful. Block devices cannot
be made writable again without CAP_SYS_ADMIN, so an escalation
to UID=0 by itself doesn't give full root access.

adb/mount: Prior to mounting something read-write, remove the
read-only restrictions on the underlying block device. This avoids
messing up developer workflows.

Change-Id: I135098a8fe06f327336f045aab0d48ed9de33807