On Wed, Jan 8, 2020 at 11:24 AM Stephen Smalley [off-list ref] wrote:

Deprecate setting the SELinux checkreqprot tunable to 1 via kernel
parameter or /sys/fs/selinux/checkreqprot.  Setting it to 0 is left
intact for compatibility since Android and some Linux distributions
do so for security and treat an inability to set it as a fatal error.
Eventually setting it to 0 will become a no-op and the kernel will
stop using checkreqprot's value internally altogether.

checkreqprot was originally introduced as a compatibility mechanism
for legacy userspace and the READ_IMPLIES_EXEC personality flag.
However, if set to 1, it weakens security by allowing mappings to be
made executable without authorization by policy.  The default value
for the SECURITY_SELINUX_CHECKREQPROT_VALUE config option was changed
from 1 to 0 in commit 2a35d196c160e3 ("selinux: change
CONFIG_SECURITY_SELINUX_CHECKREQPROT_VALUE default") and both Android
and Linux distributions began explicitly setting
/sys/fs/selinux/checkreqprot to 0 some time ago.

Signed-off-by: Stephen Smalley <redacted>
---
 .../ABI/obsolete/sysfs-selinux-checkreqprot   | 23 +++++++++++++++++++
 .../admin-guide/kernel-parameters.txt         |  1 +
 MAINTAINERS                                   |  1 +
 security/selinux/Kconfig                      |  3 +++
 security/selinux/hooks.c                      |  5 +++-
 security/selinux/selinuxfs.c                  |  8 +++++++
 6 files changed, 40 insertions(+), 1 deletion(-)
 create mode 100644 Documentation/ABI/obsolete/sysfs-selinux-checkreqprot

I think this looks fine, but considering this week was the first time
we really discussed this, let's hold off until after the next merge
window so we get a full cycle in linux-next for folks to complain :)

-- 
paul moore
www.paul-moore.com