Documentation,selinux: deprecate setting checkreqprot to 1

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 <sds@tycho.nsa.gov>
Signed-off-by: Paul Moore <paul@paul-moore.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index b33cf155cc48..d7762264f262 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -142,8 +142,11 @@ static int __init checkreqprot_setup(char *str)
 {
 	unsigned long checkreqprot;
 
-	if (!kstrtoul(str, 0, &checkreqprot))
+	if (!kstrtoul(str, 0, &checkreqprot)) {
 		selinux_checkreqprot_boot = checkreqprot ? 1 : 0;
+		if (checkreqprot)
+			pr_warn("SELinux: checkreqprot set to 1 via kernel parameter.  This is deprecated and will be rejected in a future kernel release.\n");
+	}
 	return 1;
 }
 __setup("checkreqprot=", checkreqprot_setup);