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@xxxxxxxxxxxxx>
---
.../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
diff --git a/Documentation/ABI/obsolete/sysfs-selinux-checkreqprot b/Documentation/ABI/obsolete/sysfs-selinux-checkreqprot
new file mode 100644
index 000000000000..49ed9c8fd1e5
--- /dev/null
+++ b/Documentation/ABI/obsolete/sysfs-selinux-checkreqprot
@@ -0,0 +1,23 @@
+What: /sys/fs/selinux/checkreqprot
+Date: April 2005 (predates git)
+KernelVersion: 2.6.12-rc2 (predates git)
+Contact: selinux@xxxxxxxxxxxxxxx
+Description:
+
+ The selinuxfs "checkreqprot" node allows SELinux to be configured
+ to check the protection requested by userspace for mmap/mprotect
+ calls instead of the actual protection applied by the kernel.
+ This was a compatibility mechanism for legacy userspace and
+ for 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 of checkreqprot
+ at boot was changed starting in Linux v4.4 to 0 (i.e. check the
+ actual protection), and Android and Linux distributions have been
+ explicitly writing a "0" to /sys/fs/selinux/checkreqprot during
+ initialization for some time. Support for setting checkreqprot to 1
+ will be removed in a future kernel release, at which point the kernel
+ will always cease using checkreqprot internally and will always
+ check the actual protections being applied upon mmap/mprotect calls.
+ The checkreqprot selinuxfs node will remain for backward compatibility
+ but will discard writes of the "0" value and will reject writes of the
+ "1" value when this mechanism is removed.
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index eed51293d6cf..c894ddfa1393 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -512,6 +512,7 @@
Default value is set via a kernel config option.
Value can be changed at runtime via
/sys/fs/selinux/checkreqprot.
+ Setting checkreqprot to 1 is deprecated.
cio_ignore= [S390]
See Documentation/s390/common_io.rst for details.
diff --git a/MAINTAINERS b/MAINTAINERS
index 9dc5767861b5..1af5e9e8abb5 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -14807,6 +14807,7 @@ F: security/selinux/
F: scripts/selinux/
F: Documentation/admin-guide/LSM/SELinux.rst
F: Documentation/ABI/obsolete/sysfs-selinux-disable
+F: Documentation/ABI/obsolete/sysfs-selinux-checkreqprot
SENSABLE PHANTOM
M: Jiri Slaby <jirislaby@xxxxxxxxx>
diff --git a/security/selinux/Kconfig b/security/selinux/Kconfig
index 1014cb0ee956..9e921fc72538 100644
--- a/security/selinux/Kconfig
+++ b/security/selinux/Kconfig
@@ -88,6 +88,9 @@ config SECURITY_SELINUX_CHECKREQPROT_VALUE
'checkreqprot=' boot parameter. It may also be changed at runtime
via /sys/fs/selinux/checkreqprot if authorized by policy.
+ WARNING: this option is deprecated and will be removed in a future
+ kernel release.
+
If you are unsure how to answer this question, answer 0.
config SECURITY_SELINUX_SIDTAB_HASH_BITS
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 63a6e36abe9f..6777e04fd942 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);
diff --git a/security/selinux/selinuxfs.c b/security/selinux/selinuxfs.c
index 79c710911a3c..d6566adc73a6 100644
--- a/security/selinux/selinuxfs.c
+++ b/security/selinux/selinuxfs.c
@@ -668,6 +668,14 @@ static ssize_t sel_write_checkreqprot(struct file *file, const char __user *buf,
if (sscanf(page, "%u", &new_value) != 1)
goto out;
+ if (new_value) {
+ char comm[sizeof(current->comm)];
+
+ memcpy(comm, current->comm, sizeof(comm));
+ pr_warn_once("SELinux: %s (%d) set checkreqprot to 1. This is deprecated and will be rejected in a future kernel release.\n",
+ comm, current->pid);
+ }
+
fsi->state->checkreqprot = new_value ? 1 : 0;
length = count;
out:
--
2.24.1
