[PATCH v4] selinux: Add helper functions to get and set checkreqprot

* [PATCH v4] selinux: Add helper functions to get and set checkreqprot
@ 2020-09-14 17:31 Lakshmi Ramasubramanian
  2020-09-14 17:46 ` Stephen Smalley
  2020-09-15 18:38 ` Paul Moore
  0 siblings, 2 replies; 3+ messages in thread
From: Lakshmi Ramasubramanian @ 2020-09-14 17:31 UTC (permalink / raw)
  To: stephen.smalley.work, paul; +Cc: nramas, selinux

checkreqprot data member in selinux_state struct is accessed directly by
SELinux functions to get and set. This could cause unexpected read or
write access to this data member due to compiler optimizations and/or
compiler's reordering of access to this field.

Add helper functions to get and set checkreqprot data member in
selinux_state struct. These helper functions use READ_ONCE and
WRITE_ONCE macros to ensure atomic read or write of memory for
this data member.

Signed-off-by: Lakshmi Ramasubramanian <nramas@linux.microsoft.com>
Suggested-by: Stephen Smalley <stephen.smalley.work@gmail.com>
Suggested-by: Paul Moore <paul@paul-moore.com>
---
 security/selinux/hooks.c            |  6 +++---
 security/selinux/include/security.h | 10 ++++++++++
 security/selinux/selinuxfs.c        |  5 +++--
 3 files changed, 16 insertions(+), 5 deletions(-)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 6210e98219a5..d6b182c11700 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3718,7 +3718,7 @@ static int selinux_mmap_file(struct file *file, unsigned long reqprot,
 			return rc;
 	}
 
-	if (selinux_state.checkreqprot)
+	if (checkreqprot_get(&selinux_state))
 		prot = reqprot;
 
 	return file_map_prot_check(file, prot,
@@ -3732,7 +3732,7 @@ static int selinux_file_mprotect(struct vm_area_struct *vma,
 	const struct cred *cred = current_cred();
 	u32 sid = cred_sid(cred);
 
-	if (selinux_state.checkreqprot)
+	if (checkreqprot_get(&selinux_state))
 		prot = reqprot;
 
 	if (default_noexec &&
@@ -7234,7 +7234,7 @@ static __init int selinux_init(void)
 
 	memset(&selinux_state, 0, sizeof(selinux_state));
 	enforcing_set(&selinux_state, selinux_enforcing_boot);
-	selinux_state.checkreqprot = selinux_checkreqprot_boot;
+	checkreqprot_set(&selinux_state, selinux_checkreqprot_boot);
 	selinux_avc_init(&selinux_state.avc);
 	mutex_init(&selinux_state.status_lock);
 	mutex_init(&selinux_state.policy_mutex);
diff --git a/security/selinux/include/security.h b/security/selinux/include/security.h
index 0ce2ef684ed0..3cc8bab31ea8 100644
--- a/security/selinux/include/security.h
+++ b/security/selinux/include/security.h
@@ -143,6 +143,16 @@ static inline void enforcing_set(struct selinux_state *state, bool value)
 }
 #endif
 
+static inline bool checkreqprot_get(const struct selinux_state *state)
+{
+	return READ_ONCE(state->checkreqprot);
+}
+
+static inline void checkreqprot_set(struct selinux_state *state, bool value)
+{
+	WRITE_ONCE(state->checkreqprot, value);
+}
+
 #ifdef CONFIG_SECURITY_SELINUX_DISABLE
 static inline bool selinux_disabled(struct selinux_state *state)
 {
diff --git a/security/selinux/selinuxfs.c b/security/selinux/selinuxfs.c
index 45e9efa9bf5b..4bde570d56a2 100644
--- a/security/selinux/selinuxfs.c
+++ b/security/selinux/selinuxfs.c
@@ -717,7 +717,8 @@ static ssize_t sel_read_checkreqprot(struct file *filp, char __user *buf,
 	char tmpbuf[TMPBUFLEN];
 	ssize_t length;
 
-	length = scnprintf(tmpbuf, TMPBUFLEN, "%u", fsi->state->checkreqprot);
+	length = scnprintf(tmpbuf, TMPBUFLEN, "%u",
+			   checkreqprot_get(fsi->state));
 	return simple_read_from_buffer(buf, count, ppos, tmpbuf, length);
 }
 
@@ -759,7 +760,7 @@ static ssize_t sel_write_checkreqprot(struct file *file, const char __user *buf,
 			     comm, current->pid);
 	}
 
-	fsi->state->checkreqprot = new_value ? 1 : 0;
+	checkreqprot_set(fsi->state, (new_value ? 1 : 0));
 	length = count;
 out:
 	kfree(page);
-- 
2.28.0


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