[PATCH 2/2] SELinux: selinux_file_mmap always enforce mapping the 0page

[Eric Paris]

Currently SELinux enforcement of controls on the ability to map the 0 page
is determined by the mmap_min_addr tunable.  This patch causes SELinux to
ignore the tunable and to always (but ONLY) protect the 0 page.

The tunable will now only control the need for CAP_SYS_RAWIO and SELinux
permissions will always protect the 0 page based on it's mmap_zero
permission.

This allows users who need to disable the mmap_min_addr controls (usual reason
being they run WINE as a non-root user) to do so and still have SELinux
controls preventing confined domains (like a web server) from being able to
map the 0 page.

Note: the additional SELinux restriction will now ONLY protect the 0 page.
CAP_SYS_RAWIO will protect anything between 0 and mmap_min_addr, but SELinux
will only protect between 0 and PAGE_SIZE.

Signed-off-by: Eric Paris <eparis@xxxxxxxxxx>
---

 include/linux/security.h |    1 -
 security/selinux/hooks.c |    2 +-
 2 files changed, 1 insertions(+), 2 deletions(-)

diff --git a/include/linux/security.h b/include/linux/security.h
index f7d198a..de774f7 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -91,7 +91,6 @@ struct seq_file;
 extern int cap_netlink_send(struct sock *sk, struct sk_buff *skb);
 extern int cap_netlink_recv(struct sk_buff *skb, int cap);
 
-extern unsigned long mmap_min_addr;
 /*
  * Values used in the task_security_ops calls
  */
diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index e65677d..7bbac1d 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3034,7 +3034,7 @@ static int selinux_file_mmap(struct file *file, unsigned long reqprot,
 	int rc = 0;
 	u32 sid = current_sid();
 
-	if (addr < mmap_min_addr)
+	if (addr < PAGE_SIZE)
 		rc = avc_has_perm(sid, sid, SECCLASS_MEMPROTECT,
 				  MEMPROTECT__MMAP_ZERO, NULL);
 	if (rc || addr_only)

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