SELinux: call cap_file_mmap in selinux_file_mmap

Currently SELinux does not check CAP_SYS_RAWIO in the file_mmap hook.  This
means there is no DAC check on the ability to mmap low addresses in the
memory space.  This function adds the DAC check for CAP_SYS_RAWIO while
maintaining the selinux check on mmap_zero.  This means that processes
which need to mmap low memory will need CAP_SYS_RAWIO and mmap_zero but will
NOT need the SELinux sys_rawio capability.

Signed-off-by: Eric Paris <eparis@redhat.com>
Signed-off-by: James Morris <jmorris@namei.org>

1 files changed, 13 insertions, 1 deletions

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 1e8cfc4c2ed6..e6d1432b0800 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -3030,9 +3030,21 @@ static int selinux_file_mmap(struct file *file, unsigned long reqprot,
         int rc = 0;
         u32 sid = current_sid();
 
-        if (addr < mmap_min_addr)
+        /*
+         * notice that we are intentionally putting the SELinux check before
+         * the secondary cap_file_mmap check.  This is such a likely attempt
+         * at bad behaviour/exploit that we always want to get the AVC, even
+         * if DAC would have also denied the operation.
+         */
+        if (addr < mmap_min_addr) {
                 rc = avc_has_perm(sid, sid, SECCLASS_MEMPROTECT,
                                   MEMPROTECT__MMAP_ZERO, NULL);
+                if (rc)
+                        return rc;
+        }
+
+        /* do DAC check on address space usage */
+        rc = cap_file_mmap(file, reqprot, prot, flags, addr, addr_only);
         if (rc || addr_only)
                 return rc;