xnu-6153.11.26.tar.gz

[apple/xnu.git] / bsd / kern / ubc_subr.c

diff --git a/bsd/kern/ubc_subr.c b/bsd/kern/ubc_subr.c
index 01c615b283214cca85b56248103dcb85b5025f26..cc16291df411300a2a74ab622ed39b35ea5d4456 100644 (file)
--- a/bsd/kern/ubc_subr.c
+++ b/bsd/kern/ubc_subr.c
@@ -82,6 +82,8 @@ extern kern_return_t memory_object_pages_resident(memory_object_control_t,
 extern kern_return_t    memory_object_signed(memory_object_control_t control,
     boolean_t is_signed);
 extern boolean_t        memory_object_is_signed(memory_object_control_t);
+extern void             memory_object_mark_trusted(
+       memory_object_control_t         control);
 
 /* XXX Same for those. */
 
@@ -1937,6 +1939,33 @@ ubc_map(vnode_t vp, int flags)
                        if (vnode_ref_ext(vp, 0, VNODE_REF_FORCE)) {
                                panic("%s : VNODE_REF_FORCE failed\n", __FUNCTION__);
                        }
+                       /*
+                        * Vnodes that are on "unreliable" media (like disk
+                        * images, network filesystems, 3rd-party filesystems,
+                        * and possibly external devices) could see their
+                        * contents be changed via the backing store without
+                        * triggering copy-on-write, so we can't fully rely
+                        * on copy-on-write and might have to resort to
+                        * copy-on-read to protect "privileged" processes and
+                        * prevent privilege escalation.
+                        *
+                        * The root filesystem is considered "reliable" because
+                        * there's not much point in trying to protect
+                        * ourselves from such a vulnerability and the extra
+                        * cost of copy-on-read (CPU time and memory pressure)
+                        * could result in some serious regressions.
+                        */
+                       if (vp->v_mount != NULL &&
+                           ((vp->v_mount->mnt_flag & MNT_ROOTFS) ||
+                           vnode_on_reliable_media(vp))) {
+                               /*
+                                * This vnode is deemed "reliable" so mark
+                                * its VM object as "trusted".
+                                */
+                               memory_object_mark_trusted(uip->ui_control);
+                       } else {
+//                             printf("BUGGYCOW: %s:%d vp %p \"%s\" in mnt %p \"%s\" is untrusted\n", __FUNCTION__, __LINE__, vp, vp->v_name, vp->v_mount, vp->v_mount->mnt_vnodecovered->v_name);
+                       }
                }
        }
        return error;