misc: mic/scif: fix wrap around tests

BugLink: http://bugs.launchpad.net/bugs/1578798

commit 7b64dbf8 upstream.

Signed integer overflow is undefined.  Also I added a check for
"(offset < 0)" in scif_unregister() because that makes it match the
other conditions and because I didn't want to subtract a negative.

Fixes: ba612aa8 ('misc: mic: SCIF memory registration and unregistration')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>

drivers/misc/mic/scif/scif_rma.c

@@ -1511,7 +1511,7 @@ off_t scif_register_pinned_pages(scif_epd_t epd,
 	if ((map_flags & SCIF_MAP_FIXED) &&
 	    ((ALIGN(offset, PAGE_SIZE) != offset) ||
 	    (offset < 0) ||
-	    (offset + (off_t)len < offset)))
+	    (len > LONG_MAX - offset)))
 		return -EINVAL;
 
 	might_sleep();
@@ -1614,7 +1614,7 @@ off_t scif_register(scif_epd_t epd, void *addr, size_t len, off_t offset,
 	if ((map_flags & SCIF_MAP_FIXED) &&
 	    ((ALIGN(offset, PAGE_SIZE) != offset) ||
 	    (offset < 0) ||
-	    (offset + (off_t)len < offset)))
+	    (len > LONG_MAX - offset)))
 		return -EINVAL;
 
 	/* Unsupported protection requested */
@@ -1732,7 +1732,8 @@ scif_unregister(scif_epd_t epd, off_t offset, size_t len)
 
 	/* Offset is not page aligned or offset+len wraps around */
 	if ((ALIGN(offset, PAGE_SIZE) != offset) ||
-	    (offset + (off_t)len < offset))
+	    (offset < 0) ||
+	    (len > LONG_MAX - offset))
 		return -EINVAL;
 
 	err = scif_verify_epd(ep);