comedi: drivers: ni_routes: Use strcmp() instead of memcmp()

The family and device comparisons were using memcmp(), but this could
lead to Out-of-bounds reads when the length was larger than the
buffers being compared. Since these appear to always be NUL-terminated
strings, just use strcmp() instead.

This was found with Clang under LTO:

[ 92.405851][    T1] kernel BUG at lib/string_helpers.c:980!
...
[ 92.409141][ T1] RIP: 0010:fortify_panic (fbdev.c:?)
...
[ 92.410056][ T1] ni_assign_device_routes (fbdev.c:?)
[ 92.410056][ T1] ? unittest_enter (fbdev.c:?)
[ 92.410056][ T1] ni_routes_unittest (ni_routes_test.c:?)
[ 92.410056][ T1] ? unittest_enter (fbdev.c:?)
[ 92.410056][ T1] __initstub__kmod_ni_routes_test__505_604_ni_routes_unittest6 (fbdev.c:?)
[ 92.410056][ T1] do_one_initcall (fbdev.c:?)

Link: https://lore.kernel.org/lkml/20220210072821.GD4074@xsang-OptiPlex-9020
Fixes: 4bb90c87abbe ("staging: comedi: add interface to ni routing table information")
Cc: Ian Abbott <abbotti@mev.co.uk>
Cc: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: Spencer E. Olson <olsonse@umich.edu>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Lee Jones <lee.jones@linaro.org>
Reported-by: kernel test robot <oliver.sang@intel.com>
Reviewed-by: Ian Abbott <abbotti@mev.co.uk>
Signed-off-by: Kees Cook <keescook@chromium.org>
Link: https://lore.kernel.org/r/20220215171017.1247291-1-keescook@chromium.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/comedi/drivers/ni_routes.c b/drivers/comedi/drivers/ni_routes.c
index f24eeb464eba68391d67e9edb81213e1173d8569..295a3a9ee0c95f20d37b2819993896e54affc940 100644 (file)
--- a/drivers/comedi/drivers/ni_routes.c
+++ b/drivers/comedi/drivers/ni_routes.c
@@ -56,8 +56,7 @@ static const u8 *ni_find_route_values(const char *device_family)
        int i;
 
        for (i = 0; ni_all_route_values[i]; ++i) {
-               if (memcmp(ni_all_route_values[i]->family, device_family,
-                          strnlen(device_family, 30)) == 0) {
+               if (!strcmp(ni_all_route_values[i]->family, device_family)) {
                        rv = &ni_all_route_values[i]->register_values[0][0];
                        break;
                }
@@ -75,8 +74,7 @@ ni_find_valid_routes(const char *board_name)
        int i;
 
        for (i = 0; ni_device_routes_list[i]; ++i) {
-               if (memcmp(ni_device_routes_list[i]->device, board_name,
-                          strnlen(board_name, 30)) == 0) {
+               if (!strcmp(ni_device_routes_list[i]->device, board_name)) {
                        dr = ni_device_routes_list[i];
                        break;
                }