crypto: dh - check validity of Z before export

SP800-56A rev3 section 5.7.1.1 step 2 mandates that the validity of the calculated shared secret is verified before the data is returned to the caller. This patch adds the validation check. Signed-off-by: Stephan Mueller <[email protected]> Acked-by: Neil Horman <[email protected]> Signed-off-by: Herbert Xu <[email protected]>
torvalds · Jul 31, 2020 · 90fa9ae · 90fa9ae
1 parent 4278e9d
commit 90fa9ae
Showing 1 changed file with 29 additions and 0 deletions.
diff --git a/crypto/dh.c b/crypto/dh.c
@@ -9,6 +9,7 @@
 #include <crypto/internal/kpp.h>
 #include <crypto/kpp.h>
 #include <crypto/dh.h>
+#include <linux/fips.h>
 #include <linux/mpi.h>
 
 struct dh_ctx {
@@ -179,6 +180,34 @@ static int dh_compute_value(struct kpp_request *req)
  if (ret)
  goto err_free_base;
 
+ /* SP800-56A rev3 5.7.1.1 check: Validation of shared secret */
+ if (fips_enabled && req->src) {
+ MPI pone;
+
+ /* z <= 1 */
+ if (mpi_cmp_ui(val, 1) < 1) {
+ ret = -EBADMSG;
+ goto err_free_base;
+ }
+
+ /* z == p - 1 */
+ pone = mpi_alloc(0);
+
+ if (!pone) {
+ ret = -ENOMEM;
+ goto err_free_base;
+ }
+
+ ret = mpi_sub_ui(pone, ctx->p, 1);
+ if (!ret && !mpi_cmp(pone, val))
+ ret = -EBADMSG;
+
+ mpi_free(pone);
+
+ if (ret)
+ goto err_free_base;
+ }
+
  ret = mpi_write_to_sgl(val, req->dst, req->dst_len, &sign);
  if (ret)
  goto err_free_base;