Add NULL pointer validation to ML-KEM EVP encapsulate/decapsulate (#3132)

Add GUARD_PTR checks for ctx and ctx->data, and explicitNULL checks for
length pointers and ciphertext buffer in pkey_kem_encapsulate and
pkey_kem_decapsulate. This matches the defensive pattern already used in
pkey_kem_encapsulate_deterministic and pkey_kem_keygen_deterministic in
the same file. Functions now return ERR_R_PASSED_NULL_PARAMETER instead
of crashing on NULL pointer arguments.

By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache 2.0 license and the ISC license.

Author: dkostic

crypto/fipsmodule/evp/p_kem.c

@@ -194,7 +194,9 @@ static int pkey_kem_encapsulate(EVP_PKEY_CTX *ctx,
                                 size_t  *ciphertext_len,
                                 uint8_t *shared_secret,
                                 size_t  *shared_secret_len) {
+  GUARD_PTR(ctx);
   KEM_PKEY_CTX *dctx = ctx->data;
+  GUARD_PTR(dctx);
   const KEM *kem = dctx->kem;
   if (kem == NULL) {
     if (ctx->pkey == NULL) {
@@ -204,6 +206,12 @@ static int pkey_kem_encapsulate(EVP_PKEY_CTX *ctx,
     kem = KEM_KEY_get0_kem(ctx->pkey->pkey.kem_key);
   }
 
+  // Check that length pointers can be written to.
+  if (ciphertext_len == NULL || shared_secret_len == NULL) {
+    OPENSSL_PUT_ERROR(EVP, ERR_R_PASSED_NULL_PARAMETER);
+    return 0;
+  }
+
   // Caller is getting parameter values.
   if (ciphertext == NULL && shared_secret == NULL) {
     *ciphertext_len = kem->ciphertext_len;
@@ -257,7 +265,9 @@ static int pkey_kem_decapsulate(EVP_PKEY_CTX *ctx,
                                 size_t  *shared_secret_len,
                                 const uint8_t *ciphertext,
                                 size_t ciphertext_len) {
+  GUARD_PTR(ctx);
   KEM_PKEY_CTX *dctx = ctx->data;
+  GUARD_PTR(dctx);
   const KEM *kem = dctx->kem;
   if (kem == NULL) {
     if (ctx->pkey == NULL) {
@@ -267,12 +277,24 @@ static int pkey_kem_decapsulate(EVP_PKEY_CTX *ctx,
     kem = KEM_KEY_get0_kem(ctx->pkey->pkey.kem_key);
   }
 
+  // Check that the length pointer can be written to.
+  if (shared_secret_len == NULL) {
+    OPENSSL_PUT_ERROR(EVP, ERR_R_PASSED_NULL_PARAMETER);
+    return 0;
+  }
+
   // Caller is getting parameter values.
   if (shared_secret == NULL) {
     *shared_secret_len = kem->shared_secret_len;
     return 1;
   }
 
+  // The ciphertext buffer must be non-NULL for actual decapsulation.
+  if (ciphertext == NULL) {
+    OPENSSL_PUT_ERROR(EVP, ERR_R_PASSED_NULL_PARAMETER);
+    return 0;
+  }
+
   // The input and output buffers need to be large enough.
   if (ciphertext_len != kem->ciphertext_len ||
       *shared_secret_len < kem->shared_secret_len) {