Fix gcc13 error: writing 1 byte into a region of size 0

gcc-13 thinks `bl` can take negative value (when returned from
EVP_CIPHER_CTX_block_size). Do simple sanity checking to workaround this.
Also, add error propagation up to EVP_DigestFinal_ex, so this sanity checking
is not in vain.

Error message:

  In function 'make_kn',
      inlined from 'CMAC_ACPKM_Final' at /builddir/build/BUILD/engine-3.0.0/gost_omac_acpkm.c:274:5,
      inlined from 'omac_acpkm_imit_final' at /builddir/build/BUILD/engine-3.0.0/gost_omac_acpkm.c:354:5:
  /builddir/build/BUILD/engine-3.0.0/gost_omac_acpkm.c:55:20: error: writing 1 byte into a region of size 0 [-Werror=stringop-overflow=]
     55 |         k1[bl - 1] ^= bl == 16 ? 0x87 : 0x1b;
        |         ~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~
  /builddir/build/BUILD/engine-3.0.0/gost_omac_acpkm.c: In function 'omac_acpkm_imit_final':
  /builddir/build/BUILD/engine-3.0.0/gost_omac_acpkm.c:260:24: note: at offset [-2147483649, -1] into destination object 'k2' of size 32
    260 |     unsigned char *k1, k2[EVP_MAX_BLOCK_LENGTH];
        |                        ^~

Fixes: https://github.com/gost-engine/engine/issues/436
Signed-off-by: Vitaly Chikunov <vt@altlinux.org>

diff --git a/gost_omac_acpkm.c b/gost_omac_acpkm.c
index 8e2c4df384343d73ce9fde474e5e83b0fb13d039..8a3c841ad269feb43b297ae38c7123c7bf630eb5 100644 (file)
--- a/gost_omac_acpkm.c
+++ b/gost_omac_acpkm.c
@@ -249,6 +249,7 @@ static int CMAC_ACPKM_Update(CMAC_ACPKM_CTX *ctx, const void *in, size_t dlen)
 
 }
 
+/* Return value is propagated to EVP_DigestFinal_ex */
 static int CMAC_ACPKM_Final(CMAC_ACPKM_CTX *ctx, unsigned char *out,
                             size_t *poutlen)
 {
@@ -257,6 +258,10 @@ static int CMAC_ACPKM_Final(CMAC_ACPKM_CTX *ctx, unsigned char *out,
     if (ctx->nlast_block == -1)
         return 0;
     bl = EVP_CIPHER_CTX_block_size(ctx->cctx);
+    if (bl != 8 && bl != 16) {
+        GOSTerr(GOST_F_OMAC_ACPKM_IMIT_FINAL, GOST_R_INVALID_MAC_PARAMS);
+        return 0;
+    }
     *poutlen = (size_t) bl;
     if (!out)
         return 1;
@@ -341,16 +346,17 @@ int omac_acpkm_imit_final(EVP_MD_CTX *ctx, unsigned char *md)
     OMAC_ACPKM_CTX *c = EVP_MD_CTX_md_data(ctx);
     unsigned char mac[MAX_GOST_OMAC_ACPKM_SIZE];
     size_t mac_size = sizeof(mac);
+    int ret;
 
     if (!c->key_set) {
         GOSTerr(GOST_F_OMAC_ACPKM_IMIT_FINAL, GOST_R_MAC_KEY_NOT_SET);
         return 0;
     }
 
-    CMAC_ACPKM_Final(c->cmac_ctx, mac, &mac_size);
+    ret = CMAC_ACPKM_Final(c->cmac_ctx, mac, &mac_size);
 
     memcpy(md, mac, c->dgst_size);
-    return 1;
+    return ret;
 }
 
 static int omac_acpkm_imit_copy(EVP_MD_CTX *to, const EVP_MD_CTX *from)