Fix error handling on gf_ivnert_matrix in isa-l backend

Current isa-l has possibility to return corrupted decoded data or
corrupted reconstructed data on decode/reconstruct without error code.

That is from the specification of isa-l rs vandermond matrix discussed
at [1]. With many # of parities cases, we may hit the case above due to
failing to get the inverse matrix from the encode matrix.

The isa-l maintener gbtucker suggests a good way to detect the failing
inverse matrix, that we should handle the return value gf_invert_matrix.
If gf_invert_matrix returns not 0, we should stop to decode/reconstruct
and return failure return code to the caller immediately. Otherwise, the
caller regards the garbage data/fragment as correct one.

And this patch adds the specific test case we can hit the issue (it
happens not so general).

1: https://github.com/01org/isa-l/issues/10

Related-Change: I6eb150d9d0c3febf233570fa7729f9f72df2e9be
Change-Id: Icee788a0931fe692fe0de31fabc4ba450e338a87

src/backends/isa-l/isa_l_rs_vand.c

@@ -261,7 +261,10 @@ static int isa_l_rs_vand_decode(void *desc, char **data, char **parity,
         goto out;
     }
 
-    isa_l_desc->gf_invert_matrix(decode_matrix, decode_inverse, k);
+    int im_ret = isa_l_desc->gf_invert_matrix(decode_matrix, decode_inverse, k);
+    if (im_ret < 0) {
+        goto out;
+    }
 
     // Generate g_tbls from computed decode matrix (k x k) matrix
     g_tbls = malloc(sizeof(unsigned char) * (k * m * 32));
@@ -365,7 +368,10 @@ static int isa_l_rs_vand_reconstruct(void *desc, char **data, char **parity,
         goto out;
     }
 
-    isa_l_desc->gf_invert_matrix(decode_matrix, decode_inverse, k);
+    int im_ret = isa_l_desc->gf_invert_matrix(decode_matrix, decode_inverse, k);
+    if (im_ret < 0) {
+        goto out;
+    }
 
     /**
      * Get the row needed to reconstruct

test/liberasurecode_test.c

@@ -1346,6 +1346,102 @@ static void test_decode_with_missing_multi_data_parity(
     }
 }
 
+static void test_decode_reconstruct_specific_error_case(
+    const ec_backend_id_t be_id, struct ec_args *args)
+{
+    struct ec_args specific_1010_args = {
+        .k = 10,
+        .m = 10,
+    };
+
+    int rc = 0;
+    int desc = -1;
+    int orig_data_size = 1024 * 1024;
+    char *orig_data = create_buffer(orig_data_size, 'x');
+    char **encoded_data = NULL, **encoded_parity = NULL;
+    uint64_t encoded_fragment_len = 0;
+    int num_avail_frags = -1;
+    char **avail_frags = NULL;
+    char *decoded_data = NULL;
+    char *out_frag = NULL;
+    uint64_t decoded_data_len = 0;
+
+    int *skips = create_skips_array(&specific_1010_args,-1);
+    assert(skips != NULL);
+    // available frags for a bad pattern: [0, 1, 2, 3, 4, 6, 7, 10, 12, 15]
+    skips[5] = skips[8] = skips[9] = skips[11] = skips[13] = skips[14] =
+        skips[16] = skips[17] = skips[18] = skips[19] = 1;
+
+    desc = liberasurecode_instance_create(
+        EC_BACKEND_ISA_L_RS_VAND, &specific_1010_args);
+    if (-EBACKENDNOTAVAIL == desc) {
+        fprintf (stderr, "Backend library not available!\n");
+        return;
+    }
+    assert(desc > 0);
+
+    rc = liberasurecode_encode(desc, orig_data, orig_data_size,
+            &encoded_data, &encoded_parity, &encoded_fragment_len);
+    assert(rc == 0);
+
+    num_avail_frags = create_frags_array(&avail_frags, encoded_data,
+                                         encoded_parity, &specific_1010_args,
+                                         skips);
+    assert(num_avail_frags > 0);
+
+    rc = liberasurecode_decode(desc, avail_frags, num_avail_frags,
+                               encoded_fragment_len, 1,
+                               &decoded_data, &decoded_data_len);
+    assert(rc == -1);
+    free(avail_frags);
+
+    // 5 is a hole in available frags
+    num_avail_frags = create_frags_array(&avail_frags, encoded_data,
+                                         encoded_parity, &specific_1010_args,
+                                         skips);
+    out_frag = malloc(sizeof(char) * encoded_fragment_len);
+    rc = liberasurecode_reconstruct_fragment(
+        desc, avail_frags, 10, encoded_fragment_len, 5, out_frag);
+    assert(rc == -1);
+
+    free(out_frag);
+    free(avail_frags);
+
+    // sanity; [0, 1, 2, 3, 4, 6, 7, 10, 12, 14] is ok
+    skips[15] = 1; skips[14] = 0;
+    num_avail_frags = create_frags_array(&avail_frags, encoded_data,
+                                         encoded_parity, &specific_1010_args,
+                                         skips);
+    assert(num_avail_frags > 0);
+    rc = liberasurecode_decode(desc, avail_frags, num_avail_frags,
+                               encoded_fragment_len, 1,
+                               &decoded_data, &decoded_data_len);
+    assert(rc == 0);
+    // 5 is a hole in available frags
+    out_frag = malloc(sizeof(char) * encoded_fragment_len);
+    rc = liberasurecode_reconstruct_fragment(
+        desc, avail_frags, 10, encoded_fragment_len, 5, out_frag);
+
+    assert(rc == 0);
+
+    free(out_frag);
+
+    // cleanup all
+    rc = liberasurecode_encode_cleanup(desc, encoded_data, encoded_parity);
+    assert(rc == 0);
+
+    rc = liberasurecode_decode_cleanup(desc, decoded_data);
+    assert(rc == 0);
+
+    if (desc) {
+        assert(0 == liberasurecode_instance_destroy(desc));
+    }
+
+    free(orig_data);
+    free(avail_frags);
+    free(skips);
+}
+
 static void test_simple_encode_decode(const ec_backend_id_t be_id,
                                      struct ec_args *args)
 {
@@ -1875,6 +1971,10 @@ struct testcase testcases[] = {
         test_verify_stripe_metadata_frag_idx_invalid,
         EC_BACKEND_ISA_L_RS_VAND, CHKSUM_CRC32,
         .skip = false},
+    {"test_isa_l_decode_reconstruct_specific_error_case",
+        test_decode_reconstruct_specific_error_case,
+        EC_BACKENDS_MAX, 0, // note this test is using ISA-L in hard coded
+        .skip = false},
     // shss tests
     {"create_and_destroy_backend",
         test_create_and_destroy_backend,