New macro TEST_ASSERT_ERRNO

Show errno if a test assertion fails.

Signed-off-by: Gilles Peskine <[email protected]>

tests/include/test/helpers.h

@@ -240,6 +240,19 @@ void mbedtls_test_platform_teardown(void);
  */
 void mbedtls_test_fail(const char *test, int line_no, const char *filename);
 
+/**
+ * \brief           Record the current test case as a failure
+ *                  and show the value of errno.
+ *
+ *                  This function is usually called via #TEST_ASSERT_ERRNO.
+ *
+ * \param test      Description of the failure or assertion that failed. This
+ *                  MUST be a string literal.
+ * \param line_no   Line number where the failure originated.
+ * \param filename  Filename where the failure originated.
+ */
+void mbedtls_test_fail_errno(const char *test, int line_no, const char *filename);
+
 /**
  * \brief           Record the current test case as skipped.
  *

tests/include/test/macros.h

@@ -54,6 +54,21 @@
         }                                                    \
     } while (0)
 
+/** \brief Evaluate an integer expression. If the value is 0 (i.e. false),
+ *         mark the test case as failed and display errno.
+ *
+ * This is intended for functions that follow the Unix API convention of
+ * returning a particular value (often -1) and setting errno on failure,
+ * e.g. `TEST_ASSERT_ERRNO(open(...) != -1)`.
+ */
+#define TEST_ASSERT_ERRNO(expr)                                         \
+    do {                                                                \
+        if (!(expr)) {                                                  \
+            mbedtls_test_fail_errno(#expr, __LINE__, __FILE__);         \
+            goto exit;                                                  \
+        }                                                               \
+    } while (0)
+
 /** This macro asserts fails the test with given output message.
  *
  * \param   MESSAGE The message to be outputed on assertion

tests/src/helpers.c

@@ -6,6 +6,7 @@
 #include <test/constant_flow.h>
 #include <test/helpers.h>
 #include <test/macros.h>
+#include <errno.h>
 #include <string.h>
 
 #if defined(MBEDTLS_PSA_INJECT_ENTROPY)
@@ -571,6 +572,31 @@ int mbedtls_test_le_s(const char *test, int line_no, const char *filename,
     return 0;
 }
 
+void mbedtls_test_fail_errno(const char *test,
+                             int line_no, const char *filename)
+{
+#ifdef MBEDTLS_THREADING_C
+    mbedtls_mutex_lock(&mbedtls_test_info_mutex);
+#endif /* MBEDTLS_THREADING_C */
+
+    /* Don't use accessor, we already hold mutex. */
+    if (mbedtls_test_info.result != MBEDTLS_TEST_RESULT_FAILED) {
+        /* If we've already recorded the test as having failed then don't
+         * overwrite any previous information about the failure. */
+
+        char buf[MBEDTLS_TEST_LINE_LENGTH];
+        mbedtls_test_fail_internal(test, line_no, filename);
+        (void) mbedtls_snprintf(buf, sizeof(buf),
+                                "errno = %d (%s)",
+                                errno, strerror(errno));
+        mbedtls_test_set_line1_internal(buf);
+    }
+
+#ifdef MBEDTLS_THREADING_C
+    mbedtls_mutex_unlock(&mbedtls_test_info_mutex);
+#endif /* MBEDTLS_THREADING_C */
+}
+
 int mbedtls_test_unhexify(unsigned char *obuf,
                           size_t obufmax,
                           const char *ibuf,