util: add base64 decoding function

The standard glib provided g_base64_decode doesn't provide any
kind of sensible error checking on its input. Add a QEMU custom
wrapper qbase64_decode which can be used with untrustworthy
input that can contain invalid base64 characters, embedded
NUL characters, or not be NUL terminated at all.

Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>

include/qemu/base64.h

+/*
+ * QEMU base64 helpers
+ *
+ * Copyright (c) 2015 Red Hat, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#ifndef QEMU_BASE64_H__
+#define QEMU_BASE64_H__
+
+#include "qemu-common.h"
+
+
+/**
+ * qbase64_decode:
+ * @input: the (possibly) base64 encoded text
+ * @in_len: length of @input or -1 if NUL terminated
+ * @out_len: filled with length of decoded data
+ * @errp: pointer to a NULL-initialized error object
+ *
+ * Attempt to decode the (possibly) base64 encoded
+ * text provided in @input. If the @input text may
+ * contain embedded NUL characters, or may not be
+ * NUL terminated, then @in_len must be set to the
+ * known size of the @input buffer.
+ *
+ * Note that embedded NULs, or lack of a NUL terminator
+ * are considered invalid base64 data and errors
+ * will be reported to this effect.
+ *
+ * If decoding is successful, the decoded data will
+ * be returned and @out_len set to indicate the
+ * number of bytes in the decoded data. The caller
+ * must use g_free() to free the returned data when
+ * it is no longer required.
+ *
+ * Returns: the decoded data or NULL
+ */
+uint8_t *qbase64_decode(const char *input,
+                        size_t in_len,
+                        size_t *out_len,
+                        Error **errp);
+
+
+#endif /* QEMU_BUFFER_H__ */

tests/.gitignore

@@ -8,6 +8,7 @@ check-qom-interface
 check-qom-proplist
 rcutorture
 test-aio
+test-base64
 test-bitops
 test-blockjob-txn
 test-coroutine

tests/Makefile

@@ -90,6 +90,7 @@ check-unit-y += tests/test-io-channel-file$(EXESUF)
 check-unit-$(CONFIG_GNUTLS) += tests/test-io-channel-tls$(EXESUF)
 check-unit-y += tests/test-io-channel-command$(EXESUF)
 check-unit-y += tests/test-io-channel-buffer$(EXESUF)
+check-unit-y += tests/test-base64$(EXESUF)
 
 check-block-$(CONFIG_POSIX) += tests/qemu-iotests-quick.sh
 
@@ -423,6 +424,8 @@ tests/test-vmstate$(EXESUF): tests/test-vmstate.o \
 	$(test-qom-obj-y)
 tests/test-timed-average$(EXESUF): tests/test-timed-average.o qemu-timer.o \
 	$(test-util-obj-y)
+tests/test-base64$(EXESUF): tests/test-base64.o \
+	libqemuutil.a libqemustub.a
 
 tests/test-qapi-types.c tests/test-qapi-types.h :\
 $(SRC_PATH)/tests/qapi-schema/qapi-schema-test.json $(SRC_PATH)/scripts/qapi-types.py $(qapi-py)

tests/test-base64.c

+/*
+ * QEMU base64 helper test
+ *
+ * Copyright (c) 2015 Red Hat, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include <glib.h>
+
+#include "qemu/base64.h"
+
+
+static void test_base64_good(void)
+{
+    const char input[] =
+        "QmVjYXVzZSB3ZSBmb2N1c2VkIG9uIHRoZSBzbmFrZSwgd2UgbW\n"
+        "lzc2VkIHRoZSBzY29ycGlvbi4=";
+    const char expect[] = "Because we focused on the snake, "
+        "we missed the scorpion.";
+
+    size_t len;
+    uint8_t *actual = qbase64_decode(input,
+                                     -1,
+                                     &len,
+                                     &error_abort);
+
+    g_assert(actual != NULL);
+    g_assert_cmpint(len, ==, strlen(expect));
+    g_assert_cmpstr((char *)actual, ==, expect);
+    g_free(actual);
+}
+
+
+static void test_base64_bad(const char *input,
+                            size_t input_len)
+{
+    size_t len;
+    Error *err = NULL;
+    uint8_t *actual = qbase64_decode(input,
+                                     input_len,
+                                     &len,
+                                     &err);
+
+    g_assert(err != NULL);
+    g_assert(actual == NULL);
+    g_assert_cmpint(len, ==, 0);
+    error_free(err);
+}
+
+
+static void test_base64_embedded_nul(void)
+{
+    /* We put a NUL character in the middle of the base64
+     * text which is invalid data, given the expected length */
+    const char input[] =
+        "QmVjYXVzZSB3ZSBmb2N1c2VkIG9uIHRoZSBzbmFrZSwgd2UgbW\0"
+        "lzc2VkIHRoZSBzY29ycGlvbi4=";
+
+    test_base64_bad(input, G_N_ELEMENTS(input) - 1);
+}
+
+
+static void test_base64_not_nul_terminated(void)
+{
+    const char input[] =
+        "QmVjYXVzZSB3ZSBmb2N1c2VkIG9uIHRoZSBzbmFrZSwgd2UgbW\n"
+        "lzc2VkIHRoZSBzY29ycGlvbi4=";
+
+    /* Using '-2' to make us drop the trailing NUL, thus
+     * creating an invalid base64 sequence for decoding */
+    test_base64_bad(input, G_N_ELEMENTS(input) - 2);
+}
+
+
+static void test_base64_invalid_chars(void)
+{
+    /* We put a single quote character in the middle
+     * of the base64 text which is invalid data */
+    const char input[] =
+        "QmVjYXVzZSB3ZSBmb2N1c2VkIG9uIHRoZSBzbmFrZSwgd2UgbW'"
+        "lzc2VkIHRoZSBzY29ycGlvbi4=";
+
+    test_base64_bad(input, strlen(input));
+}
+
+
+int main(int argc, char **argv)
+{
+    g_test_init(&argc, &argv, NULL);
+    g_test_add_func("/util/base64/good", test_base64_good);
+    g_test_add_func("/util/base64/embedded-nul", test_base64_embedded_nul);
+    g_test_add_func("/util/base64/not-nul-terminated",
+                    test_base64_not_nul_terminated);
+    g_test_add_func("/util/base64/invalid-chars", test_base64_invalid_chars);
+    return g_test_run();
+}

util/Makefile.objs

@@ -30,3 +30,4 @@ util-obj-y += qemu-coroutine-sleep.o
 util-obj-y += coroutine-$(CONFIG_COROUTINE_BACKEND).o
 util-obj-y += buffer.o
 util-obj-y += timed-average.o
+util-obj-y += base64.o

util/base64.c

+/*
+ * QEMU base64 helpers
+ *
+ * Copyright (c) 2015 Red Hat, Inc.
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include <config-host.h>
+
+#include "qemu/base64.h"
+
+static const char *base64_valid_chars =
+    "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/=\n";
+
+uint8_t *qbase64_decode(const char *input,
+                        size_t in_len,
+                        size_t *out_len,
+                        Error **errp)
+{
+    *out_len = 0;
+
+    if (in_len != -1) {
+        /* Lack of NUL terminator is an error */
+        if (input[in_len] != '\0') {
+            error_setg(errp, "Base64 data is not NUL terminated");
+            return NULL;
+        }
+        /* Check there's no NULs embedded since we expect
+         * this to be valid base64 data */
+        if (memchr(input, '\0', in_len) != NULL) {
+            error_setg(errp, "Base64 data contains embedded NUL characters");
+            return NULL;
+        }
+
+        /* Now we know its a valid nul terminated string
+         * strspn is safe to use... */
+    } else {
+        in_len = strlen(input);
+    }
+
+    if (strspn(input, base64_valid_chars) != in_len) {
+        error_setg(errp, "Base64 data contains invalid characters");
+        return NULL;
+    }
+
+    return g_base64_decode(input, out_len);
+}