[PULL 3/6] fuzz: Expect the cmdline in a freeable GString

[Thomas Huth]

From: Alexander Bulekov <alxndr@bu.edu>

In the initial FuzzTarget, get_init_cmdline returned a char *. With this
API, we had no guarantee about where the string came from. For example,
i440fx-qtest-reboot-fuzz simply returned a pointer to a string literal,
while the QOS-based targets build the arguments out in a GString an
return the gchar *str pointer. Since we did not try to free the cmdline,
we have a leak for any targets that do not simply return string
literals. Clean up this mess by forcing fuzz-targets to return
a GString, that we can free.

Signed-off-by: Alexander Bulekov <alxndr@bu.edu>
Message-Id: <20200714174616.20709-1-alxndr@bu.edu>
Reviewed-by: Darren Kenny <darren.kenny@oracle.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
---
 tests/qtest/fuzz/fuzz.c        | 13 ++++++-------
 tests/qtest/fuzz/fuzz.h        |  6 +++---
 tests/qtest/fuzz/i440fx_fuzz.c |  4 ++--
 tests/qtest/fuzz/qos_fuzz.c    |  6 +++---
 4 files changed, 14 insertions(+), 15 deletions(-)

diff --git a/tests/qtest/fuzz/fuzz.c b/tests/qtest/fuzz/fuzz.c
index 0b66e43409..6bc17ef313 100644
--- a/tests/qtest/fuzz/fuzz.c
+++ b/tests/qtest/fuzz/fuzz.c
@@ -199,16 +199,15 @@ int LLVMFuzzerInitialize(int *argc, char ***argv, char 
***envp)
     }
 
     /* Run QEMU's softmmu main with the fuzz-target dependent arguments */
-    const char *init_cmdline = fuzz_target->get_init_cmdline(fuzz_target);
-    init_cmdline = g_strdup_printf("%s -qtest /dev/null -qtest-log %s",
-                                   init_cmdline,
-                                   getenv("QTEST_LOG") ? "/dev/fd/2"
-                                                       : "/dev/null");
-
+    GString *cmd_line = fuzz_target->get_init_cmdline(fuzz_target);
+    g_string_append_printf(cmd_line,
+                           " -qtest /dev/null -qtest-log %s",
+                           getenv("QTEST_LOG") ? "/dev/fd/2" : "/dev/null");
 
     /* Split the runcmd into an argv and argc */
     wordexp_t result;
-    wordexp(init_cmdline, &result, 0);
+    wordexp(cmd_line->str, &result, 0);
+    g_string_free(cmd_line, true);
 
     qemu_init(result.we_wordc, result.we_wordv, NULL);
 
diff --git a/tests/qtest/fuzz/fuzz.h b/tests/qtest/fuzz/fuzz.h
index 72d5710f6c..9ca3d107c5 100644
--- a/tests/qtest/fuzz/fuzz.h
+++ b/tests/qtest/fuzz/fuzz.h
@@ -50,10 +50,10 @@ typedef struct FuzzTarget {
 
 
     /*
-     * returns the arg-list that is passed to qemu/softmmu init()
-     * Cannot be NULL
+     * Returns the arguments that are passed to qemu/softmmu init(). Freed by
+     * the caller.
      */
-    const char* (*get_init_cmdline)(struct FuzzTarget *);
+    GString *(*get_init_cmdline)(struct FuzzTarget *);
 
     /*
      * will run once, prior to running qemu/softmmu init.
diff --git a/tests/qtest/fuzz/i440fx_fuzz.c b/tests/qtest/fuzz/i440fx_fuzz.c
index e2f31e56f9..bf966d478b 100644
--- a/tests/qtest/fuzz/i440fx_fuzz.c
+++ b/tests/qtest/fuzz/i440fx_fuzz.c
@@ -158,9 +158,9 @@ static void i440fx_fuzz_qos_fork(QTestState *s,
 
 static const char *i440fx_qtest_argv = TARGET_NAME " -machine accel=qtest"
                                        " -m 0 -display none";
-static const char *i440fx_argv(FuzzTarget *t)
+static GString *i440fx_argv(FuzzTarget *t)
 {
-    return i440fx_qtest_argv;
+    return g_string_new(i440fx_qtest_argv);
 }
 
 static void fork_init(void)
diff --git a/tests/qtest/fuzz/qos_fuzz.c b/tests/qtest/fuzz/qos_fuzz.c
index 0c68f5361f..d52f3ebd83 100644
--- a/tests/qtest/fuzz/qos_fuzz.c
+++ b/tests/qtest/fuzz/qos_fuzz.c
@@ -66,7 +66,7 @@ void *qos_allocate_objects(QTestState *qts, QGuestAllocator 
**p_alloc)
     return allocate_objects(qts, current_path + 1, p_alloc);
 }
 
-static const char *qos_build_main_args(void)
+static GString *qos_build_main_args(void)
 {
     char **path = fuzz_path_vec;
     QOSGraphNode *test_node;
@@ -88,7 +88,7 @@ static const char *qos_build_main_args(void)
     /* Prepend the arguments that we need */
     g_string_prepend(cmd_line,
             TARGET_NAME " -display none -machine accel=qtest -m 64 ");
-    return cmd_line->str;
+    return cmd_line;
 }
 
 /*
@@ -189,7 +189,7 @@ static void walk_path(QOSGraphNode *orig_path, int len)
     g_free(path_str);
 }
 
-static const char *qos_get_cmdline(FuzzTarget *t)
+static GString *qos_get_cmdline(FuzzTarget *t)
 {
     /*
      * Set a global variable that we use to identify the qos_path for our
-- 
2.18.1