Eradicate VLAs from the codebase

They are already banned in e.g. the Linux kernel, and are considered a
security risk by many projects.

Also fix a -Wformat-nonliteral warning from clang.

daemon/Makefile

@@ -5,7 +5,7 @@ override QUBES_CFLAGS:=-I../libqrexec -g -O2 -Wall -Wextra -Werror -fPIC \
    -D_FORTIFY_SOURCE=2 -fstack-protector-strong -std=gnu11 -D_POSIX_C_SOURCE=200809L \
    -D_GNU_SOURCE $(CFLAGS) \
    -Wstrict-prototypes -Wold-style-definition -Wmissing-declarations \
-   -fvisibility=hidden -fno-strict-aliasing
+   -fvisibility=hidden -fno-strict-aliasing -Wvla
 override LDFLAGS += -pie -Wl,-z,relro,-z,now -L../libqrexec
 override LDLIBS += $(shell pkg-config --libs $(VCHAN_PKG)) -lqrexec-utils
 

daemon/qrexec-daemon.c

@@ -140,23 +140,19 @@ static int remote_domain_id;
 
 static void unlink_qrexec_socket(void)
 {
-    char socket_address[40];
-    char link_to_socket_name[strlen(remote_domain_name) + sizeof(socket_address)];
+    char *socket_address;
+    char *link_to_socket_name;
 
-    int v = snprintf(socket_address, sizeof(socket_address),
-                     "qrexec.%d", remote_domain_id);
-    if (v < (int)sizeof("qrexec.1") - 1 || v >= (int)sizeof(socket_address))
-        abort();
-    v = snprintf(link_to_socket_name, sizeof(link_to_socket_name),
-                 "qrexec.%s", remote_domain_name);
-    if (v < (int)sizeof("qrexec.") - 1 || v >= (int)sizeof(link_to_socket_name))
-        abort();
-    v = unlink(socket_address);
-    if (v != 0 && !(v == -1 && errno == ENOENT))
+    if (asprintf(&socket_address, "%s/qrexec.%d", socket_dir, remote_domain_id) < 0)
+        err(1, "asprintf");
+    if (unlink(socket_address) != 0 && errno != ENOENT)
         err(1, "unlink(%s)", socket_address);
-    v = unlink(link_to_socket_name);
-    if (v != 0 && !(v == -1 && errno == ENOENT))
+    free(socket_address);
+    if (asprintf(&link_to_socket_name, "%s/qrexec.%s", socket_dir, remote_domain_name) < 0)
+        err(1, "asprintf");
+    if (unlink(link_to_socket_name) != 0 && errno != ENOENT)
         err(1, "unlink(%s)", link_to_socket_name);
+    free(link_to_socket_name);
 }
 
 static void handle_vchan_error(const char *op)
@@ -169,18 +165,14 @@ static void handle_vchan_error(const char *op)
 static int create_qrexec_socket(int domid, const char *domname)
 {
     char socket_address[40];
-    char link_to_socket_name[strlen(domname) + sizeof(socket_address)];
-    int res;
-
-    if ((unsigned)snprintf(socket_address, sizeof(socket_address),
-                           "qrexec.%d", domid) >= sizeof(socket_address))
-        errx(1, "socket name too long");
-    if ((unsigned)snprintf(link_to_socket_name, sizeof link_to_socket_name,
-                           "qrexec.%s", domname) >= sizeof link_to_socket_name)
-        errx(1, "socket link name too long");
-    res = unlink(link_to_socket_name);
-    if (res != 0 && !(res == -1 && errno == ENOENT))
-        err(1, "unlink(%s)", link_to_socket_name);
+    char *link_to_socket_name;
+
+    snprintf(socket_address, sizeof(socket_address),
+             "%s/qrexec.%d", socket_dir, domid);
+    if (asprintf(&link_to_socket_name,
+                 "%s/qrexec.%s", socket_dir, domname) < 0)
+        err(1, "asprintf");
+    unlink(link_to_socket_name);
 
     /* When running as root, make the socket accessible; perms on /var/run/qubes still apply */
     umask(0);
@@ -189,6 +181,7 @@ static int create_qrexec_socket(int domid, const char *domname)
     }
     int fd = get_server_socket(socket_address);
     umask(0077);
+    free(link_to_socket_name);
     return fd;
 }
 

libqrexec/Makefile

@@ -5,7 +5,8 @@ override QUBES_CFLAGS := -I. -I../libqrexec -g -O2 -Wall -Wextra -Werror \
    -D_FORTIFY_SOURCE=2 -fstack-protector-strong -fPIC -std=gnu11 -D_POSIX_C_SOURCE=200809L \
    -D_GNU_SOURCE $(CFLAGS) \
    -Wstrict-prototypes -Wold-style-definition -Wmissing-declarations \
-   -fno-delete-null-pointer-checks -fvisibility=hidden
+   -fno-delete-null-pointer-checks -fvisibility=hidden \
+   -Wvla -Wformat=2
 
 override LDFLAGS += -pie -Wl,-z,relro,-z,now -shared
 

libqrexec/log.c

@@ -32,7 +32,7 @@
 static const char *qrexec_program_name = "qrexec";
 
 static void log_time(void) {
-    const size_t buf_len = 32;
+#define buf_len 32
     char buf[buf_len];
     struct tm tm_buf;
     struct tm *tm;
@@ -46,12 +46,14 @@ static void log_time(void) {
 
     strftime(buf, buf_len, "%Y-%m-%d %H:%M:%S", tm);
     fprintf(stderr, "%s.%03d ", buf, (int)(tv.tv_usec / 1000));
+#undef buf_len
 }
 
-static void qrexec_logv(__attribute__((unused)) int level, int errnoval,
-                        const char *file, int line,
-                        const char *func, const char *fmt, va_list ap) {
-    const size_t buf_len = 64;
+static void __attribute__((format(printf, 6, 0)))
+qrexec_logv(__attribute__((unused)) int level, int errnoval,
+            const char *file, int line,
+            const char *func, const char *fmt, va_list ap) {
+#define buf_len 64
     char buf[buf_len];
     char *err;
     int _errno = errno;
@@ -65,6 +67,7 @@ static void qrexec_logv(__attribute__((unused)) int level, int errnoval,
     fprintf(stderr, "\n");
     fflush(stderr);
     errno = _errno;
+#undef buf_len
 }
 
 void qrexec_log(int level, int errnoval, const char *file, int line,