log: create log files in "fuzzing" mode if it's called outside fuzz targets

src/lxc/Makefile.am

@@ -1932,6 +1932,9 @@ init_lxc_static_CFLAGS = $(AM_CFLAGS) -DNO_LXC_CONF
 if ENABLE_SANITIZERS
 init_lxc_static_CFLAGS += -fno-sanitize=address,undefined
 endif
+if ENABLE_FUZZERS
+init_lxc_static_CFLAGS += -fno-sanitize=fuzzer-no-link
+endif
 endif
 endif
 

src/lxc/log.c

@@ -508,7 +508,10 @@ static int build_dir(const char *name)
 #ifndef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
 		ret = lxc_unpriv(mkdir(n, 0755));
 #else
-		ret = errno = EEXIST;
+		if (is_in_comm("fuzz-lxc-") > 0)
+			ret = errno = EEXIST;
+		else
+			ret = lxc_unpriv(mkdir(n, 0755));
 #endif /*!FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION */
 		*p = '/';
 		if (ret && errno != EEXIST)
@@ -521,10 +524,14 @@ static int build_dir(const char *name)
 static int log_open(const char *name)
 {
 	int newfd = -EBADF;
-#ifndef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
 	__do_close int fd = -EBADF;
 
+#ifndef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
 	fd = lxc_unpriv(open(name, O_CREAT | O_WRONLY | O_APPEND | O_CLOEXEC, 0660));
+#else
+	if (is_in_comm("fuzz-lxc-") <= 0)
+		fd = lxc_unpriv(open(name, O_CREAT | O_WRONLY | O_APPEND | O_CLOEXEC, 0660));
+#endif /* !FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION */
 	if (fd < 0)
 		return log_error_errno(-errno, errno, "Failed to open log file \"%s\"", name);
 
@@ -534,7 +541,6 @@ static int log_open(const char *name)
 	newfd = fcntl(fd, F_DUPFD_CLOEXEC, STDERR_FILENO);
 	if (newfd < 0)
 		return log_error_errno(-errno, errno, "Failed to dup log fd %d", fd);
-#endif /* !FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION */
 	return newfd;
 }
 

src/lxc/utils.h

@@ -12,6 +12,7 @@
 #include <stdarg.h>
 #include <stdbool.h>
 #include <stdio.h>
+#include <string.h>
 #include <sys/syscall.h>
 #include <sys/types.h>
 #include <sys/vfs.h>
@@ -271,4 +272,28 @@ static inline __u32 copy_struct_to_client(__u32 client_size, void *dst,
 	return size;
 }
 
+#ifdef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
+static inline int is_in_comm(const char *s)
+{
+	__do_free char *buf = NULL;
+	__do_free char *comm = NULL;
+	size_t buf_size;
+
+	buf = file_to_buf("/proc/self/comm", &buf_size);
+	if (!buf)
+		return -1;
+
+	if (buf_size == 0)
+		return -1;
+
+	comm = malloc(buf_size + 1);
+	if (!comm)
+		return -1;
+	memcpy(comm, buf, buf_size);
+	comm[buf_size] = '\0';
+
+	return strstr(comm, s) != NULL;
+}
+#endif /* FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION */
+
 #endif /* __LXC_UTILS_H */

src/tests/lxc-test-utils.c

@@ -594,6 +594,15 @@ void test_task_blocks_signal(void)
 	return;
 }
 
+void test_is_in_comm(void)
+{
+#ifdef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION
+	lxc_test_assert_abort(is_in_comm("fuzz-lxc-") == 0);
+	lxc_test_assert_abort(is_in_comm("lxc-test") == 1);
+	lxc_test_assert_abort(is_in_comm("") == 1);
+#endif /* FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION */
+}
+
 int main(int argc, char *argv[])
 {
 	test_lxc_string_replace();
@@ -606,6 +615,7 @@ int main(int argc, char *argv[])
 	test_parse_byte_size_string();
 	test_lxc_config_net_is_hwaddr();
 	test_task_blocks_signal();
+	test_is_in_comm();
 
 	exit(EXIT_SUCCESS);
 }