[OpenWrt-Devel] [PATCH uci 2/2] build: Add -Wclobbered to detect problems with longjmp

[Hauke Mehrtens]

When we jump back to a save point in UCI_THROW() with longjmp all the
registers will be reset to the old values when we called UCI_TRAP_SAVE()
last time, but the memory is not restored. This will revert all the
variables which are stored in registers, but not the variables stored on
the stack.

Mark all the variables which the compiler could put into a register as
volatile to store them safely on the stack and make sure they have the
defined current values also after longjmp was called.

This also activates a compiler warning which should warn us in such
cases.
This could fix some potential problem in error paths like the one
reported in CVE-2019-15513.

Signed-off-by: Hauke Mehrtens <hauke at hauke-m.de>
---
 CMakeLists.txt |  2 +-
 delta.c        | 20 ++++++++++----------
 file.c         | 11 ++++++-----
 list.c         |  4 ++--
 4 files changed, 19 insertions(+), 18 deletions(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 170eb0b..578c021 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -3,7 +3,7 @@ cmake_minimum_required(VERSION 2.6)
 PROJECT(uci C)
 
 SET(CMAKE_SHARED_LIBRARY_LINK_C_FLAGS "")
-ADD_DEFINITIONS(-Os -Wall -Werror --std=gnu99 -g3 -I. -DUCI_PREFIX="${CMAKE_INSTALL_PREFIX}")
+ADD_DEFINITIONS(-Os -Wall -Werror -Wclobbered --std=gnu99 -g3 -I. -DUCI_PREFIX="${CMAKE_INSTALL_PREFIX}")
 
 OPTION(UCI_DEBUG "debugging support" OFF)
 OPTION(UCI_DEBUG_TYPECAST "typecast debugging support" OFF)
diff --git a/delta.c b/delta.c
index 386167d..52ebe3b 100644
--- a/delta.c
+++ b/delta.c
@@ -100,7 +100,7 @@ int uci_set_savedir(struct uci_context *ctx, const char *dir)
 {
 	char *sdir;
 	struct uci_element *e, *tmp;
-	bool exists = false;
+	volatile bool exists = false;
 
 	UCI_HANDLE_ERR(ctx);
 	UCI_ASSERT(ctx, dir != NULL);
@@ -259,7 +259,7 @@ error:
 static int uci_parse_delta(struct uci_context *ctx, FILE *stream, struct uci_package *p)
 {
 	struct uci_parse_context *pctx;
-	int changes = 0;
+	volatile int changes = 0;
 
 	/* make sure no memory from previous parse attempts is leaked */
 	uci_cleanup(ctx);
@@ -294,8 +294,8 @@ error:
 /* returns the number of changes that were successfully parsed */
 static int uci_load_delta_file(struct uci_context *ctx, struct uci_package *p, char *filename, FILE **f, bool flush)
 {
-	FILE *stream = NULL;
-	int changes = 0;
+	FILE *volatile stream = NULL;
+	volatile int changes = 0;
 
 	UCI_TRAP_SAVE(ctx, done);
 	stream = uci_open_stream(ctx, filename, NULL, SEEK_SET, flush, false);
@@ -317,8 +317,8 @@ __private int uci_load_delta(struct uci_context *ctx, struct uci_package *p, boo
 {
 	struct uci_element *e;
 	char *filename = NULL;
-	FILE *f = NULL;
-	int changes = 0;
+	FILE *volatile f = NULL;
+	volatile int changes = 0;
 
 	if (!p->has_delta)
 		return 0;
@@ -419,9 +419,9 @@ done:
 
 int uci_revert(struct uci_context *ctx, struct uci_ptr *ptr)
 {
-	char *package = NULL;
-	char *section = NULL;
-	char *option = NULL;
+	char *volatile package = NULL;
+	char *volatile section = NULL;
+	char *volatile option = NULL;
 
 	UCI_HANDLE_ERR(ctx);
 	uci_expand_ptr(ctx, ptr, false);
@@ -463,7 +463,7 @@ error:
 
 int uci_save(struct uci_context *ctx, struct uci_package *p)
 {
-	FILE *f = NULL;
+	FILE *volatile f = NULL;
 	char *filename = NULL;
 	struct uci_element *e, *tmp;
 	struct stat statbuf;
diff --git a/file.c b/file.c
index 7333e48..321b66b 100644
--- a/file.c
+++ b/file.c
@@ -721,10 +721,10 @@ static void uci_file_commit(struct uci_context *ctx, struct uci_package **packag
 {
 	struct uci_package *p = *package;
 	FILE *f1, *f2 = NULL;
-	char *name = NULL;
-	char *path = NULL;
+	char *volatile name = NULL;
+	char *volatile path = NULL;
 	char *filename = NULL;
-	bool do_rename = false;
+	volatile bool do_rename = false;
 	int fd;
 
 	if (!p->path) {
@@ -881,12 +881,13 @@ static char **uci_list_config_files(struct uci_context *ctx)
 	return configs;
 }
 
-static struct uci_package *uci_file_load(struct uci_context *ctx, const char *name)
+static struct uci_package *uci_file_load(struct uci_context *ctx,
+					 const char *volatile name)
 {
 	struct uci_package *package = NULL;
 	char *filename;
 	bool confdir;
-	FILE *file = NULL;
+	FILE *volatile file = NULL;
 
 	switch (name[0]) {
 	case '.':
diff --git a/list.c b/list.c
index 78efbaf..41a8702 100644
--- a/list.c
+++ b/list.c
@@ -623,8 +623,8 @@ int uci_add_list(struct uci_context *ctx, struct uci_ptr *ptr)
 {
 	/* NB: UCI_INTERNAL use means without delta tracking */
 	bool internal = ctx && ctx->internal;
-	struct uci_option *prev = NULL;
-	const char *value2 = NULL;
+	struct uci_option *volatile prev = NULL;
+	const char *volatile value2 = NULL;
 
 	UCI_HANDLE_ERR(ctx);
 
-- 
2.20.1


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