use st_add and st_mult for allocation size computation

If our size computation overflows size_t, we may allocate a
much smaller buffer than we expected and overflow it. It's
probably impossible to trigger an overflow in most of these
sites in practice, but it is easy enough convert their
additions and multiplications into overflow-checking
variants. This may be fixing real bugs, and it makes
auditing the code easier.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

4 files changed, 6 insertions, 6 deletions

diff --git a/compat/mingw.c b/compat/mingw.c
index d8a5345a3..ae16d089a 100644
--- a/compat/mingw.c
+++ b/compat/mingw.c
@@ -769,7 +769,7 @@ static const char *quote_arg(const char *arg)
 		return arg;
 
 	/* insert \ where necessary */
-	d = q = xmalloc(len+n+3);
+	d = q = xmalloc(st_add3(len, n, 3));
 	*d++ = '"';
 	while (*arg) {
 		if (*arg == '"')
@@ -1028,7 +1028,7 @@ static pid_t mingw_spawnve_fd(const char *cmd, const char **argv, char **deltaen
 			free(quoted);
 	}
 
-	wargs = xmalloc((2 * args.len + 1) * sizeof(wchar_t));
+	wargs = xmalloc_array(st_add(st_mult(2, args.len), 1), sizeof(wchar_t));
 	xutftowcs(wargs, args.buf, 2 * args.len + 1);
 	strbuf_release(&args);
 
diff --git a/compat/qsort.c b/compat/qsort.c
index 9574d537b..7d071afb7 100644
--- a/compat/qsort.c
+++ b/compat/qsort.c
@@ -47,7 +47,7 @@ static void msort_with_tmp(void *b, size_t n, size_t s,
 void git_qsort(void *b, size_t n, size_t s,
 	       int (*cmp)(const void *, const void *))
 {
-	const size_t size = n * s;
+	const size_t size = st_mult(n, s);
 	char buf[1024];
 
 	if (size < sizeof(buf)) {
diff --git a/compat/setenv.c b/compat/setenv.c
index fc1439a64..7849f258d 100644
--- a/compat/setenv.c
+++ b/compat/setenv.c
@@ -18,7 +18,7 @@ int gitsetenv(const char *name, const char *value, int replace)
 
 	namelen = strlen(name);
 	valuelen = strlen(value);
-	envstr = malloc((namelen + valuelen + 2));
+	envstr = malloc(st_add3(namelen, valuelen, 2));
 	if (!envstr) {
 		errno = ENOMEM;
 		return -1;
diff --git a/compat/win32/syslog.c b/compat/win32/syslog.c
index d015e436d..b905aea31 100644
--- a/compat/win32/syslog.c
+++ b/compat/win32/syslog.c
@@ -32,7 +32,7 @@ void syslog(int priority, const char *fmt, ...)
 		return;
 	}
 
-	str = malloc(str_len + 1);
+	str = malloc(st_add(str_len, 1));
 	if (!str) {
 		warning("malloc failed: '%s'", strerror(errno));
 		return;
@@ -43,7 +43,7 @@ void syslog(int priority, const char *fmt, ...)
 	va_end(ap);
 
 	while ((pos = strstr(str, "%1")) != NULL) {
-		str = realloc(str, ++str_len + 1);
+		str = realloc(str, st_add(++str_len, 1));
 		if (!str) {
 			warning("realloc failed: '%s'", strerror(errno));
 			return;