libbb: avoid malloc/free in bb_unsetenv()

function                                             old     new   delta
bb_unsetenv                                           55      83     +28

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 21 insertions, 13 deletions

diff --git a/libbb/xfuncs_printf.c b/libbb/xfuncs_printf.c
index 1b11caf6b..f569b0263 100644
--- a/libbb/xfuncs_printf.c
+++ b/libbb/xfuncs_printf.c
@@ -344,20 +344,28 @@ void FAST_FUNC xsetenv(const char *key, const char *value)
  */
 void FAST_FUNC bb_unsetenv(const char *var)
 {
-	char *tp = strchr(var, '=');
-
-	if (!tp) {
-		unsetenv(var);
-		return;
+	char onstack[128 - 16]; /* smaller stack setup code on x86 */
+	char *tp;
+
+	tp = strchr(var, '=');
+	if (tp) {
+		/* In case var was putenv'ed, we can't replace '='
+		 * with NUL and unsetenv(var) - it won't work,
+		 * env is modified by the replacement, unsetenv
+		 * sees "VAR" instead of "VAR=VAL" and does not remove it!
+		 * Horror :(
+		 */
+		unsigned sz = tp - var;
+		if (sz < sizeof(onstack)) {
+			((char*)mempcpy(onstack, var, sz))[0] = '\0';
+			tp = NULL;
+			var = onstack;
+		} else {
+			/* unlikely: very long var name */
+			var = tp = xstrndup(var, sz);
+		}
 	}
-
-	/* In case var was putenv'ed, we can't replace '='
-	 * with NUL and unsetenv(var) - it won't work,
-	 * env is modified by the replacement, unsetenv
-	 * sees "VAR" instead of "VAR=VAL" and does not remove it!
-	 * horror :( */
-	tp = xstrndup(var, tp - var);
-	unsetenv(tp);
+	unsetenv(var);
 	free(tp);
 }