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);
 }