ash: [EVAL] Fix use-after-free in dotrap/evalstring

From upstream:

    [EVAL] Fix use-after-free in dotrap/evalstring

    The function dotrap calls evalstring using the stored trap string.
    If evalstring then unsets that exact trap string then we will end
    up using freed memory.

    This patch fixes it by making evalstring always duplicate the string
    before using it.

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

1 files changed, 7 insertions, 3 deletions

diff --git a/shell/ash.c b/shell/ash.c
index f395a16..7a7ea18 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -1459,7 +1459,7 @@ stunalloc(void *p)
  * Like strdup but works with the ash stack.
  */
 static char *
-ststrdup(const char *p)
+sstrdup(const char *p)
 {
 	size_t len = strlen(p) + 1;
 	return memcpy(stalloc(len), p, len);
@@ -2514,7 +2514,7 @@ updatepwd(const char *dir)
 	char *cdcomppath;
 	const char *lim;
 
-	cdcomppath = ststrdup(dir);
+	cdcomppath = sstrdup(dir);
 	STARTSTACKSTR(new);
 	if (*dir != '/') {
 		if (curdir == nullstr)
@@ -6993,7 +6993,7 @@ addfname(const char *name)
 	struct strlist *sp;
 
 	sp = stzalloc(sizeof(*sp));
-	sp->text = ststrdup(name);
+	sp->text = sstrdup(name);
 	*exparg.lastp = sp;
 	exparg.lastp = &sp->next;
 }
@@ -12221,10 +12221,12 @@ evalstring(char *s, int mask)
 	int skip;
 //	int status;
 
+	s = sstrdup(s);
 	setinputstring(s);
 	setstackmark(&smark);
 
 	skip = 0;
+//	status = 0;
 	while ((n = parsecmd(0)) != NODE_EOF) {
 		int i;
 
@@ -12236,7 +12238,9 @@ evalstring(char *s, int mask)
 		if (skip)
 			break;
 	}
+	popstackmark(&smark);
 	popfile();
+	stunalloc(s);
 
 	skip &= mask;
 	evalskip = skip;