c18n: Make stack resolution re-entrant

libexec/rtld-elf/rtld_c18n.c

@@ -699,6 +699,14 @@ allocate_rstk_impl(unsigned index)
 	unsigned cid_off;
 	size_t capacity, size;
 	struct stk_table *table;
+	sigset_t nset, oset;
+
+	/*
+	 * Make the function re-entrant by blocking all signals and re-check
+	 * whether the stack needs to be allocated.
+	 */
+	sigfillset(&nset);
+	sigprocmask(SIG_SETMASK, &nset, &oset);
 
 	table = stk_table_get();
 
@@ -710,8 +718,10 @@ allocate_rstk_impl(unsigned index)
 		capacity = MAX(capacity * 2, cid_off + 1);
 		table = stk_table_expand(table, capacity, true);
 		stk_table_set(table);
+	} else if (table->stacks[cid_off].size != 0) {
+		stk = table->stacks[cid_off].bottom;
+		goto finish;
 	}
-	assert(table->stacks[cid_off].size == 0);
 
 	size = C18N_STACK_SIZE;
 	stk = stk_create(size);
@@ -720,6 +730,9 @@ allocate_rstk_impl(unsigned index)
 	table->stacks[cid_off].bottom = stk;
 	table->stacks[cid_off].size = size;
 
+finish:
+	sigprocmask(SIG_SETMASK, &oset, NULL);
+
 	return (stk);
 }