Fix bug with disabling sigaltstack()

Author: jart

libc/calls/sigaltstack.c

@@ -132,7 +132,8 @@ int sigaltstack(const struct sigaltstack *neu, struct sigaltstack *old) {
   if (neu && ((neu->ss_size >> 32) ||  //
               (neu->ss_flags & ~(SS_ONSTACK | SS_DISABLE)))) {
     rc = einval();
-  } else if (neu && neu->ss_size < __get_minsigstksz()) {
+  } else if (neu && !(neu->ss_flags & SS_DISABLE) &&
+             neu->ss_size < __get_minsigstksz()) {
     rc = enomem();
   } else if (IsLinux()) {
     rc = sys_sigaltstack(neu, old);

test/libc/calls/sigaltstack_test.c

@@ -0,0 +1,41 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│ vi: set et ft=c ts=2 sts=2 sw=2 fenc=utf-8                               :vi │
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2024 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/calls/struct/sigaltstack.h"
+#include "libc/calls/calls.h"
+#include "libc/errno.h"
+#include "libc/sysv/consts/ss.h"
+#include "libc/testlib/testlib.h"
+
+TEST(sigaltstack, badFlag) {
+  struct sigaltstack ss;
+  ss.ss_flags = -1;
+  ss.ss_size = 0;
+  ss.ss_sp = 0;
+  EXPECT_SYS(EINVAL, -1, sigaltstack(&ss, 0));
+}
+
+TEST(sigaltstack, disable) {
+  struct sigaltstack ss;
+  ss.ss_flags = SS_DISABLE;
+  ss.ss_size = 0;
+  ss.ss_sp = 0;
+  EXPECT_SYS(0, 0, sigaltstack(&ss, 0));
+  EXPECT_SYS(0, 0, sigaltstack(0, &ss));
+  EXPECT_EQ(SS_DISABLE, ss.ss_flags);
+}