don't reject unknown/future flags in sigaltstack, allow SS_AUTODISARM
historically, and likely accidentally, sigaltstack was specified to
fail with EINVAL if any flag bit other than SS_DISABLE was set. the
resolution of Austin Group issue 1187 fixes this so that the
requirement is only to fail for SS_ONSTACK (which cannot be set) or
"invalid" flags.
Linux fails on the kernel side for invalid flags, but historically
accepts SS_ONSTACK as a no-op, so it needs to be rejected in userspace
still.
with this change, the Linux-specific SS_AUTODISARM, provided since
commit 9680e1d03a794b0e0d5815c749478228ed40a36d but unusable due to
rejection at runtime, is now usable.
diff --git a/src/signal/sigaltstack.c b/src/signal/sigaltstack.c
index 62cb81a..cfa3f5c 100644
--- a/src/signal/sigaltstack.c
+++ b/src/signal/sigaltstack.c
@@ -9,7 +9,7 @@
errno = ENOMEM;
return -1;
}
- if (ss->ss_flags & ~SS_DISABLE) {
+ if (ss->ss_flags & SS_ONSTACK) {
errno = EINVAL;
return -1;
}