getgrent_next_nss (compat-initgroups): Remove alloca fallback [BZ #18023]

If the caller-supplied buffer is not large enough, fall back directly
malloc.

The previous __libc_use_alloca check was incorrect because it did not
take into account that extend_alloca may fail to merge allocations, so
it would underestimate the stack space being used by roughly a factor
of two.

1 files changed, 6 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index 1cafbb1..6241a63 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,6 +1,12 @@
 2018-06-25  Florian Weimer  <fweimer@redhat.com>
 
 	[BZ #18023]
+	* nss/nss_compat/compat-initgroups.c (getgrent_next_nss): Fall
+	back to malloc directly, without stack allocations.
+
+2018-06-25  Florian Weimer  <fweimer@redhat.com>
+
+	[BZ #18023]
 	* nscd/aicache.c (addhstaiX): Use struct scratch_buffer instead
 	of extend_alloca.