groups: don't allocate auxiliary gid list on stack

When glusterfs wants to retrieve the list of auxiliary gids
of a user, it typically allocates a sufficiently big gid_t
array on stack and calls getgrouplist(3) with it. However,
"sufficiently big" means to be of maximum supported gid list
size, which in GlusterFS is GF_MAX_AUX_GROUPS = 64k.
That means a 64k * sizeof(gid_t) = 256k allocation, which is
big enough to overflow the stack in certain cases.

A further observation is that stack allocation of the gid list
brings no gain, as in all cases the content of the gid list
eventually gets copied over to a heap allocated buffer.

So we add a convenience wrapper of getgrouplist to libglusterfs
called gf_getgrouplist which calls getgrouplist with a sufficiently
big heap allocated buffer (it takes care of the allocation too).
We are porting all the getgrouplist invocations to gf_getgrouplist
and thus eliminate the huge stack allocation.

BUG: 1464327
Change-Id: Icea76d0d74dcf2f87d26cb299acc771ca3b32d2b
Signed-off-by: Csaba Henk <csaba@redhat.com>
Reviewed-on: https://review.gluster.org/17706
Smoke: Gluster Build System <jenkins@build.gluster.org>
Reviewed-by: Niels de Vos <ndevos@redhat.com>
Reviewed-by: Amar Tumballi <amarts@redhat.com>
CentOS-regression: Gluster Build System <jenkins@build.gluster.org>

1 files changed, 10 insertions, 5 deletions

diff --git a/libglusterfs/src/stack.h b/libglusterfs/src/stack.h
index 20fbdfabff5..eb5848e92aa 100644
--- a/libglusterfs/src/stack.h
+++ b/libglusterfs/src/stack.h
@@ -357,21 +357,26 @@ STACK_RESET (call_stack_t *stack)
         } while (0)
 
 
+static void
+call_stack_set_groups (call_stack_t *stack, int ngrps, gid_t *groupbuf)
+{
+        stack->groups = groupbuf;
+        stack->ngrps = ngrps;
+}
+
 static inline int
 call_stack_alloc_groups (call_stack_t *stack, int ngrps)
 {
 	if (ngrps <= SMALL_GROUP_COUNT) {
-		stack->groups = stack->groups_small;
+		call_stack_set_groups (stack, ngrps, stack->groups_small);
 	} else {
-		stack->groups_large = GF_CALLOC (sizeof (gid_t), ngrps,
+		stack->groups_large = GF_CALLOC (ngrps, sizeof (gid_t),
 						 gf_common_mt_groups_t);
 		if (!stack->groups_large)
 			return -1;
-		stack->groups = stack->groups_large;
+		call_stack_set_groups (stack, ngrps, stack->groups_large);
 	}
 
-	stack->ngrps = ngrps;
-
 	return 0;
 }