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>

4 files changed, 86 insertions, 8 deletions

diff --git a/libglusterfs/src/common-utils.c b/libglusterfs/src/common-utils.c
index 5015d9666b6..e5e08909ac7 100644
--- a/libglusterfs/src/common-utils.c
+++ b/libglusterfs/src/common-utils.c
@@ -30,6 +30,7 @@
 #include <signal.h>
 #include <assert.h>
 #include <libgen.h> /* for dirname() */
+#include <grp.h>
 
 #if defined(GF_BSD_HOST_OS) || defined(GF_DARWIN_HOST_OS)
 #include <sys/sysctl.h>
@@ -4877,3 +4878,75 @@ close_fds_except (int *fdv, size_t count)
 #endif /* !GF_LINUX_HOST_OS */
         return 0;
 }
+
+/**
+ * gf_getgrouplist - get list of groups to which a user belongs
+ *
+ * A convenience wrapper for getgrouplist(3).
+ *
+ * @param user - same as in getgrouplist(3)
+ * @param group - same as in getgrouplist(3)
+ * @param groups - pointer to a gid_t pointer
+ *
+ * gf_getgrouplist allocates a gid_t buffer which is big enough to
+ * hold the list of auxiliary group ids for user, up to the GF_MAX_AUX_GROUPS
+ * threshold. Upon succesfull invocation groups will be pointed to that buffer.
+ *
+ * @return success: the number of auxiliary group ids retrieved
+ *         failure: -1
+ */
+int
+gf_getgrouplist (const char *user, gid_t group, gid_t **groups)
+{
+        int ret     = -1;
+        int ngroups = SMALL_GROUP_COUNT;
+
+        *groups = GF_CALLOC (sizeof (gid_t), ngroups, gf_common_mt_groups_t);
+        if (!*groups)
+                return -1;
+
+        /*
+         * We are running getgrouplist() in a loop until we succeed (or hit
+         * certain exit conditions, see the comments below). This is because
+         * the indicated number of auxiliary groups that we obtain in case of
+         * the failure of the first invocation is not guaranteed to keep its
+         * validity upon the next invocation with a gid buffer of that size.
+         */
+        for (;;) {
+                int ngroups_old = ngroups;
+                ret = getgrouplist (user, group, *groups, &ngroups);
+                if (ret != -1)
+                        break;
+
+                if (ngroups >= GF_MAX_AUX_GROUPS) {
+                        /*
+                         * This should not happen as GF_MAX_AUX_GROUPS is set
+                         * to the max value of number of supported auxiliary
+                         * groups across all platforms supported by GlusterFS.
+                         * However, if it still happened some way, we wouldn't
+                         * care about the incompleteness of the result, we'd
+                         * just go on with what we got.
+                         */
+                        return GF_MAX_AUX_GROUPS;
+                } else if (ngroups <= ngroups_old) {
+                        /*
+                         * There is an edge case that getgrouplist() fails but
+                         * ngroups remains the same. This is actually not
+                         * specified in getgrouplist(3), but implementations
+                         * can do this upon internal failure[1]. To avoid
+                         * falling into an infinite loop when this happens, we
+                         * break the loop if the getgrouplist call failed
+                         * without an increase in the indicated group number.
+                         *
+                         * [1] https://sourceware.org/git/?p=glibc.git;a=blob;f=grp/initgroups.c;hb=refs/heads/release/2.25/master#l168
+                         */
+                        GF_FREE (*groups);
+                        return -1;
+                }
+
+                *groups = GF_REALLOC (*groups, ngroups * sizeof (gid_t));
+                if (!*groups)
+                        return -1;
+        }
+        return ret;
+}
diff --git a/libglusterfs/src/common-utils.h b/libglusterfs/src/common-utils.h
index c3c5ec77350..6a260c090c8 100644
--- a/libglusterfs/src/common-utils.h
+++ b/libglusterfs/src/common-utils.h
@@ -918,4 +918,7 @@ get_ip_from_addrinfo (struct addrinfo *addr, char **ip);
 
 int
 close_fds_except (int *fdv, size_t count);
+
+int
+gf_getgrouplist (const char *user, gid_t group, gid_t **groups);
 #endif /* _COMMON_UTILS_H */
diff --git a/libglusterfs/src/glusterfs.h b/libglusterfs/src/glusterfs.h
index ee5c21d43d5..2cd1f363b3b 100644
--- a/libglusterfs/src/glusterfs.h
+++ b/libglusterfs/src/glusterfs.h
@@ -235,9 +235,6 @@
 #define GF_REPLICATE_TRASH_DIR           ".landfill"
 
 /* GlusterFS's maximum supported Auxiliary GIDs */
-/* TODO: Keeping it to 200, so that we can fit in 2KB buffer for auth data
- * in RPC server code, if there is ever need for having more aux-gids, then
- * we have to add aux-gid in payload of actors */
 #define GF_MAX_AUX_GROUPS   65535
 
 #define GF_UUID_BUF_SIZE 50
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;
 }