ceph: improve error handling in ceph_mdsmap_decode

This patch makes the following improvements to the error handling
in the ceph_mdsmap_decode function:

- Add a NULL check for return value from kcalloc
- Make use of the variable err

Signed-off-by: Emil Goode <emilgoode@gmail.com>
Signed-off-by: Sage Weil <sage@inktank.com>

fs/ceph/mdsmap.c

@@ -138,6 +138,8 @@ struct ceph_mdsmap *ceph_mdsmap_decode(void **p, void *end)
 				m->m_info[mds].export_targets =
 					kcalloc(num_export_targets, sizeof(u32),
 						GFP_NOFS);
+				if (m->m_info[mds].export_targets == NULL)
+					goto badmem;
 				for (j = 0; j < num_export_targets; j++)
 					m->m_info[mds].export_targets[j] =
 					       ceph_decode_32(&pexport_targets);
@@ -170,7 +172,7 @@ bad:
 		       DUMP_PREFIX_OFFSET, 16, 1,
 		       start, end - start, true);
 	ceph_mdsmap_destroy(m);
-	return ERR_PTR(-EINVAL);
+	return ERR_PTR(err);
 }
 
 void ceph_mdsmap_destroy(struct ceph_mdsmap *m)