libceph: replace overzealous BUG_ON in osdmap_apply_incremental()

If the osdmap is (maliciously) corrupted such that the incremental
osdmap epoch is different from what is expected, there is no need to
BUG.  Instead, just declare the incremental osdmap to be invalid.

Cc: stable@vger.kernel.org
Reported-by: ziming zhang <ezrakiez@gmail.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

Author: idryomov

net/ceph/osdmap.c

@@ -1979,11 +1979,13 @@ struct ceph_osdmap *osdmap_apply_incremental(void **p, void *end, bool msgr2,
 			 sizeof(u64) + sizeof(u32), e_inval);
 	ceph_decode_copy(p, &fsid, sizeof(fsid));
 	epoch = ceph_decode_32(p);
-	BUG_ON(epoch != map->epoch+1);
 	ceph_decode_copy(p, &modified, sizeof(modified));
 	new_pool_max = ceph_decode_64(p);
 	new_flags = ceph_decode_32(p);
 
+	if (epoch != map->epoch + 1)
+		goto e_inval;
+
 	/* full map? */
 	ceph_decode_32_safe(p, end, len, e_inval);
 	if (len > 0) {