[PATCH] net/xen-netback: Break build if netback slots > max_skbs + 1

[David Kahurani <k.kahurani@xxxxxxxxx>]

If XEN_NETBK_LEGACY_SLOTS_MAX and MAX_SKB_FRAGS have a difference of
more than 1, with MAX_SKB_FRAGS being the lesser value, it opens up a
path for null-dereference. It was also noted that some distributions
were modifying upstream behaviour in that direction which necessitates
this patch.

Signed-off-by: David Kahurani <k.kahurani@xxxxxxxxx>
---
 drivers/net/xen-netback/netback.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/net/xen-netback/netback.c 
b/drivers/net/xen-netback/netback.c
index 88f760a7cbc3..df032e33787f 100644
--- a/drivers/net/xen-netback/netback.c
+++ b/drivers/net/xen-netback/netback.c
@@ -1005,6 +1005,7 @@ static void xenvif_tx_build_gops(struct xenvif_queue 
*queue,
                        break;
                }
 
+               BUILD_BUG_ON(XEN_NETBK_LEGACY_SLOTS_MAX > MAX_SKB_FRAGS + 1);
                if (ret >= XEN_NETBK_LEGACY_SLOTS_MAX - 1 && data_len < 
txreq.size)
                        data_len = txreq.size;
 
-- 
2.25.1