[PATCH] tcp: fix compiler array bounds warning on selective_acks[]

[Bjorn Helgaas]

With -Werror=array-bounds, gcc v4.8.x warns that in tcp_sack_remove(), a
selective_acks[] "array subscript is above array bounds".

I don't understand how gcc figures this out, or why we don't see similar
problems many other places, but this is the only fix I can figure out.

Signed-off-by: Bjorn Helgaas <bhelgaas@xxxxxxxxxx>
---
 net/ipv4/tcp_input.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 65cf90e063d5..65133b108236 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4047,7 +4047,8 @@ static void tcp_sack_remove(struct tcp_sock *tp)
 
 			/* Zap this SACK, by moving forward any other SACKS. */
 			for (i = this_sack+1; i < num_sacks; i++)
-				tp->selective_acks[i-1] = tp->selective_acks[i];
+				if (i < ARRAY_SIZE(tp->selective_acks))
+					tp->selective_acks[i-1] = tp->selective_acks[i];
 			num_sacks--;
 			continue;
 		}

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