[PATCH 4.9 52/90] batman-adv: Fix transmission of final, 16th fragment

[Greg Kroah-Hartman]

From: Linus Lü <linus.luessing@xxxxxxxxx>

commit 51c6b429c0c95e67edd1cb0b548c5cf6a6604763 upstream.

Trying to split and transmit a unicast packet in 16 parts will fail for
the final fragment: After having sent the 15th one with a frag_packet.no
index of 14, we will increase the the index to 15 - and return with an
error code immediately, even though one more fragment is due for
transmission and allowed.

Fixing this issue by moving the check before incrementing the index.

While at it, adding an unlikely(), because the check is actually more of
an assertion.

Fixes: ee75ed88879a ("batman-adv: Fragment and send skbs larger than mtu")
Signed-off-by: Linus Lü <linus.luessing@xxxxxxxxx>
Signed-off-by: Sven Eckelmann <sven@xxxxxxxxxxxxx>
Signed-off-by: Simon Wunderlich <sw@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 net/batman-adv/fragmentation.c |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

--- a/net/batman-adv/fragmentation.c
+++ b/net/batman-adv/fragmentation.c
@@ -490,6 +490,12 @@ int batadv_frag_send_packet(struct sk_bu
 
 	/* Eat and send fragments from the tail of skb */
 	while (skb->len > max_fragment_size) {
+		/* The initial check in this function should cover this case */
+		if (frag_header.no == BATADV_FRAG_MAX_FRAGMENTS - 1) {
+			ret = -1;
+			goto out;
+		}
+
 		skb_fragment = batadv_frag_create(skb, &frag_header, mtu);
 		if (!skb_fragment)
 			goto out;
@@ -507,12 +513,6 @@ int batadv_frag_send_packet(struct sk_bu
 		}
 
 		frag_header.no++;
-
-		/* The initial check in this function should cover this case */
-		if (frag_header.no == BATADV_FRAG_MAX_FRAGMENTS - 1) {
-			ret = -1;
-			goto out;
-		}
 	}
 
 	/* Make room for the fragment header. */