Patch "batman-adv: Don't always reallocate the fragmentation skb head" has been added to the 5.4-stable tree

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    batman-adv: Don't always reallocate the fragmentation skb head

to the 5.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     batman-adv-don-t-always-reallocate-the-fragmentation-skb-head.patch
and it can be found in the queue-5.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@vger.kernel.org> know about it.


From foo@baz Tue Nov 23 01:32:30 PM CET 2021
From: Sven Eckelmann <sven@narfation.org>
Date: Sat, 20 Nov 2021 13:40:53 +0100
Subject: batman-adv: Don't always reallocate the fragmentation skb head
To: stable@vger.kernel.org
Cc: b.a.t.m.a.n@lists.open-mesh.org, Sven Eckelmann <sven@narfation.org>, Simon Wunderlich <sw@simonwunderlich.de>
Message-ID: <20211120124053.261156-4-sven@narfation.org>

From: Sven Eckelmann <sven@narfation.org>

commit 992b03b88e36254e26e9a4977ab948683e21bd9f upstream.

When a packet is fragmented by batman-adv, the original batman-adv header
is not modified. Only a new fragmentation is inserted between the original
one and the ethernet header. The code must therefore make sure that it has
a writable region of this size in the skbuff head.

But it is not useful to always reallocate the skbuff by this size even when
there would be more than enough headroom still in the skb. The reallocation
is just to costly during in this codepath.

Fixes: ee75ed88879a ("batman-adv: Fragment and send skbs larger than mtu")
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/batman-adv/fragmentation.c |   11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

--- a/net/batman-adv/fragmentation.c
+++ b/net/batman-adv/fragmentation.c
@@ -527,13 +527,14 @@ int batadv_frag_send_packet(struct sk_bu
 		frag_header.no++;
 	}
 
-	/* Make room for the fragment header. */
-	if (batadv_skb_head_push(skb, header_size) < 0 ||
-	    pskb_expand_head(skb, header_size + ETH_HLEN, 0, GFP_ATOMIC) < 0) {
-		ret = -ENOMEM;
+	/* make sure that there is at least enough head for the fragmentation
+	 * and ethernet headers
+	 */
+	ret = skb_cow_head(skb, ETH_HLEN + header_size);
+	if (ret < 0)
 		goto put_primary_if;
-	}
 
+	skb_push(skb, header_size);
 	memcpy(skb->data, &frag_header, header_size);
 
 	/* Send the last fragment */


Patches currently in stable-queue which might be from sven@narfation.org are

queue-5.4/batman-adv-consider-fragmentation-for-needed_headroom.patch
queue-5.4/batman-adv-reserve-needed_-room-for-fragments.patch
queue-5.4/batman-adv-don-t-always-reallocate-the-fragmentation-skb-head.patch