[PATCH 5.4 22/45] batman-adv: fix OOB read/write in network-coding decode

[Greg Kroah-Hartman <gregkh@linuxfoundation.org>]

5.4-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Stanislav Fort <stanislav.fort@aisle.com>

commit d77b6ff0ce35a6d0b0b7b9581bc3f76d041d4087 upstream.

batadv_nc_skb_decode_packet() trusts coded_len and checks only against
skb->len. XOR starts at sizeof(struct batadv_unicast_packet), reducing
payload headroom, and the source skb length is not verified, allowing an
out-of-bounds read and a small out-of-bounds write.

Validate that coded_len fits within the payload area of both destination
and source sk_buffs before XORing.

Fixes: 2df5278b0267 ("batman-adv: network coding - receive coded packets and decode them")
Cc: stable@vger.kernel.org
Reported-by: Stanislav Fort <disclosure@aisle.com>
Signed-off-by: Stanislav Fort <stanislav.fort@aisle.com>
Signed-off-by: Sven Eckelmann <sven@narfation.org>
Signed-off-by: Simon Wunderlich <sw@simonwunderlich.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 net/batman-adv/network-coding.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/net/batman-adv/network-coding.c
+++ b/net/batman-adv/network-coding.c
@@ -1694,7 +1694,12 @@ batadv_nc_skb_decode_packet(struct batad
 
 	coding_len = ntohs(coded_packet_tmp.coded_len);
 
-	if (coding_len > skb->len)
+	/* ensure dst buffer is large enough (payload only) */
+	if (coding_len + h_size > skb->len)
+		return NULL;
+
+	/* ensure src buffer is large enough (payload only) */
+	if (coding_len + h_size > nc_packet->skb->len)
 		return NULL;
 
 	/* Here the magic is reversed: