batman-adv: fix OOB read/write in network-coding decode

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>

diff --git a/net/batman-adv/network-coding.c b/net/batman-adv/network-coding.c
index 71ebd0284f95d229aa9ff4e9778c23354d51c856..0adc783fb83ca2ea6aed6928c64c6d540b34acd8 100644 (file)
--- a/net/batman-adv/network-coding.c
+++ b/net/batman-adv/network-coding.c
@@ -1687,7 +1687,12 @@ batadv_nc_skb_decode_packet(struct batadv_priv *bat_priv, struct sk_buff *skb,
 
        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: