netdev - [PATCH net 1/1] batman-adv: fix OOB read/write in network-coding decode

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Message-ID: <20250901161546.1463690-2-sw@simonwunderlich.de>
Date: Mon,  1 Sep 2025 18:15:46 +0200
From: Simon Wunderlich <sw@...onwunderlich.de>
To: davem@...emloft.net,
	kuba@...nel.org
Cc: netdev@...r.kernel.org,
	b.a.t.m.a.n@...ts.open-mesh.org,
	Stanislav Fort <stanislav.fort@...le.com>,
	stable@...r.kernel.org,
	Stanislav Fort <disclosure@...le.com>,
	Sven Eckelmann <sven@...fation.org>,
	Simon Wunderlich <sw@...onwunderlich.de>
Subject: [PATCH net 1/1] batman-adv: fix OOB read/write in network-coding decode

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

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@...r.kernel.org
Reported-by: Stanislav Fort <disclosure@...le.com>
Signed-off-by: Stanislav Fort <stanislav.fort@...le.com>
Signed-off-by: Sven Eckelmann <sven@...fation.org>
Signed-off-by: Simon Wunderlich <sw@...onwunderlich.de>
---
 net/batman-adv/network-coding.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/net/batman-adv/network-coding.c b/net/batman-adv/network-coding.c
index 9f56308779cc3..af97d077369f9 100644
--- 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:
-- 
2.47.2