[PATCH net v2] batman-adv: fix OOB read/write in network-coding decode

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 <redacted>
Signed-off-by: Stanislav Fort <redacted>
---
 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 9f56308779cc..af97d077369f 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:

-- 
2.39.3 (Apple Git-146)

On Sun, 31 Aug 2025 16:56:23 +0200, Stanislav Fort wrote:

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.

[...]

Applied, thanks!

[1/1] batman-adv: fix OOB read/write in network-coding decode
      https://git.open-mesh.org/linux-merge.git/commit/?h=batadv/net&id=d77b6ff0ce35a6d0b0b7b9581bc3f76d041d4087

Best regards,
-- 
Sven Eckelmann [off-list ref]