From f12c2de4f542e3220e17e0606f492110064f04cb Mon Sep 17 00:00:00 2001 From: Kyle Zeng Date: Mon, 17 Aug 2026 08:49:54 +0000 Subject: [PATCH] batman-adv: reject unrepresentable multicast TVLV offsets The network and transport header fields in struct sk_buff are 16-bit offsets from skb->head, and U16_MAX is reserved as the unset transport header value. batadv_tvlv_call_handler() sets both fields from a received multicast TVLV without checking whether the TVLV end is representable. If the end offset exceeds the field's range, skb_set_transport_header() truncates it so that the transport header precedes the network header. The negative difference is then returned by skb_network_header_len() as a large u32. batadv_mcast_forw_packet() consequently accepts an oversized multicast tracker and accesses memory beyond the skb data. Add skb_set_transport_header_careful(), an offset-aware counterpart to skb_reset_transport_header_careful(), which validates the final head-relative offset before assigning it. Use the new helper in batadv_tvlv_call_handler() and reject unrepresentable TVLVs before setting the network header. Fixes: 07afe1ba288c ("batman-adv: mcast: implement multicast packet reception and forwarding") Cc: stable@vger.kernel.org Signed-off-by: Kyle Zeng Co-developed-by: David Lee Signed-off-by: David Lee Acked-by: Sven Eckelmann Link: https://patch.msgid.link/20260817084955.944189-1-david.lee@trailofbits.com Signed-off-by: Jakub Kicinski --- include/linux/skbuff.h | 24 ++++++++++++++++++++++++ net/batman-adv/tvlv.c | 5 ++++- 2 files changed, 28 insertions(+), 1 deletion(-) diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h index 95184183180f..5522716df8ff 100644 --- a/include/linux/skbuff.h +++ b/include/linux/skbuff.h @@ -3126,6 +3126,30 @@ static inline void skb_set_transport_header(struct sk_buff *skb, skb->transport_header += offset; } +/** + * skb_set_transport_header_careful - conditionally set transport header + * @skb: buffer to alter + * @offset: offset to add to skb->data + * + * Hardened version of skb_set_transport_header(). + * + * Returns: true if the operation was a success. + */ +static inline bool __must_check +skb_set_transport_header_careful(struct sk_buff *skb, const int offset) +{ + long thoff = skb->data - skb->head + offset; + + if (unlikely(thoff != (typeof(skb->transport_header))thoff)) + return false; + + if (unlikely(thoff == (typeof(skb->transport_header))~0U)) + return false; + + skb->transport_header = thoff; + return true; +} + static inline unsigned char *skb_network_header(const struct sk_buff *skb) { return skb->head + skb->network_header; diff --git a/net/batman-adv/tvlv.c b/net/batman-adv/tvlv.c index de907c07fa15..93492d393c34 100644 --- a/net/batman-adv/tvlv.c +++ b/net/batman-adv/tvlv.c @@ -438,8 +438,11 @@ static int batadv_tvlv_call_handler(struct batadv_priv *bat_priv, return NET_RX_SUCCESS; tvlv_offset = (unsigned char *)tvlv_value - skb->data; + if (!skb_set_transport_header_careful(skb, + tvlv_offset + tvlv_value_len)) + return -EINVAL; + skb_set_network_header(skb, tvlv_offset); - skb_set_transport_header(skb, tvlv_offset + tvlv_value_len); return tvlv_handler->mcast_handler(bat_priv, skb); }