From: Sven Eckelmann <[email protected]> batadv_frag_skb_buffer() is called by batadv_batman_skb_recv() when a BATADV_UNICAST_FRAG packet is received. Once all fragments are collected and the packet is reassembled, batadv_recv_frag_packet() calls batadv_batman_skb_recv() again to process the defragmented payload.
A malicious sender can craft a BATADV_UNICAST_FRAG packet whose reassembled payload is itself a BATADV_UNICAST_FRAG packet (matryoshka-style nesting). Each nesting level recurses through batadv_batman_skb_recv() without bound, growing the kernel stack until it is exhausted. Since refragmentation or fragments in fragments are not actually allowed, discard all packets which are still BATADV_UNICAST_FRAG packets after the defragmentation process. Cc: [email protected] Fixes: 610bfc6bc99b ("batman-adv: Receive fragmented packets and merge") Reported-by: Yuan Tan <[email protected]> Reported-by: Yifan Wu <[email protected]> Reported-by: Juefei Pu <[email protected]> Reported-by: Xin Liu <[email protected]> Reviewed-by: Yuan Tan <[email protected]> Signed-off-by: Sven Eckelmann <[email protected]> Signed-off-by: Simon Wunderlich <[email protected]> --- net/batman-adv/fragmentation.c | 35 ++++++++++++++++++++++++++++++++++ 1 file changed, 35 insertions(+) diff --git a/net/batman-adv/fragmentation.c b/net/batman-adv/fragmentation.c index 1152c2ce0c1ea..4a594aa2ebf66 100644 --- a/net/batman-adv/fragmentation.c +++ b/net/batman-adv/fragmentation.c @@ -304,6 +304,31 @@ batadv_frag_merge_packets(struct hlist_head *chain) return skb_out; } +/** + * batadv_skb_is_frag() - check if newly merged skb is gain a unicast packet + * @skb: newly merged skb + * + * Return: if newly skb is of type BATADV_UNICAST_FRAG + */ +static bool batadv_skb_is_frag(struct sk_buff *skb) +{ + struct batadv_ogm_packet *batadv_ogm_packet; + + /* packet should hold at least type and version */ + if (unlikely(!pskb_may_pull(skb, 2))) + return false; + + batadv_ogm_packet = (struct batadv_ogm_packet *)skb->data; + + if (batadv_ogm_packet->version != BATADV_COMPAT_VERSION) + return false; + + if (batadv_ogm_packet->packet_type != BATADV_UNICAST_FRAG) + return false; + + return true; +} + /** * batadv_frag_skb_buffer() - buffer fragment for later merge * @skb: skb to buffer @@ -337,6 +362,16 @@ bool batadv_frag_skb_buffer(struct sk_buff **skb, if (!skb_out) goto out_err; + /* fragment in fragment is not allowed. otherwise it is possible + * to exhaust the stack when receiving a matryoshka-style + * "fragments in a fragment packet" + */ + if (batadv_skb_is_frag(skb_out)) { + kfree_skb(skb_out); + skb_out = NULL; + goto out_err; + } + out: ret = true; out_err: -- 2.47.3
