[SRU B/F/J/OEM-5.14/HWE-5.17] netfilter: nf_queue: do not allow packet truncation below transport header offset

Thadeu Lima de Souza Cascardo cascardo at canonical.com
Tue Aug 16 08:53:05 UTC 2022

From: Florian Westphal <fw at strlen.de>

Domingo Dirutigliano and Nicola Guerrera report kernel panic when
sending nf_queue verdict with 1-byte nfta_payload attribute.

The IP/IPv6 stack pulls the IP(v6) header from the packet after the
input hook.

If user truncates the packet below the header size, this skb_pull() will
result in a malformed skb (skb->len < 0).

Fixes: 7af4cc3fa158 ("[NETFILTER]: Add "nfnetlink_queue" netfilter queue handler over nfnetlink")
Reported-by: Domingo Dirutigliano <pwnzer0tt1 at proton.me>
Signed-off-by: Florian Westphal <fw at strlen.de>
Reviewed-by: Pablo Neira Ayuso <pablo at netfilter.org>
(cherry picked from commit 99a63d36cb3ed5ca3aa6fcb64cffbeaf3b0fb164)
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>
 net/netfilter/nfnetlink_queue.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/net/netfilter/nfnetlink_queue.c b/net/netfilter/nfnetlink_queue.c
index 28efb8393591..9a82f3fc50da 100644
--- a/net/netfilter/nfnetlink_queue.c
+++ b/net/netfilter/nfnetlink_queue.c
@@ -844,11 +844,16 @@ nfqnl_enqueue_packet(struct nf_queue_entry *entry, unsigned int queuenum)
 static int
-nfqnl_mangle(void *data, int data_len, struct nf_queue_entry *e, int diff)
+nfqnl_mangle(void *data, unsigned int data_len, struct nf_queue_entry *e, int diff)
 	struct sk_buff *nskb;
 	if (diff < 0) {
+		unsigned int min_len = skb_transport_offset(e->skb);
+		if (data_len < min_len)
+			return -EINVAL;
 		if (pskb_trim(e->skb, data_len))
 			return -ENOMEM;
 	} else if (diff > 0) {

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