tun_put_user() declares an on-stack struct virtio_net_hdr_v1_hash_tunnel without zeroing it. For a non-tunnel skb, virtio_net_hdr_tnl_from_skb() only initializes the first 10 bytes (sizeof(struct virtio_net_hdr)), leaving bytes 10..23 (num_buffers and the hash/tunnel fields) as stack garbage. An unprivileged user can set the vnet header size to 24 with TUNSETVNETHDRSZ, so __tun_vnet_hdr_put() copies all 24 bytes of the partially-initialized struct to userspace, leaking 14 bytes of kernel stack on every read of a non-tunnel packet. Fix it the same way tun_get_user() already does by zeroing the whole header right after declaration. Fixes: 288f30435132 ("tun: enable gso over UDP tunnel support.") Reported-by: Weiming Shi Assisted-by: Claude:claude-opus-4-8 Signed-off-by: Xiang Mei --- drivers/net/tun.c | 1 + 1 file changed, 1 insertion(+) diff --git a/drivers/net/tun.c b/drivers/net/tun.c index 9e7744eb57a3..fed9dfdfcc3b 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -2070,6 +2070,7 @@ static ssize_t tun_put_user(struct tun_struct *tun, struct virtio_net_hdr_v1_hash_tunnel hdr; struct virtio_net_hdr *gso; + memset(&hdr, 0, sizeof(hdr)); ret = tun_vnet_hdr_tnl_from_skb(tun->flags, tun->dev, skb, &hdr); if (ret) -- 2.43.0