tun: free page on short-frame rejection in tun_xdp_one()

tun_xdp_one() returns -EINVAL on a frame shorter than ETH_HLEN without
freeing the page that vhost_net_build_xdp() allocated for it.
tun_sendmsg() discards that -EINVAL and still returns total_len, so
vhost_tx_batch() takes the success path and never frees the page; each
short frame in a batch leaks one page-frag chunk.

A local process that can open /dev/net/tun and /dev/vhost-net can hit
this path: it attaches a tun/tap device as the vhost-net backend and
feeds TX descriptors whose length minus the virtio-net header is below
ETH_HLEN. Each kick leaks the page-frag chunks for that batch, and a
tight submission loop exhausts host memory and triggers an OOM panic.
Free the page before returning -EINVAL, matching the XDP-program error
path in the same function.

Fixes: 049584807f1d ("tun: add missing verification for short frame")
Reported-by: Xiang Mei <xmei5@asu.edu>
Signed-off-by: Weiming Shi <bestswngs@gmail.com>
Reviewed-by: Dongli Zhang <dongli.zhang@oracle.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Link: https://patch.msgid.link/20260520160020.375349-2-bestswngs@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

diff --git a/drivers/net/tun.c b/drivers/net/tun.c
index b183189f185354051bded95f43bd77ee4f7cde24..f594360d66d653a5f30912d92b7946919f9df2e3 100644 (file)
--- a/drivers/net/tun.c
+++ b/drivers/net/tun.c
@@ -2394,8 +2394,10 @@ static int tun_xdp_one(struct tun_struct *tun,
        bool skb_xdp = false;
        struct page *page;
 
-       if (unlikely(datasize < ETH_HLEN))
+       if (unlikely(datasize < ETH_HLEN)) {
+               put_page(virt_to_head_page(xdp->data));
                return -EINVAL;
+       }
 
        xdp_prog = rcu_dereference(tun->xdp_prog);
        if (xdp_prog) {