From 447c9303942c439a117d9b76ce6d6e2116b38ee7 Mon Sep 17 00:00:00 2001 From: Asim Viladi Oglu Manizada Date: Wed, 12 Aug 2026 01:21:53 +0000 Subject: [PATCH] net: tun: bound receive headroom tun_get_user() uses tun->align both as skb headroom and when choosing how much packet data to keep linear. OVS can propagate an oversized headroom request from another port to TUN or TAP. When align is larger than the usable space in a one-page skb head, SKB_MAX_HEAD(align) underflows and the result becomes negative when stored in good_linear. That value later wraps when assigned to the size_t linear variable, and tun_alloc_skb() can place skb->data outside the allocated head. Bound the headroom stored by TUN to the one-page skb-head budget and the largest non-sentinel 16-bit skb header offset. Leave one linear byte for raw TUN and a complete Ethernet header for TAP, including NET_IP_ALIGN. Also pull the raw-TUN protocol byte and the TAP Ethernet header before accessing them, so these checks remain safe for nonlinear skbs supplied by other allocation paths. Fixes: eaea34b23c46 ("net/tun: implement ndo_set_rx_headroom") Cc: stable@vger.kernel.org Signed-off-by: Asim Viladi Oglu Manizada Reviewed-by: Willem de Bruijn Link: https://patch.msgid.link/20260812012139.2134643-1-manizada@pm.me Signed-off-by: Jakub Kicinski --- drivers/net/tun.c | 21 ++++++++++++++++----- 1 file changed, 16 insertions(+), 5 deletions(-) diff --git a/drivers/net/tun.c b/drivers/net/tun.c index fed9dfdfcc3b..5bbe3123979e 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -1107,11 +1107,16 @@ static netdev_features_t tun_net_fix_features(struct net_device *dev, static void tun_set_headroom(struct net_device *dev, int new_hr) { struct tun_struct *tun = netdev_priv(dev); + size_t max_headroom; - if (new_hr < NET_SKB_PAD) - new_hr = NET_SKB_PAD; + max_headroom = min_t(size_t, SKB_MAX_HEAD(0), U16_MAX - 1); - tun->align = new_hr; + if ((tun->flags & TUN_TYPE_MASK) == IFF_TAP) + max_headroom -= ETH_HLEN + NET_IP_ALIGN; + else + max_headroom -= 1; + + tun->align = clamp_t(int, new_hr, NET_SKB_PAD, max_headroom); } static void @@ -1822,7 +1827,13 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile, switch (tun->flags & TUN_TYPE_MASK) { case IFF_TUN: if (tun->flags & IFF_NO_PI) { - u8 ip_version = skb->len ? (skb->data[0] >> 4) : 0; + u8 ip_version; + + if (!pskb_may_pull(skb, 1)) { + err = -EINVAL; + goto drop; + } + ip_version = skb->data[0] >> 4; switch (ip_version) { case 4: @@ -1842,7 +1853,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile, skb->dev = tun->dev; break; case IFF_TAP: - if (frags && !pskb_may_pull(skb, ETH_HLEN)) { + if (!pskb_may_pull(skb, ETH_HLEN)) { err = -ENOMEM; drop_reason = SKB_DROP_REASON_HDR_TRUNC; goto drop;