From: Andrew Kanner Date: Thu, 3 Aug 2023 18:59:48 +0000 (+0200) Subject: drivers: net: prevent tun_build_skb() to exceed the packet size limit X-Git-Tag: v4.14.323~10 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=cb1ded0c577aaa502b15cbf4f6e479401000741e;p=thirdparty%2Fkernel%2Fstable.git drivers: net: prevent tun_build_skb() to exceed the packet size limit commit 59eeb232940515590de513b997539ef495faca9a upstream. Using the syzkaller repro with reduced packet size it was discovered that XDP_PACKET_HEADROOM is not checked in tun_can_build_skb(), although pad may be incremented in tun_build_skb(). This may end up with exceeding the PAGE_SIZE limit in tun_build_skb(). Jason Wang proposed to count XDP_PACKET_HEADROOM always (e.g. without rcu_access_pointer(tun->xdp_prog)) in tun_can_build_skb() since there's a window during which XDP program might be attached between tun_can_build_skb() and tun_build_skb(). Fixes: 7df13219d757 ("tun: reserve extra headroom only when XDP is set") Link: https://syzkaller.appspot.com/bug?extid=f817490f5bd20541b90a Signed-off-by: Andrew Kanner Link: https://lore.kernel.org/r/20230803185947.2379988-1-andrew.kanner@gmail.com Signed-off-by: Jakub Kicinski Signed-off-by: Greg Kroah-Hartman --- diff --git a/drivers/net/tun.c b/drivers/net/tun.c index b616961267d09..b62417a0c72d2 100644 --- a/drivers/net/tun.c +++ b/drivers/net/tun.c @@ -1275,7 +1275,7 @@ static bool tun_can_build_skb(struct tun_struct *tun, struct tun_file *tfile, if (zerocopy) return false; - if (SKB_DATA_ALIGN(len + TUN_RX_PAD) + + if (SKB_DATA_ALIGN(len + TUN_RX_PAD + XDP_PACKET_HEADROOM) + SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) > PAGE_SIZE) return false;