Commit af1f1ce2 authored Aug 03, 2023 by Andrew Kanner Committed by Greg Kroah-Hartman Aug 16, 2023

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 <jasowang@redhat.com> 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: 7df13219 ("tun: reserve extra headroom only when XDP is set")
Link: https://syzkaller.appspot.com/bug?extid=f817490f5bd20541b90a

Signed-off-by: Andrew Kanner <andrew.kanner@gmail.com>
Link: https://lore.kernel.org/r/20230803185947.2379988-1-andrew.kanner@gmail.com

Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 2bdc7f27

drivers/net/tun.c

+1 −1

Original line number	Original line	Diff line number	Diff line
	@@ -1654,7 +1654,7 @@ static bool tun_can_build_skb(struct tun_struct tun, struct tun_file tfile,
	if (zerocopy)		if (zerocopy)
	return false;		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)		SKB_DATA_ALIGN(sizeof(struct skb_shared_info)) > PAGE_SIZE)
	return false;		return false;