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Commit 26989c9d authored by Willem de Bruijn's avatar Willem de Bruijn Committed by Greg Kroah-Hartman
Browse files

tun: read vnet_hdr_sz once 



[ Upstream commit e1edab87faf6ca30cd137e0795bc73aa9a9a22ec ]

When IFF_VNET_HDR is enabled, a virtio_net header must precede data.
Data length is verified to be greater than or equal to expected header
length tun->vnet_hdr_sz before copying.

Read this value once and cache locally, as it can be updated between
the test and use (TOCTOU).

Signed-off-by: default avatarWillem de Bruijn <willemb@google.com>
Reported-by: default avatarDmitry Vyukov <dvyukov@google.com>
CC: Eric Dumazet <edumazet@google.com>
Acked-by: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 0f895f51

drivers/net/tun.c

+6 −4
Original line number Diff line number Diff line
@@ -1187,9 +1187,11 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile, 
	}



	if (tun->flags & IFF_VNET_HDR) {

		if (len < tun->vnet_hdr_sz)

		int vnet_hdr_sz = READ_ONCE(tun->vnet_hdr_sz);



		if (len < vnet_hdr_sz)

			return -EINVAL;

		len -= tun->vnet_hdr_sz;

		len -= vnet_hdr_sz;



		n = copy_from_iter(&gso, sizeof(gso), from);

		if (n != sizeof(gso))
@@ -1201,7 +1203,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile, 


		if (tun16_to_cpu(tun, gso.hdr_len) > len)

			return -EINVAL;

		iov_iter_advance(from, tun->vnet_hdr_sz - sizeof(gso));

		iov_iter_advance(from, vnet_hdr_sz - sizeof(gso));

	}



	if ((tun->flags & TUN_TYPE_MASK) == IFF_TAP) {
@@ -1348,7 +1350,7 @@ static ssize_t tun_put_user(struct tun_struct *tun, 
		vlan_hlen = VLAN_HLEN;



	if (tun->flags & IFF_VNET_HDR)

		vnet_hdr_sz = tun->vnet_hdr_sz;

		vnet_hdr_sz = READ_ONCE(tun->vnet_hdr_sz);



	total = skb->len + vlan_hlen + vnet_hdr_sz;