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    Subject[PATCH 3.2 191/199] tun: read vnet_hdr_sz once
    3.2.87-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Willem de Bruijn <willemb@google.com>

    [ 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: Willem de Bruijn <willemb@google.com>
    Reported-by: Dmitry Vyukov <dvyukov@google.com>
    CC: Eric Dumazet <edumazet@google.com>
    Acked-by: Eric Dumazet <edumazet@google.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    [bwh: Backported to 3.2:
    - Use ACCESS_ONCE() instead of READ_ONCE()
    - Adjust context]
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    drivers/net/tun.c | 10 ++++++----
    1 file changed, 6 insertions(+), 4 deletions(-)

    --- a/drivers/net/tun.c
    +++ b/drivers/net/tun.c
    @@ -625,9 +625,11 @@ static ssize_t tun_get_user(struct tun_s
    }

    if (tun->flags & TUN_VNET_HDR) {
    - if (len < tun->vnet_hdr_sz)
    + int vnet_hdr_sz = ACCESS_ONCE(tun->vnet_hdr_sz);
    +
    + if (len < vnet_hdr_sz)
    return -EINVAL;
    - len -= tun->vnet_hdr_sz;
    + len -= vnet_hdr_sz;

    if (memcpy_fromiovecend((void *)&gso, iv, offset, sizeof(gso)))
    return -EFAULT;
    @@ -638,7 +640,7 @@ static ssize_t tun_get_user(struct tun_s

    if (gso.hdr_len > len)
    return -EINVAL;
    - offset += tun->vnet_hdr_sz;
    + offset += vnet_hdr_sz;
    }

    if ((tun->flags & TUN_TYPE_MASK) == TUN_TAP_DEV) {
    @@ -770,7 +772,7 @@ static ssize_t tun_put_user(struct tun_s
    int vnet_hdr_sz = 0;

    if (tun->flags & TUN_VNET_HDR)
    - vnet_hdr_sz = tun->vnet_hdr_sz;
    + vnet_hdr_sz = ACCESS_ONCE(tun->vnet_hdr_sz);

    if (!(tun->flags & TUN_NO_PI)) {
    if ((len -= sizeof(pi)) < 0)
    \
     
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      Last update: 2017-03-10 13:33    [W:2.443 / U:0.096 seconds]
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