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    SubjectRe: [PATCH v2 3/3] pppoatm: protect against freeing of vcc
    On Tue, Nov 27, 2012 at 07:28:43PM +0100, Krzysztof Mazur wrote:
    >
    > While reviewing your br2684 patch I also found that some ATM drivers does
    > not call ->pop() when ->send() fails, they should do:
    >
    > if (vcc->pop)
    > vcc->pop(vcc, skb);
    > else
    > dev_kfree_skb(skb);
    >
    > but some drivers just call dev_kfree_skb(skb).
    >
    > I think that we should add atm_pop() function that does that and fix all
    > drivers.
    >

    I'm sending a patch that implements that idea.

    Currently we need two arguments vcc and skb. However, we have reserved
    ATM_SKB(skb)->vcc in skb control block for keeping vcc
    and we can create single argument version vcc_pop(skb). In that case
    we need to move:

    ATM_SKB(skb)->vcc = vcc;

    from ATM drivers to functions that call atmdev_ops->send().

    Krzysiek
    -- >8 --
    Subject: [PATCH] atm: introduce vcc_pop_*()

    The atm drivers to free skb, that they got from ->send(), cannot just use
    dev_kfree_skb*(), but they must use something like:

    if (vcc->pop)
    vcc->pop(vcc, skb);
    else
    dev_kfree_skb_any(skb);

    When vcc->pop is non-NULL, but they must in such case call vcc->pop().
    This causes duplicated code in many drivers, and some drivers even forgot
    to call vcc->pop() in some error handling code.

    The new vcc_pop_*() functions are equivalent to dev_kfree_skb*().
    Currently we always use dev_kfree_skb_any() to free, because using
    other versions it's probably worthless optimization - in ->pop() we
    already use only dev_kfree_skb_any(). The other functions we added
    only to not loose information from converting existing code that
    uses some non-any dev_kfree_skb*() variants.

    Signed-off-by: Krzysztof Mazur <krzysiek@podlesie.net>
    ---
    include/linux/atmdev.h | 11 +++++++++++
    net/atm/common.c | 9 +++++++++
    2 files changed, 20 insertions(+)

    diff --git a/include/linux/atmdev.h b/include/linux/atmdev.h
    index c1da539..dedccad 100644
    --- a/include/linux/atmdev.h
    +++ b/include/linux/atmdev.h
    @@ -283,6 +283,17 @@ int atm_pcr_goal(const struct atm_trafprm *tp);

    void vcc_release_async(struct atm_vcc *vcc, int reply);

    +/*
    + * vcc_pop_*() functions should be used by ATM driver to free transmitted
    + * skbs - skbs that were sent to driver by atmdev_opt->send() function.
    + *
    + * We provide three functions that can be used in different contexts.
    + * See dev_kfree_skb*() documentation for details.
    + */
    +void vcc_pop_any(struct atm_vcc *vcc, struct sk_buff *skb);
    +#define vcc_pop(vcc, skb) vcc_pop_any(vcc, skb)
    +#define vcc_pop_irq(vcc, skb) vcc_pop_any(vcc, skb)
    +
    struct atm_ioctl {
    struct module *owner;
    /* A module reference is kept if appropriate over this call.
    diff --git a/net/atm/common.c b/net/atm/common.c
    index 806fc0a..ad9c77d 100644
    --- a/net/atm/common.c
    +++ b/net/atm/common.c
    @@ -654,6 +654,15 @@ out:
    return error;
    }

    +void vcc_pop_any(struct atm_vcc *vcc, struct sk_buff *skb)
    +{
    + if (vcc->pop)
    + vcc->pop(vcc, skb);
    + else
    + dev_kfree_skb_any(skb);
    +}
    +EXPORT_SYMBOL(vcc_pop_any);
    +
    unsigned int vcc_poll(struct file *file, struct socket *sock, poll_table *wait)
    {
    struct sock *sk = sock->sk;
    --
    1.8.0.411.g71a7da8


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