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    SubjectRe: [PATCH v11 06/12] seccomp: add system call filtering using BPF
    Hello Will.

    I missed the previous discussions, and I don't think I can read
    all these emails now. So I apologize in advance if this was already
    discussed.

    On 02/24, Will Drewry wrote:
    >
    > struct seccomp {
    > int mode;
    > + struct seccomp_filter *filter;
    > };

    Minor nit, it seems that the new member can be "ifdef CONFIG_SECCOMP_FILTER"

    > +static long seccomp_attach_filter(struct sock_fprog *fprog)
    > +{
    > + struct seccomp_filter *filter;
    > + unsigned long fp_size = fprog->len * sizeof(struct sock_filter);
    > + long ret;
    > +
    > + if (fprog->len == 0 || fprog->len > BPF_MAXINSNS)
    > + return -EINVAL;

    OK, this limits the memory PR_SET_SECCOMP can use.

    But,

    > + /*
    > + * If there is an existing filter, make it the prev and don't drop its
    > + * task reference.
    > + */
    > + filter->prev = current->seccomp.filter;
    > + current->seccomp.filter = filter;
    > + return 0;

    this doesn't limit the number of filters, looks like a DoS.

    What if the application simply does prctl(PR_SET_SECCOMP, dummy_filter)
    in an endless loop?



    > +static struct seccomp_filter *get_seccomp_filter(struct seccomp_filter *orig)
    > +{
    > + if (!orig)
    > + return NULL;
    > + /* Reference count is bounded by the number of total processes. */
    > + atomic_inc(&orig->usage);
    > + return orig;
    > +}
    > ...
    > +void copy_seccomp(struct seccomp *child, const struct seccomp *parent)
    > +{
    > + /* Other fields are handled by dup_task_struct. */
    > + child->filter = get_seccomp_filter(parent->filter);
    > +}

    This is purely cosmetic, but imho looks a bit confusing.

    We do not copy seccomp->mode and this is correct, it was already copied
    implicitely. So why do we copy ->filter? This is not "symmetrical", afaics
    you can simply do

    void copy_seccomp(struct seccomp *child)
    {
    if (child->filter)
    atomic_inc(child->filter->usage);

    But once again, this is cosmetic, feel free to ignore.

    Oleg.



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