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    SubjectRe: [RFC,PATCH 1/2] seccomp_filters: system call filtering using BPF
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    On Thu, Jan 12, 2012 at 8:50 AM, Oleg Nesterov <oleg@redhat.com> wrote:
    > On 01/11, Will Drewry wrote:
    >>
    >> This patch adds support for seccomp mode 2.  This mode enables dynamic
    >> enforcement of system call filtering policy in the kernel as specified
    >> by a userland task.  The policy is expressed in terms of a BPF program,
    >> as is used for userland-exposed socket filtering.  Instead of network
    >> data, the BPF program is evaluated over struct user_regs_struct at the
    >> time of the system call (as retrieved using regviews).
    >
    > Cool ;)
    >
    > I didn't really read this patch yet, just one nit.
    >
    >> +#define seccomp_filter_init_task(_tsk) do { \
    >> +     (_tsk)->seccomp.filter = NULL; \
    >> +} while (0);
    >
    > Cosmetic and subjective, but imho it would be better to add inline
    > functions instead of define's.

    Refactoring it a bit to make that possible. Since seccomp fork/init/free
    never needs access to the whole task_structs, I'll just pass in what's
    needed (and avoid the sched.h inclusion recursion).

    Comments on the next round will most definitely be appreciated!

    >> @@ -166,6 +167,7 @@ void free_task(struct task_struct *tsk)
    >>       free_thread_info(tsk->stack);
    >>       rt_mutex_debug_task_free(tsk);
    >>       ftrace_graph_exit_task(tsk);
    >> +     seccomp_filter_free_task(tsk);
    >>       free_task_struct(tsk);
    >>  }
    >>  EXPORT_SYMBOL(free_task);
    >> @@ -1209,6 +1211,7 @@ static struct task_struct *copy_process(unsigned long clone_flags,
    >>       /* Perform scheduler related setup. Assign this task to a CPU. */
    >>       sched_fork(p);
    >>
    >> +     seccomp_filter_init_task(p);
    >
    > This doesn't look right or I missed something. something seccomp_filter_init_task()
    > should be called right after dup_task_struct(), at least before copy process can
    > fail.
    >
    > Otherwise copy_process()->free_fork()->seccomp_filter_free_task() can put
    > current->seccomp.filter copied by arch_dup_task_struct().

    Ah - makes sense! I moved it under dup_task_struct before any goto's
    to bad_fork_free.

    >> +struct seccomp_filter {
    >> +     struct kref usage;
    >> +     struct pid *creator;
    >
    > Why? seccomp_filter->creator is never used, no?

    Removing it. It is from a related patch I'm experimenting with (adding
    optional tracehook support), but it has no bearing here.

    Thanks - new patch revision incoming!
    will
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