On Wed, Sep 27, 2017 at 5:25 PM, Tycho Andersen <tycho@xxxxxxxxxx> wrote:
> From: Oleg Nesterov <oleg@xxxxxxxxxx>
>
> As Chris explains, get_seccomp_filter() and put_seccomp_filter() can
> use the different filters, once we drop ->siglock task->seccomp.filter
> can be replaced by SECCOMP_FILTER_FLAG_TSYNC.
>
> v2: add __get_seccomp_filter vs. open coding refcount_inc()
>
> Fixes: f8e529ed941b ("seccomp, ptrace: add support for dumping seccomp filters")
> Reported-by: Chris Salls <chrissalls5@xxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Oleg Nesterov <oleg@xxxxxxxxxx>
> Signed-off-by: Tycho Andersen <tycho@xxxxxxxxxx>
Thanks, applied!
-Kees
> ---
> kernel/seccomp.c | 23 ++++++++++++++++-------
> 1 file changed, 16 insertions(+), 7 deletions(-)
>
> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
> index c24579dfa7a1..bb3a38005b9c 100644
> --- a/kernel/seccomp.c
> +++ b/kernel/seccomp.c
> @@ -473,14 +473,19 @@ static long seccomp_attach_filter(unsigned int flags,
> return 0;
> }
>
> +void __get_seccomp_filter(struct seccomp_filter *filter)
> +{
> + /* Reference count is bounded by the number of total processes. */
> + refcount_inc(&filter->usage);
> +}
> +
> /* get_seccomp_filter - increments the reference count of the filter on @tsk */
> void get_seccomp_filter(struct task_struct *tsk)
> {
> struct seccomp_filter *orig = tsk->seccomp.filter;
> if (!orig)
> return;
> - /* Reference count is bounded by the number of total processes. */
> - refcount_inc(&orig->usage);
> + __get_seccomp_filter(orig);
> }
>
> static inline void seccomp_filter_free(struct seccomp_filter *filter)
> @@ -491,10 +496,8 @@ static inline void seccomp_filter_free(struct seccomp_filter *filter)
> }
> }
>
> -/* put_seccomp_filter - decrements the ref count of tsk->seccomp.filter */
> -void put_seccomp_filter(struct task_struct *tsk)
> +static void __put_seccomp_filter(struct seccomp_filter *orig)
> {
> - struct seccomp_filter *orig = tsk->seccomp.filter;
> /* Clean up single-reference branches iteratively. */
> while (orig && refcount_dec_and_test(&orig->usage)) {
> struct seccomp_filter *freeme = orig;
> @@ -503,6 +506,12 @@ void put_seccomp_filter(struct task_struct *tsk)
> }
> }
>
> +/* put_seccomp_filter - decrements the ref count of tsk->seccomp.filter */
> +void put_seccomp_filter(struct task_struct *tsk)
> +{
> + __put_seccomp_filter(tsk->seccomp.filter);
> +}
> +
> static void seccomp_init_siginfo(siginfo_t *info, int syscall, int reason)
> {
> memset(info, 0, sizeof(*info));
> @@ -1025,13 +1034,13 @@ long seccomp_get_filter(struct task_struct *task, unsigned long filter_off,
> if (!data)
> goto out;
>
> - get_seccomp_filter(task);
> + __get_seccomp_filter(filter);
> spin_unlock_irq(&task->sighand->siglock);
>
> if (copy_to_user(data, fprog->filter, bpf_classic_proglen(fprog)))
> ret = -EFAULT;
>
> - put_seccomp_filter(task);
> + __put_seccomp_filter(filter);
> return ret;
>
> out:
> --
> 2.11.0
>
--
Kees Cook
Pixel Security