Re: [PATCH] ptrace, seccomp: add support for retrieving seccomp flags

From: Kees Cook
Date: Tue Sep 19 2017 - 16:08:34 EST

On Tue, Sep 19, 2017 at 10:47 AM, Tycho Andersen <tycho@xxxxxxxxxx> wrote:
> With the new SECCOMP_FILTER_FLAG_LOG, we need to be able to extract these
> flags for checkpoint restore, since they describe the state of a filter.
>
> So, let's add PTRACE_SECCOMP_GET_FLAGS, similar to ..._GET_FILTER, which
> returns the flags of the nth filter.

Can you split this up into factoring out the nth helper, and then
adding the new get?

For naming, perhaps "GET_FILTER_FLAGS" instead of "GET_FLAGS" since
there may be seccomp flags in the future, etc.

Is there any sane way to add the flags to the existing GET_FILTER?

-Kees

>
> Signed-off-by: Tycho Andersen <tycho@xxxxxxxxxx>
> CC: Kees Cook <keescook@xxxxxxxxxxxx>
> CC: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
> CC: Oleg Nesterov <oleg@xxxxxxxxxx>
> ---
> include/linux/seccomp.h | 7 +++++
> include/uapi/linux/ptrace.h | 1 +
> kernel/ptrace.c | 4 +++
> kernel/seccomp.c | 74 ++++++++++++++++++++++++++++++++++-----------
> 4 files changed, 68 insertions(+), 18 deletions(-)
>
> diff --git a/include/linux/seccomp.h b/include/linux/seccomp.h
> index c8bef436b61d..4713d62378e3 100644
> --- a/include/linux/seccomp.h
> +++ b/include/linux/seccomp.h
> @@ -94,11 +94,18 @@ static inline void get_seccomp_filter(struct task_struct *tsk)
> #if defined(CONFIG_SECCOMP_FILTER) && defined(CONFIG_CHECKPOINT_RESTORE)
> extern long seccomp_get_filter(struct task_struct *task,
> unsigned long filter_off, void __user *data);
> +extern long seccomp_get_flags(struct task_struct *task,
> + unsigned long filter_off);
> #else
> static inline long seccomp_get_filter(struct task_struct *task,
> unsigned long n, void __user *data)
> {
> return -EINVAL;
> }
> +static inline long seccomp_get_flags(struct task_struct *task,
> + unsigned long filter_off)
> +{
> + return -EINVAL;
> +}
> #endif /* CONFIG_SECCOMP_FILTER && CONFIG_CHECKPOINT_RESTORE */
> #endif /* _LINUX_SECCOMP_H */
> diff --git a/include/uapi/linux/ptrace.h b/include/uapi/linux/ptrace.h
> index fb8106509000..52903f0f6600 100644
> --- a/include/uapi/linux/ptrace.h
> +++ b/include/uapi/linux/ptrace.h
> @@ -65,6 +65,7 @@ struct ptrace_peeksiginfo_args {
> #define PTRACE_SETSIGMASK 0x420b
>
> #define PTRACE_SECCOMP_GET_FILTER 0x420c
> +#define PTRACE_SECCOMP_GET_FLAGS 0x420d
>
> /* Read signals from a shared (process wide) queue */
> #define PTRACE_PEEKSIGINFO_SHARED (1 << 0)
> diff --git a/kernel/ptrace.c b/kernel/ptrace.c
> index 60f356d91060..fa3d2b4d3bf0 100644
> --- a/kernel/ptrace.c
> +++ b/kernel/ptrace.c
> @@ -1094,6 +1094,10 @@ int ptrace_request(struct task_struct *child, long request,
> ret = seccomp_get_filter(child, addr, datavp);
> break;
>
> + case PTRACE_SECCOMP_GET_FLAGS:
> + ret = seccomp_get_flags(child, addr);
> + break;
> +
> default:
> break;
> }
> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
> index c24579dfa7a1..67768aaa7952 100644
> --- a/kernel/seccomp.c
> +++ b/kernel/seccomp.c
> @@ -968,24 +968,16 @@ long prctl_set_seccomp(unsigned long seccomp_mode, char __user *filter)
> }
>
> #if defined(CONFIG_SECCOMP_FILTER) && defined(CONFIG_CHECKPOINT_RESTORE)
> -long seccomp_get_filter(struct task_struct *task, unsigned long filter_off,
> - void __user *data)
> +static struct seccomp_filter *get_nth_filter(struct task_struct *task,
> + unsigned long filter_off)
> {
> struct seccomp_filter *filter;
> - struct sock_fprog_kern *fprog;
> - long ret;
> unsigned long count = 0;
>
> - if (!capable(CAP_SYS_ADMIN) ||
> - current->seccomp.mode != SECCOMP_MODE_DISABLED) {
> - return -EACCES;
> - }
> + WARN_ON_ONCE(!spin_is_locked(&task->sighand->siglock));
>
> - spin_lock_irq(&task->sighand->siglock);
> - if (task->seccomp.mode != SECCOMP_MODE_FILTER) {
> - ret = -EINVAL;
> - goto out;
> - }
> + if (task->seccomp.mode != SECCOMP_MODE_FILTER)
> + return ERR_PTR(-EINVAL);
>
> filter = task->seccomp.filter;
> while (filter) {
> @@ -993,10 +985,9 @@ long seccomp_get_filter(struct task_struct *task, unsigned long filter_off,
> count++;
> }
>
> - if (filter_off >= count) {
> - ret = -ENOENT;
> - goto out;
> - }
> + if (filter_off >= count)
> + return ERR_PTR(-ENOENT);
> +
> count -= filter_off;
>
> filter = task->seccomp.filter;
> @@ -1007,7 +998,28 @@ long seccomp_get_filter(struct task_struct *task, unsigned long filter_off,
>
> if (WARN_ON(count != 1 || !filter)) {
> /* The filter tree shouldn't shrink while we're using it. */
> - ret = -ENOENT;
> + return ERR_PTR(-ENOENT);
> + }
> +
> + return filter;
> +}
> +
> +long seccomp_get_filter(struct task_struct *task, unsigned long filter_off,
> + void __user *data)
> +{
> + struct seccomp_filter *filter;
> + struct sock_fprog_kern *fprog;
> + long ret;
> +
> + if (!capable(CAP_SYS_ADMIN) ||
> + current->seccomp.mode != SECCOMP_MODE_DISABLED) {
> + return -EACCES;
> + }
> +
> + spin_lock_irq(&task->sighand->siglock);
> + filter = get_nth_filter(task, filter_off);
> + if (IS_ERR(filter)) {
> + ret = PTR_ERR(filter);
> goto out;
> }
>
> @@ -1038,6 +1050,32 @@ long seccomp_get_filter(struct task_struct *task, unsigned long filter_off,
> spin_unlock_irq(&task->sighand->siglock);
> return ret;
> }
> +
> +long seccomp_get_flags(struct task_struct *task, unsigned long filter_off)
> +{
> + long flags = 0L;
> + struct seccomp_filter *filter;
> +
> + if (!capable(CAP_SYS_ADMIN) ||
> + current->seccomp.mode != SECCOMP_MODE_DISABLED) {
> + return -EACCES;
> + }
> +
> + spin_lock_irq(&task->sighand->siglock);
> + filter = get_nth_filter(task, filter_off);
> + if (IS_ERR(filter)) {
> + flags = PTR_ERR(filter);
> + goto out;
> + }
> +
> + if (filter->log)
> + flags |= SECCOMP_FILTER_FLAG_LOG;
> +
> +out:
> + spin_unlock_irq(&task->sighand->siglock);
> + return flags;
> +
> +}
> #endif
>
> #ifdef CONFIG_SYSCTL
> --
> 2.11.0
>



--
Kees Cook
Pixel Security