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SubjectRe: [PATCH v4 2/2] ptrace, seccomp: add support for retrieving seccomp metadata
On Tue, Nov 14, 2017 at 07:00:19PM -0700, Tycho Andersen 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_METADATA, similar to ..._GET_FILTER, which
> returns the metadata of the nth filter (right now, just the flags).
> Hopefully this will be future proof, and new per-filter metadata can be
> added to this struct.
>
> v3: * use GET_METADATA instead of GET_FLAGS
> v4: * resend
>
> Signed-off-by: Tycho Andersen <tycho@tycho.ws>
> CC: Kees Cook <keescook@chromium.org>
> CC: Andy Lutomirski <luto@amacapital.net>
> CC: Oleg Nesterov <oleg@redhat.com>
> ---
> include/linux/seccomp.h | 8 ++++++++
> include/uapi/linux/ptrace.h | 6 ++++++
> kernel/ptrace.c | 4 ++++
> kernel/seccomp.c | 34 ++++++++++++++++++++++++++++++++++
> 4 files changed, 52 insertions(+)
>
> diff --git a/include/linux/seccomp.h b/include/linux/seccomp.h
> index 10f25f7e4304..c723a5c4e3ff 100644
> --- a/include/linux/seccomp.h
> +++ b/include/linux/seccomp.h
> @@ -95,11 +95,19 @@ 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_metadata(struct task_struct *task,
> + unsigned long filter_off, void __user *data);
> #else
> static inline long seccomp_get_filter(struct task_struct *task,
> unsigned long n, void __user *data)
> {
> return -EINVAL;
> }
> +static inline long seccomp_get_metadata(struct task_struct *task,
> + unsigned long filter_off,
> + void __user *data)
> +{
> + 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 e3939e00980b..e46d82b91166 100644
> --- a/include/uapi/linux/ptrace.h
> +++ b/include/uapi/linux/ptrace.h
> @@ -66,6 +66,12 @@ struct ptrace_peeksiginfo_args {
> #define PTRACE_SETSIGMASK 0x420b
>
> #define PTRACE_SECCOMP_GET_FILTER 0x420c
> +#define PTRACE_SECCOMP_GET_METADATA 0x420d
> +
> +struct seccomp_metadata {
> + unsigned long filter_off; /* Input: which filter */
> + unsigned int flags; /* Output: filter's flags */
> +};
>
> /* 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 84b1367935e4..58291e9f3276 100644
> --- a/kernel/ptrace.c
> +++ b/kernel/ptrace.c
> @@ -1092,6 +1092,10 @@ int ptrace_request(struct task_struct *child, long request,
> ret = seccomp_get_filter(child, addr, datavp);
> break;
>
> + case PTRACE_SECCOMP_GET_METADATA:
> + ret = seccomp_get_metadata(child, addr, datavp);
> + break;
> +
> default:
> break;
> }
> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
> index bad457862ee0..7f1f2f3ea549 100644
> --- a/kernel/seccomp.c
> +++ b/kernel/seccomp.c
> @@ -1061,6 +1061,40 @@ long seccomp_get_filter(struct task_struct *task, unsigned long filter_off,
> __put_seccomp_filter(filter);
> return ret;
> }
> +
> +long seccomp_get_metadata(struct task_struct *task,
> + unsigned long size, void __user *data)
> +{
> + long ret;
> + struct seccomp_filter *filter;
> + struct seccomp_metadata kmd = {};
> +
> + if (!capable(CAP_SYS_ADMIN) ||
> + current->seccomp.mode != SECCOMP_MODE_DISABLED) {
> + return -EACCES;
> + }
> +

> + size = min_t(unsigned long, size, sizeof(kmd));
> +
> + if (copy_from_user(&kmd, data, size))
> + return -EFAULT;

This will work kinda funny if size is less than sizeof(kmd.filter_off).
And I see no reason for copying the whole structure when only filter_off
is needed.

> +
> + filter = get_nth_filter(task, kmd.filter_off);
> + if (IS_ERR(filter))
> + return PTR_ERR(filter);
> +
> + memset(&kmd, 0, sizeof(kmd));

Is rewriting the filter_off field to 0 intentional?

> + if (filter->log)
> + kmd.flags |= SECCOMP_FILTER_FLAG_LOG;
> +
> + ret = size;
> + if (copy_to_user(data, &kmd, size))
> + ret = -EFAULT;
> +
> + __put_seccomp_filter(filter);
> + return ret;
> +
> +}
> #endif
>
> #ifdef CONFIG_SYSCTL
> --
> 2.14.1
>

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