Re: [PATCH v7 1/6] seccomp: add a return code to trap to userspace

Kees Cook
2018-09-27T21:31:33Z

On Thu, Sep 27, 2018 at 8:11 AM, Tycho Andersen <tycho@tycho.ws> wrote:
> This patch introduces a means for syscalls matched in seccomp to notify
> some other task that a particular filter has been triggered.
>
> The motivation for this is primarily for use with containers. For example,
> if a container does an init_module(), we obviously don't want to load this
> untrusted code, which may be compiled for the wrong version of the kernel
> anyway. Instead, we could parse the module image, figure out which module
> the container is trying to load and load it on the host.
>
> As another example, containers cannot mknod(), since this checks
> capable(CAP_SYS_ADMIN). However, harmless devices like /dev/null or
> /dev/zero should be ok for containers to mknod, but we'd like to avoid hard
> coding some whitelist in the kernel. Another example is mount(), which has
> many security restrictions for good reason, but configuration or runtime
> knowledge could potentially be used to relax these restrictions.
>
> This patch adds functionality that is already possible via at least two
> other means that I know about, both of which involve ptrace(): first, one
> could ptrace attach, and then iterate through syscalls via PTRACE_SYSCALL.
> Unfortunately this is slow, so a faster version would be to install a
> filter that does SECCOMP_RET_TRACE, which triggers a PTRACE_EVENT_SECCOMP.
> Since ptrace allows only one tracer, if the container runtime is that
> tracer, users inside the container (or outside) trying to debug it will not
> be able to use ptrace, which is annoying. It also means that older
> distributions based on Upstart cannot boot inside containers using ptrace,
> since upstart itself uses ptrace to start services.
>
> The actual implementation of this is fairly small, although getting the
> synchronization right was/is slightly complex.
>
> Finally, it's worth noting that the classic seccomp TOCTOU of reading
> memory data from the task still applies here, but can be avoided with
> careful design of the userspace handler: if the userspace handler reads all
> of the task memory that is necessary before applying its security policy,
> the tracee's subsequent memory edits will not be read by the tracer.
>
> v2: * make id a u64; the idea here being that it will never overflow,
> because 64 is huge (one syscall every nanosecond => wrap every 584
> years) (Andy)
> * prevent nesting of user notifications: if someone is already attached
> the tree in one place, nobody else can attach to the tree (Andy)
> * notify the listener of signals the tracee receives as well (Andy)
> * implement poll
> v3: * lockdep fix (Oleg)
> * drop unnecessary WARN()s (Christian)
> * rearrange error returns to be more rpetty (Christian)
> * fix build in !CONFIG_SECCOMP_USER_NOTIFICATION case
> v4: * fix implementation of poll to use poll_wait() (Jann)
> * change listener's fd flags to be 0 (Jann)
> * hoist filter initialization out of ifdefs to its own function
> init_user_notification()
> * add some more testing around poll() and closing the listener while a
> syscall is in action
> * s/GET_LISTENER/NEW_LISTENER, since you can't _get_ a listener, but it
> creates a new one (Matthew)
> * correctly handle pid namespaces, add some testcases (Matthew)
> * use EINPROGRESS instead of EINVAL when a notification response is
> written twice (Matthew)
> * fix comment typo from older version (SEND vs READ) (Matthew)
> * whitespace and logic simplification (Tobin)
> * add some Documentation/ bits on userspace trapping
> v5: * fix documentation typos (Jann)
> * add signalled field to struct seccomp_notif (Jann)
> * switch to using ioctls instead of read()/write() for struct passing
> (Jann)
> * add an ioctl to ensure an id is still valid
> v6: * docs typo fixes, update docs for ioctl() change (Christian)
> v7: * switch struct seccomp_knotif's id member to a u64 (derp :)
> * use notify_lock in IS_ID_VALID query to avoid racing
> * s/signalled/signaled (Tyler)
> * fix docs to reflect that ids are not globally unique (Tyler)
> * add a test to check -ERESTARTSYS behavior (Tyler)
> * drop CONFIG_SECCOMP_USER_NOTIFICATION (Tyler)
> * reorder USER_NOTIF in seccomp return codes list (Tyler)
> * return size instead of sizeof(struct user_notif) (Tyler)
> * ENOENT instead of EINVAL when invalid id is passed (Tyler)
> * drop CONFIG_SECCOMP_USER_NOTIFICATION guards (Tyler)
> * s/IS_ID_VALID/ID_VALID and switch ioctl to be "well behaved" (Tyler)
> * add a new struct notification to minimize the additions to
> struct seccomp_filter, also pack the necessary additions a bit more
> cleverly (Tyler)
> * switch to keeping track of the task itself instead of the pid (we'll
> use this for implementing PUT_FD)

Patch-sending nit: can you put the versioning below the "---" line so
it isn't included in the final commit? (And I normally read these
backwards, so I'd expect v7 at the top, but that's not a big deal. I
mean... neither is the --- thing, but it makes "git am" easier for me
since I don't have to go edit the versioning out of the log.)

> 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>
> CC: Eric W. Biederman <ebiederm@xmission.com>
> CC: "Serge E. Hallyn" <serge@hallyn.com>
> CC: Christian Brauner <christian.brauner@ubuntu.com>
> CC: Tyler Hicks <tyhicks@canonical.com>
> CC: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>
> ---
> Documentation/ioctl/ioctl-number.txt | 1 +
> .../userspace-api/seccomp_filter.rst | 73 +++
> include/linux/seccomp.h | 7 +-
> include/uapi/linux/seccomp.h | 33 +-
> kernel/seccomp.c | 436 +++++++++++++++++-
> tools/testing/selftests/seccomp/seccomp_bpf.c | 413 ++++++++++++++++-
> 6 files changed, 954 insertions(+), 9 deletions(-)
>
> diff --git a/Documentation/ioctl/ioctl-number.txt b/Documentation/ioctl/ioctl-number.txt
> index 13a7c999c04a..31e9707f7e06 100644
> --- a/Documentation/ioctl/ioctl-number.txt
> +++ b/Documentation/ioctl/ioctl-number.txt
> @@ -345,4 +345,5 @@ Code Seq#(hex) Include File Comments
> <mailto:raph@8d.com>
> 0xF6 all LTTng Linux Trace Toolkit Next Generation
> <mailto:mathieu.desnoyers@efficios.com>
> +0xF7 00-1F uapi/linux/seccomp.h
> 0xFD all linux/dm-ioctl.h

I spent some time looking at this, and yes, it seems preferred to add
an entry here.

> diff --git a/include/linux/seccomp.h b/include/linux/seccomp.h
> index e5320f6c8654..017444b5efed 100644
> --- a/include/linux/seccomp.h
> +++ b/include/linux/seccomp.h
> @@ -4,9 +4,10 @@
>
> #include <uapi/linux/seccomp.h>
>
> -#define SECCOMP_FILTER_FLAG_MASK (SECCOMP_FILTER_FLAG_TSYNC | \
> - SECCOMP_FILTER_FLAG_LOG | \
> - SECCOMP_FILTER_FLAG_SPEC_ALLOW)
> +#define SECCOMP_FILTER_FLAG_MASK (SECCOMP_FILTER_FLAG_TSYNC | \
> + SECCOMP_FILTER_FLAG_LOG | \
> + SECCOMP_FILTER_FLAG_SPEC_ALLOW | \
> + SECCOMP_FILTER_FLAG_NEW_LISTENER)
>
> #ifdef CONFIG_SECCOMP
>
> diff --git a/include/uapi/linux/seccomp.h b/include/uapi/linux/seccomp.h
> index 9efc0e73d50b..d4ccb32fe089 100644
> --- a/include/uapi/linux/seccomp.h
> +++ b/include/uapi/linux/seccomp.h
> @@ -17,9 +17,10 @@
> #define SECCOMP_GET_ACTION_AVAIL 2
>
> /* Valid flags for SECCOMP_SET_MODE_FILTER */
> -#define SECCOMP_FILTER_FLAG_TSYNC (1UL << 0)
> -#define SECCOMP_FILTER_FLAG_LOG (1UL << 1)
> -#define SECCOMP_FILTER_FLAG_SPEC_ALLOW (1UL << 2)
> +#define SECCOMP_FILTER_FLAG_TSYNC (1UL << 0)
> +#define SECCOMP_FILTER_FLAG_LOG (1UL << 1)
> +#define SECCOMP_FILTER_FLAG_SPEC_ALLOW (1UL << 2)
> +#define SECCOMP_FILTER_FLAG_NEW_LISTENER (1UL << 3)

Since these are all getting indentation updates, can you switch them
to BIT(0), BIT(1), etc?

> /*
> * All BPF programs must return a 32-bit value.
> @@ -35,6 +36,7 @@
> #define SECCOMP_RET_KILL SECCOMP_RET_KILL_THREAD
> #define SECCOMP_RET_TRAP 0x00030000U /* disallow and force a SIGSYS */
> #define SECCOMP_RET_ERRNO 0x00050000U /* returns an errno */
> +#define SECCOMP_RET_USER_NOTIF 0x7fc00000U /* notifies userspace */
> #define SECCOMP_RET_TRACE 0x7ff00000U /* pass to a tracer or disallow */
> #define SECCOMP_RET_LOG 0x7ffc0000U /* allow after logging */
> #define SECCOMP_RET_ALLOW 0x7fff0000U /* allow */
> @@ -60,4 +62,29 @@ struct seccomp_data {
> __u64 args[6];
> };
>
> +struct seccomp_notif {
> + __u16 len;
> + __u64 id;
> + __u32 pid;
> + __u8 signaled;
> + struct seccomp_data data;
> +};
> +
> +struct seccomp_notif_resp {
> + __u16 len;
> + __u64 id;
> + __s32 error;
> + __s64 val;
> +};

So, len has to come first, for versioning. However, since it's ahead
of a u64, this leaves a struct padding hole. pahole output:

struct seccomp_notif {
__u16 len; /* 0 2 */

/* XXX 6 bytes hole, try to pack */

__u64 id; /* 8 8 */
__u32 pid; /* 16 4 */
__u8 signaled; /* 20 1 */

/* XXX 3 bytes hole, try to pack */

struct seccomp_data data; /* 24 64 */
/* --- cacheline 1 boundary (64 bytes) was 24 bytes ago --- */

/* size: 88, cachelines: 2, members: 5 */
/* sum members: 79, holes: 2, sum holes: 9 */
/* last cacheline: 24 bytes */
};
struct seccomp_notif_resp {
__u16 len; /* 0 2 */

/* XXX 6 bytes hole, try to pack */

__u64 id; /* 8 8 */
__s32 error; /* 16 4 */

/* XXX 4 bytes hole, try to pack */

__s64 val; /* 24 8 */

/* size: 32, cachelines: 1, members: 4 */
/* sum members: 22, holes: 2, sum holes: 10 */
/* last cacheline: 32 bytes */
};

How about making len u32, and moving pid and error above "id"? This
leaves a hole after signaled, so changing "len" won't be sufficient
for versioning here. Perhaps move it after data?

> +
> +#define SECCOMP_IOC_MAGIC 0xF7

Was there any specific reason for picking this value? There are lots
of fun ASCII code left like '!' or '*'. :)

> +
> +/* Flags for seccomp notification fd ioctl. */
> +#define SECCOMP_NOTIF_RECV _IOWR(SECCOMP_IOC_MAGIC, 0, \
> + struct seccomp_notif)
> +#define SECCOMP_NOTIF_SEND _IOWR(SECCOMP_IOC_MAGIC, 1, \
> + struct seccomp_notif_resp)
> +#define SECCOMP_NOTIF_ID_VALID _IOR(SECCOMP_IOC_MAGIC, 2, \
> + __u64)

To match other UAPI ioctl, can these have a prefix of "SECCOMP_IOCTOL_..."?

It may also be useful to match how other uapis do this, like for DRM:

#define DRM_IOCTL_BASE 'd'
#define DRM_IO(nr) _IO(DRM_IOCTL_BASE,nr)
#define DRM_IOR(nr,type) _IOR(DRM_IOCTL_BASE,nr,type)
#define DRM_IOW(nr,type) _IOW(DRM_IOCTL_BASE,nr,type)
#define DRM_IOWR(nr,type) _IOWR(DRM_IOCTL_BASE,nr,type)

#define DRM_IOCTL_VERSION DRM_IOWR(0x00, struct drm_version)
#define DRM_IOCTL_GET_UNIQUE DRM_IOWR(0x01, struct drm_unique)
#define DRM_IOCTL_GET_MAGIC DRM_IOR( 0x02, struct drm_auth)
...

> +
> #endif /* _UAPI_LINUX_SECCOMP_H */
> diff --git a/kernel/seccomp.c b/kernel/seccomp.c
> index fd023ac24e10..fa6fe9756c80 100644
> --- a/kernel/seccomp.c
> +++ b/kernel/seccomp.c
> @@ -33,12 +33,78 @@
> #endif
>
> #ifdef CONFIG_SECCOMP_FILTER
> +#include <linux/file.h>
> #include <linux/filter.h>
> #include <linux/pid.h>
> #include <linux/ptrace.h>
> #include <linux/security.h>
> #include <linux/tracehook.h>
> #include <linux/uaccess.h>
> +#include <linux/anon_inodes.h>
> +
> +enum notify_state {
> + SECCOMP_NOTIFY_INIT,
> + SECCOMP_NOTIFY_SENT,
> + SECCOMP_NOTIFY_REPLIED,
> +};
> +
> +struct seccomp_knotif {
> + /* The struct pid of the task whose filter triggered the notification */
> + struct task_struct *task;
> +
> + /* The "cookie" for this request; this is unique for this filter. */
> + u64 id;
> +
> + /* Whether or not this task has been given an interruptible signal. */
> + bool signaled;
> +
> + /*
> + * The seccomp data. This pointer is valid the entire time this
> + * notification is active, since it comes from __seccomp_filter which
> + * eclipses the entire lifecycle here.
> + */
> + const struct seccomp_data *data;
> +
> + /*
> + * Notification states. When SECCOMP_RET_USER_NOTIF is returned, a
> + * struct seccomp_knotif is created and starts out in INIT. Once the
> + * handler reads the notification off of an FD, it transitions to SENT.
> + * If a signal is received the state transitions back to INIT and
> + * another message is sent. When the userspace handler replies, state
> + * transitions to REPLIED.
> + */
> + enum notify_state state;
> +
> + /* The return values, only valid when in SECCOMP_NOTIFY_REPLIED */
> + int error;
> + long val;
> +
> + /* Signals when this has entered SECCOMP_NOTIFY_REPLIED */
> + struct completion ready;
> +
> + struct list_head list;
> +};
> +
> +/**
> + * struct notification - container for seccomp userspace notifications. Since
> + * most seccomp filters will not have notification listeners attached and this
> + * structure is fairly large, we store the notification-specific stuff in a
> + * separate structure.
> + *
> + * @request: A semaphore that users of this notification can wait on for
> + * changes. Actual reads and writes are still controlled with
> + * filter->notify_lock.
> + * @notify_lock: A lock for all notification-related accesses.
> + * @next_id: The id of the next request.
> + * @notifications: A list of struct seccomp_knotif elements.
> + * @wqh: A wait queue for poll.
> + */
> +struct notification {
> + struct semaphore request;
> + u64 next_id;
> + struct list_head notifications;
> + wait_queue_head_t wqh;
> +};
>
> /**
> * struct seccomp_filter - container for seccomp BPF programs
> @@ -66,6 +132,8 @@ struct seccomp_filter {
> bool log;
> struct seccomp_filter *prev;
> struct bpf_prog *prog;
> + struct notification *notif;
> + struct mutex notify_lock;
> };
>
> /* Limit any path through the tree to 256KB worth of instructions. */
> @@ -392,6 +460,7 @@ static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog)
> if (!sfilter)
> return ERR_PTR(-ENOMEM);
>
> + mutex_init(&sfilter->notify_lock);
> ret = bpf_prog_create_from_user(&sfilter->prog, fprog,
> seccomp_check_filter, save_orig);
> if (ret < 0) {
> @@ -556,11 +625,13 @@ static void seccomp_send_sigsys(int syscall, int reason)
> #define SECCOMP_LOG_TRACE (1 << 4)
> #define SECCOMP_LOG_LOG (1 << 5)
> #define SECCOMP_LOG_ALLOW (1 << 6)
> +#define SECCOMP_LOG_USER_NOTIF (1 << 7)
>
> static u32 seccomp_actions_logged = SECCOMP_LOG_KILL_PROCESS |
> SECCOMP_LOG_KILL_THREAD |
> SECCOMP_LOG_TRAP |
> SECCOMP_LOG_ERRNO |
> + SECCOMP_LOG_USER_NOTIF |
> SECCOMP_LOG_TRACE |
> SECCOMP_LOG_LOG;
>
> @@ -581,6 +652,9 @@ static inline void seccomp_log(unsigned long syscall, long signr, u32 action,
> case SECCOMP_RET_TRACE:
> log = requested && seccomp_actions_logged & SECCOMP_LOG_TRACE;
> break;
> + case SECCOMP_RET_USER_NOTIF:
> + log = requested && seccomp_actions_logged & SECCOMP_LOG_USER_NOTIF;
> + break;
> case SECCOMP_RET_LOG:
> log = seccomp_actions_logged & SECCOMP_LOG_LOG;
> break;
> @@ -652,6 +726,73 @@ void secure_computing_strict(int this_syscall)
> #else
>
> #ifdef CONFIG_SECCOMP_FILTER
> +static u64 seccomp_next_notify_id(struct seccomp_filter *filter)
> +{
> + /* Note: overflow is ok here, the id just needs to be unique */

Maybe just clarify in the comment: unique to the filter.

> + return filter->notif->next_id++;

Also, it might be useful to add for both documentation and lockdep:

lockdep_assert_held(filter->notif->notify_lock);

into this function?

> +}
> +
> +static void seccomp_do_user_notification(int this_syscall,
> + struct seccomp_filter *match,
> + const struct seccomp_data *sd)
> +{
> + int err;
> + long ret = 0;
> + struct seccomp_knotif n = {};
> +
> + mutex_lock(&match->notify_lock);
> + err = -ENOSYS;
> + if (!match->notif)
> + goto out;
> +
> + n.task = current;
> + n.state = SECCOMP_NOTIFY_INIT;
> + n.data = sd;
> + n.id = seccomp_next_notify_id(match);
> + init_completion(&n.ready);
> +
> + list_add(&n.list, &match->notif->notifications);
> + wake_up_poll(&match->notif->wqh, EPOLLIN | EPOLLRDNORM);
> +
> + mutex_unlock(&match->notify_lock);
> + up(&match->notif->request);
> +

Maybe add a big comment here saying this is where we're waiting for a reply?

> + err = wait_for_completion_interruptible(&n.ready);
> + mutex_lock(&match->notify_lock);
> +
> + /*
> + * Here it's possible we got a signal and then had to wait on the mutex
> + * while the reply was sent, so let's be sure there wasn't a response
> + * in the meantime.
> + */
> + if (err < 0 && n.state != SECCOMP_NOTIFY_REPLIED) {
> + /*
> + * We got a signal. Let's tell userspace about it (potentially
> + * again, if we had already notified them about the first one).
> + */
> + n.signaled = true;
> + if (n.state == SECCOMP_NOTIFY_SENT) {
> + n.state = SECCOMP_NOTIFY_INIT;
> + up(&match->notif->request);
> + }
> + mutex_unlock(&match->notify_lock);
> + err = wait_for_completion_killable(&n.ready);
> + mutex_lock(&match->notify_lock);
> + if (err < 0)
> + goto remove_list;
> + }
> +
> + ret = n.val;
> + err = n.error;
> +
> +remove_list:
> + list_del(&n.list);
> +out:
> + mutex_unlock(&match->notify_lock);
> + syscall_set_return_value(current, task_pt_regs(current),
> + err, ret);
> +}
> +
> static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
> const bool recheck_after_trace)
> {
> @@ -728,6 +869,9 @@ static int __seccomp_filter(int this_syscall, const struct seccomp_data *sd,
>
> return 0;
>
> + case SECCOMP_RET_USER_NOTIF:
> + seccomp_do_user_notification(this_syscall, match, sd);
> + goto skip;

Nit: please add a blank line here (to match the other cases).

> case SECCOMP_RET_LOG:
> seccomp_log(this_syscall, 0, action, true);
> return 0;
> @@ -834,6 +978,9 @@ static long seccomp_set_mode_strict(void)
> }
>
> #ifdef CONFIG_SECCOMP_FILTER
> +static struct file *init_listener(struct task_struct *,
> + struct seccomp_filter *);

Why is the forward declaration needed instead of just moving the
function here? I didn't see anything in it that looked like it
couldn't move.

> +
> /**
> * seccomp_set_mode_filter: internal function for setting seccomp filter
> * @flags: flags to change filter behavior
> @@ -853,6 +1000,8 @@ static long seccomp_set_mode_filter(unsigned int flags,
> const unsigned long seccomp_mode = SECCOMP_MODE_FILTER;
> struct seccomp_filter *prepared = NULL;
> long ret = -EINVAL;
> + int listener = 0;

Nit: "invalid fd" should be -1, not 0.

> + struct file *listener_f = NULL;
>
> /* Validate flags. */
> if (flags & ~SECCOMP_FILTER_FLAG_MASK)
> @@ -863,13 +1012,28 @@ static long seccomp_set_mode_filter(unsigned int flags,
> if (IS_ERR(prepared))
> return PTR_ERR(prepared);
>
> + if (flags & SECCOMP_FILTER_FLAG_NEW_LISTENER) {
> + listener = get_unused_fd_flags(0);

As with the other place pointed out by Jann, this should maybe be O_CLOEXEC too?

> + if (listener < 0) {
> + ret = listener;
> + goto out_free;
> + }
> +
> + listener_f = init_listener(current, prepared);
> + if (IS_ERR(listener_f)) {
> + put_unused_fd(listener);
> + ret = PTR_ERR(listener_f);
> + goto out_free;
> + }
> + }
> +
> /*
> * Make sure we cannot change seccomp or nnp state via TSYNC
> * while another thread is in the middle of calling exec.
> */
> if (flags & SECCOMP_FILTER_FLAG_TSYNC &&
> mutex_lock_killable(&current->signal->cred_guard_mutex))
> - goto out_free;
> + goto out_put_fd;
>
> spin_lock_irq(&current->sighand->siglock);
>
> @@ -887,6 +1051,16 @@ static long seccomp_set_mode_filter(unsigned int flags,
> spin_unlock_irq(&current->sighand->siglock);
> if (flags & SECCOMP_FILTER_FLAG_TSYNC)
> mutex_unlock(&current->signal->cred_guard_mutex);
> +out_put_fd:
> + if (flags & SECCOMP_FILTER_FLAG_NEW_LISTENER) {
> + if (ret < 0) {
> + fput(listener_f);
> + put_unused_fd(listener);
> + } else {
> + fd_install(listener, listener_f);
> + ret = listener;
> + }
> + }

Can you update the kern-docs for seccomp_set_mode_filter(), since we
can now return positive values?

* Returns 0 on success or -EINVAL on failure.

(this shoudln't say only -EINVAL, I realize too)

I have to say, I'm vaguely nervous about changing the semantics here
for passing back the fd as the return code from the seccomp() syscall.
Alternatives seem less appealing, though: changing the meaning of the
uargs parameter when SECCOMP_FILTER_FLAG_NEW_LISTENER is set, for
example. Hmm.

> out_free:
> seccomp_filter_free(prepared);
> return ret;
> @@ -911,6 +1085,7 @@ static long seccomp_get_action_avail(const char __user *uaction)
> case SECCOMP_RET_KILL_THREAD:
> case SECCOMP_RET_TRAP:
> case SECCOMP_RET_ERRNO:
> + case SECCOMP_RET_USER_NOTIF:
> case SECCOMP_RET_TRACE:
> case SECCOMP_RET_LOG:
> case SECCOMP_RET_ALLOW:
> @@ -1111,6 +1286,7 @@ long seccomp_get_metadata(struct task_struct *task,
> #define SECCOMP_RET_KILL_THREAD_NAME "kill_thread"
> #define SECCOMP_RET_TRAP_NAME "trap"
> #define SECCOMP_RET_ERRNO_NAME "errno"
> +#define SECCOMP_RET_USER_NOTIF_NAME "user_notif"
> #define SECCOMP_RET_TRACE_NAME "trace"
> #define SECCOMP_RET_LOG_NAME "log"
> #define SECCOMP_RET_ALLOW_NAME "allow"
> @@ -1120,6 +1296,7 @@ static const char seccomp_actions_avail[] =
> SECCOMP_RET_KILL_THREAD_NAME " "
> SECCOMP_RET_TRAP_NAME " "
> SECCOMP_RET_ERRNO_NAME " "
> + SECCOMP_RET_USER_NOTIF_NAME " "
> SECCOMP_RET_TRACE_NAME " "
> SECCOMP_RET_LOG_NAME " "
> SECCOMP_RET_ALLOW_NAME;
> @@ -1134,6 +1311,7 @@ static const struct seccomp_log_name seccomp_log_names[] = {
> { SECCOMP_LOG_KILL_THREAD, SECCOMP_RET_KILL_THREAD_NAME },
> { SECCOMP_LOG_TRAP, SECCOMP_RET_TRAP_NAME },
> { SECCOMP_LOG_ERRNO, SECCOMP_RET_ERRNO_NAME },
> + { SECCOMP_LOG_USER_NOTIF, SECCOMP_RET_USER_NOTIF_NAME },
> { SECCOMP_LOG_TRACE, SECCOMP_RET_TRACE_NAME },
> { SECCOMP_LOG_LOG, SECCOMP_RET_LOG_NAME },
> { SECCOMP_LOG_ALLOW, SECCOMP_RET_ALLOW_NAME },
> @@ -1342,3 +1520,259 @@ static int __init seccomp_sysctl_init(void)
> device_initcall(seccomp_sysctl_init)
>
> #endif /* CONFIG_SYSCTL */
> +
> +#ifdef CONFIG_SECCOMP_FILTER
> +static int seccomp_notify_release(struct inode *inode, struct file *file)
> +{
> + struct seccomp_filter *filter = file->private_data;
> + struct seccomp_knotif *knotif;
> +
> + mutex_lock(&filter->notify_lock);
> +
> + /*
> + * If this file is being closed because e.g. the task who owned it
> + * died, let's wake everyone up who was waiting on us.
> + */
> + list_for_each_entry(knotif, &filter->notif->notifications, list) {
> + if (knotif->state == SECCOMP_NOTIFY_REPLIED)
> + continue;
> +
> + knotif->state = SECCOMP_NOTIFY_REPLIED;
> + knotif->error = -ENOSYS;
> + knotif->val = 0;
> +
> + complete(&knotif->ready);
> + }
> +
> + wake_up_all(&filter->notif->wqh);
> + kfree(filter->notif);
> + filter->notif = NULL;
> + mutex_unlock(&filter->notify_lock);

It looks like that means nothing waiting on knotif->ready can access
filter->notif without rechecking it, yes?

e.g. in seccomp_do_user_notification() I see:

up(&match->notif->request);

I *think* this isn't reachable due to the test for n.state !=
SECCOMP_NOTIFY_REPLIED, though. Perhaps, just for sanity and because
it's not fast-path, we could add a WARN_ON() while checking for
unreplied signal death?

n.signaled = true;
if (n.state == SECCOMP_NOTIFY_SENT) {
n.state = SECCOMP_NOTIFY_INIT;
if (!WARN_ON(match->notif))
up(&match->notif->request);
}
mutex_unlock(&match->notify_lock);

> + __put_seccomp_filter(filter);
> + return 0;
> +}
> +
> +static long seccomp_notify_recv(struct seccomp_filter *filter,
> + unsigned long arg)
> +{
> + struct seccomp_knotif *knotif = NULL, *cur;
> + struct seccomp_notif unotif = {};
> + ssize_t ret;
> + u16 size;
> + void __user *buf = (void __user *)arg;

I'd prefer this casting happen in seccomp_notify_ioctl(). This keeps
anything from accidentally using "arg" directly here.

> +
> + if (copy_from_user(&size, buf, sizeof(size)))
> + return -EFAULT;
> +
> + ret = down_interruptible(&filter->notif->request);
> + if (ret < 0)
> + return ret;
> +
> + mutex_lock(&filter->notify_lock);
> + list_for_each_entry(cur, &filter->notif->notifications, list) {
> + if (cur->state == SECCOMP_NOTIFY_INIT) {
> + knotif = cur;
> + break;
> + }
> + }
> +
> + /*
> + * If we didn't find a notification, it could be that the task was
> + * interrupted between the time we were woken and when we were able to
> + * acquire the rw lock.
> + */
> + if (!knotif) {
> + ret = -ENOENT;
> + goto out;
> + }
> +
> + size = min_t(size_t, size, sizeof(unotif));
> +

It is possible (though unlikely given the type widths involved here)
for unotif = {} to not initialize padding, so I would recommend an
explicit memset(&unotif, 0, sizeof(unotif)) here.

> + unotif.len = size;
> + unotif.id = knotif->id;
> + unotif.pid = task_pid_vnr(knotif->task);
> + unotif.signaled = knotif->signaled;
> + unotif.data = *(knotif->data);
> +
> + if (copy_to_user(buf, &unotif, size)) {
> + ret = -EFAULT;
> + goto out;
> + }
> +
> + ret = size;
> + knotif->state = SECCOMP_NOTIFY_SENT;
> + wake_up_poll(&filter->notif->wqh, EPOLLOUT | EPOLLWRNORM);
> +
> +
> +out:
> + mutex_unlock(&filter->notify_lock);

Is there some way to rearrange the locking here to avoid holding the
mutex while doing copy_to_user() (which userspace could block with
userfaultfd, and then stall all the other notifications for this
filter)?

> + return ret;
> +}
> +
> +static long seccomp_notify_send(struct seccomp_filter *filter,
> + unsigned long arg)
> +{
> + struct seccomp_notif_resp resp = {};
> + struct seccomp_knotif *knotif = NULL;
> + long ret;
> + u16 size;
> + void __user *buf = (void __user *)arg;

Same cast note as above.

> +
> + if (copy_from_user(&size, buf, sizeof(size)))
> + return -EFAULT;
> + size = min_t(size_t, size, sizeof(resp));
> + if (copy_from_user(&resp, buf, size))
> + return -EFAULT;

For sanity checking on a double-read from userspace, please add:

if (resp.len != size)
return -EINVAL;

> +
> + ret = mutex_lock_interruptible(&filter->notify_lock);
> + if (ret < 0)
> + return ret;
> +
> + list_for_each_entry(knotif, &filter->notif->notifications, list) {
> + if (knotif->id == resp.id)
> + break;
> + }
> +
> + if (!knotif || knotif->id != resp.id) {
> + ret = -ENOENT;
> + goto out;
> + }
> +
> + /* Allow exactly one reply. */
> + if (knotif->state != SECCOMP_NOTIFY_SENT) {
> + ret = -EINPROGRESS;
> + goto out;
> + }
> +
> + ret = size;
> + knotif->state = SECCOMP_NOTIFY_REPLIED;
> + knotif->error = resp.error;
> + knotif->val = resp.val;
> + complete(&knotif->ready);
> +out:
> + mutex_unlock(&filter->notify_lock);
> + return ret;
> +}
> +
> +static long seccomp_notify_id_valid(struct seccomp_filter *filter,
> + unsigned long arg)
> +{
> + struct seccomp_knotif *knotif = NULL;
> + void __user *buf = (void __user *)arg;
> + u64 id;
> + long ret;
> +
> + if (copy_from_user(&id, buf, sizeof(id)))
> + return -EFAULT;
> +
> + ret = mutex_lock_interruptible(&filter->notify_lock);
> + if (ret < 0)
> + return ret;
> +
> + ret = -1;

Isn't this EPERM? Shouldn't it be -ENOENT?

> + list_for_each_entry(knotif, &filter->notif->notifications, list) {
> + if (knotif->id == id) {
> + ret = 0;
> + goto out;
> + }
> + }
> +
> +out:
> + mutex_unlock(&filter->notify_lock);
> + return ret;
> +}
> +
> +static long seccomp_notify_ioctl(struct file *file, unsigned int cmd,
> + unsigned long arg)
> +{
> + struct seccomp_filter *filter = file->private_data;
> +
> + switch (cmd) {
> + case SECCOMP_NOTIF_RECV:
> + return seccomp_notify_recv(filter, arg);
> + case SECCOMP_NOTIF_SEND:
> + return seccomp_notify_send(filter, arg);
> + case SECCOMP_NOTIF_ID_VALID:
> + return seccomp_notify_id_valid(filter, arg);
> + default:
> + return -EINVAL;
> + }
> +}
> +
> +static __poll_t seccomp_notify_poll(struct file *file,
> + struct poll_table_struct *poll_tab)
> +{
> + struct seccomp_filter *filter = file->private_data;
> + __poll_t ret = 0;
> + struct seccomp_knotif *cur;
> +
> + poll_wait(file, &filter->notif->wqh, poll_tab);
> +
> + ret = mutex_lock_interruptible(&filter->notify_lock);
> + if (ret < 0)
> + return ret;
> +
> + list_for_each_entry(cur, &filter->notif->notifications, list) {
> + if (cur->state == SECCOMP_NOTIFY_INIT)
> + ret |= EPOLLIN | EPOLLRDNORM;
> + if (cur->state == SECCOMP_NOTIFY_SENT)
> + ret |= EPOLLOUT | EPOLLWRNORM;
> + if (ret & EPOLLIN && ret & EPOLLOUT)

My eyes! :) Can you wrap the bit operations in parens here?

> + break;
> + }

Should POLLERR be handled here too? I don't quite see the conditions
that might be exposed? All the processes die for the filter, which
does what here?

> +
> + mutex_unlock(&filter->notify_lock);
> +
> + return ret;
> +}
> +
> +static const struct file_operations seccomp_notify_ops = {
> + .poll = seccomp_notify_poll,
> + .release = seccomp_notify_release,
> + .unlocked_ioctl = seccomp_notify_ioctl,
> +};
> +
> +static struct file *init_listener(struct task_struct *task,
> + struct seccomp_filter *filter)
> +{
> + struct file *ret = ERR_PTR(-EBUSY);
> + struct seccomp_filter *cur, *last_locked = NULL;
> + int filter_nesting = 0;
> +
> + for (cur = task->seccomp.filter; cur; cur = cur->prev) {
> + mutex_lock_nested(&cur->notify_lock, filter_nesting);
> + filter_nesting++;
> + last_locked = cur;
> + if (cur->notif)
> + goto out;
> + }
> +
> + ret = ERR_PTR(-ENOMEM);
> + filter->notif = kzalloc(sizeof(*(filter->notif)), GFP_KERNEL);
> + if (!filter->notif)
> + goto out;
> +
> + sema_init(&filter->notif->request, 0);
> + INIT_LIST_HEAD(&filter->notif->notifications);
> + filter->notif->next_id = get_random_u64();
> + init_waitqueue_head(&filter->notif->wqh);
> +
> + ret = anon_inode_getfile("seccomp notify", &seccomp_notify_ops,
> + filter, O_RDWR);
> + if (IS_ERR(ret))
> + goto out;
> +
> +
> + /* The file has a reference to it now */
> + __get_seccomp_filter(filter);
> +
> +out:
> + for (cur = task->seccomp.filter; cur; cur = cur->prev) {
> + mutex_unlock(&cur->notify_lock);
> + if (cur == last_locked)
> + break;
> + }
> +
> + return ret;
> +}
> +#endif
> diff --git a/tools/testing/selftests/seccomp/seccomp_bpf.c b/tools/testing/selftests/seccomp/seccomp_bpf.c
> index e1473234968d..5f4b836a6792 100644
> --- a/tools/testing/selftests/seccomp/seccomp_bpf.c
> +++ b/tools/testing/selftests/seccomp/seccomp_bpf.c
> @@ -5,6 +5,7 @@
> * Test code for seccomp bpf.
> */
>
> +#define _GNU_SOURCE
> #include <sys/types.h>
>
> /*
> @@ -40,10 +41,12 @@
> #include <sys/fcntl.h>
> #include <sys/mman.h>
> #include <sys/times.h>
> +#include <sys/socket.h>
> +#include <sys/ioctl.h>
>
> -#define _GNU_SOURCE
> #include <unistd.h>
> #include <sys/syscall.h>
> +#include <poll.h>
>
> #include "../kselftest_harness.h"
>
> @@ -154,6 +157,34 @@ struct seccomp_metadata {
> };
> #endif
>
> +#ifndef SECCOMP_FILTER_FLAG_NEW_LISTENER
> +#define SECCOMP_FILTER_FLAG_NEW_LISTENER (1UL << 3)
> +
> +#define SECCOMP_RET_USER_NOTIF 0x7fc00000U
> +
> +#define SECCOMP_IOC_MAGIC 0xF7
> +#define SECCOMP_NOTIF_RECV _IOWR(SECCOMP_IOC_MAGIC, 0, \
> + struct seccomp_notif)
> +#define SECCOMP_NOTIF_SEND _IOWR(SECCOMP_IOC_MAGIC, 1, \
> + struct seccomp_notif_resp)
> +#define SECCOMP_NOTIF_ID_VALID _IOR(SECCOMP_IOC_MAGIC, 2, \
> + __u64)
> +struct seccomp_notif {
> + __u16 len;
> + __u64 id;
> + __u32 pid;
> + __u8 signaled;
> + struct seccomp_data data;
> +};
> +
> +struct seccomp_notif_resp {
> + __u16 len;
> + __u64 id;
> + __s32 error;
> + __s64 val;
> +};
> +#endif
> +
> #ifndef seccomp
> int seccomp(unsigned int op, unsigned int flags, void *args)
> {
> @@ -2077,7 +2108,8 @@ TEST(detect_seccomp_filter_flags)
> {
> unsigned int flags[] = { SECCOMP_FILTER_FLAG_TSYNC,
> SECCOMP_FILTER_FLAG_LOG,
> - SECCOMP_FILTER_FLAG_SPEC_ALLOW };
> + SECCOMP_FILTER_FLAG_SPEC_ALLOW,
> + SECCOMP_FILTER_FLAG_NEW_LISTENER };
> unsigned int flag, all_flags;
> int i;
> long ret;
> @@ -2933,6 +2965,383 @@ TEST(get_metadata)
> ASSERT_EQ(0, kill(pid, SIGKILL));
> }
>
> +static int user_trap_syscall(int nr, unsigned int flags)
> +{
> + struct sock_filter filter[] = {
> + BPF_STMT(BPF_LD+BPF_W+BPF_ABS,
> + offsetof(struct seccomp_data, nr)),
> + BPF_JUMP(BPF_JMP+BPF_JEQ+BPF_K, nr, 0, 1),
> + BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_USER_NOTIF),
> + BPF_STMT(BPF_RET+BPF_K, SECCOMP_RET_ALLOW),
> + };
> +
> + struct sock_fprog prog = {
> + .len = (unsigned short)ARRAY_SIZE(filter),
> + .filter = filter,
> + };
> +
> + return seccomp(SECCOMP_SET_MODE_FILTER, flags, &prog);
> +}
> +
> +static int read_notif(int listener, struct seccomp_notif *req)
> +{
> + int ret;
> +
> + do {
> + errno = 0;
> + req->len = sizeof(*req);
> + ret = ioctl(listener, SECCOMP_NOTIF_RECV, req);
> + } while (ret == -1 && errno == ENOENT);
> + return ret;
> +}
> +
> +static void signal_handler(int signal)
> +{
> +}
> +
> +#define USER_NOTIF_MAGIC 116983961184613L
> +TEST(get_user_notification_syscall)
> +{
> + pid_t pid;
> + long ret;
> + int status, listener;
> + struct seccomp_notif req = {};
> + struct seccomp_notif_resp resp = {};
> + struct pollfd pollfd;
> +
> + struct sock_filter filter[] = {
> + BPF_STMT(BPF_RET|BPF_K, SECCOMP_RET_ALLOW),
> + };
> + struct sock_fprog prog = {
> + .len = (unsigned short)ARRAY_SIZE(filter),
> + .filter = filter,
> + };
> +
> + pid = fork();
> + ASSERT_GE(pid, 0);
> +
> + /* Check that we get -ENOSYS with no listener attached */
> + if (pid == 0) {
> + if (user_trap_syscall(__NR_getpid, 0) < 0)
> + exit(1);
> + ret = syscall(__NR_getpid);
> + exit(ret >= 0 || errno != ENOSYS);
> + }
> +
> + EXPECT_EQ(waitpid(pid, &status, 0), pid);
> + EXPECT_EQ(true, WIFEXITED(status));
> + EXPECT_EQ(0, WEXITSTATUS(status));
> +
> + /* Add some no-op filters so that we (don't) trigger lockdep. */
> + EXPECT_EQ(seccomp(SECCOMP_SET_MODE_FILTER, 0, &prog), 0);
> + EXPECT_EQ(seccomp(SECCOMP_SET_MODE_FILTER, 0, &prog), 0);
> + EXPECT_EQ(seccomp(SECCOMP_SET_MODE_FILTER, 0, &prog), 0);
> + EXPECT_EQ(seccomp(SECCOMP_SET_MODE_FILTER, 0, &prog), 0);
> +
> + /* Check that the basic notification machinery works */
> + listener = user_trap_syscall(__NR_getpid,
> + SECCOMP_FILTER_FLAG_NEW_LISTENER);
> + EXPECT_GE(listener, 0);
> +
> + /* Installing a second listener in the chain should EBUSY */
> + EXPECT_EQ(user_trap_syscall(__NR_getpid,
> + SECCOMP_FILTER_FLAG_NEW_LISTENER),
> + -1);
> + EXPECT_EQ(errno, EBUSY);
> +
> + pid = fork();
> + ASSERT_GE(pid, 0);
> +
> + if (pid == 0) {
> + ret = syscall(__NR_getpid);
> + exit(ret != USER_NOTIF_MAGIC);
> + }
> +
> + pollfd.fd = listener;
> + pollfd.events = POLLIN | POLLOUT;
> +
> + EXPECT_GT(poll(&pollfd, 1, -1), 0);
> + EXPECT_EQ(pollfd.revents, POLLIN);
> +
> + req.len = sizeof(req);
> + EXPECT_EQ(ioctl(listener, SECCOMP_NOTIF_RECV, &req), sizeof(req));
> +
> + pollfd.fd = listener;
> + pollfd.events = POLLIN | POLLOUT;
> +
> + EXPECT_GT(poll(&pollfd, 1, -1), 0);
> + EXPECT_EQ(pollfd.revents, POLLOUT);
> +
> + EXPECT_EQ(req.data.nr, __NR_getpid);
> +
> + resp.len = sizeof(resp);
> + resp.id = req.id;
> + resp.error = 0;
> + resp.val = USER_NOTIF_MAGIC;
> +
> + EXPECT_EQ(ioctl(listener, SECCOMP_NOTIF_SEND, &resp), sizeof(resp));
> +
> + EXPECT_EQ(waitpid(pid, &status, 0), pid);
> + EXPECT_EQ(true, WIFEXITED(status));
> + EXPECT_EQ(0, WEXITSTATUS(status));
> +
> + /*
> + * Check that nothing bad happens when we kill the task in the middle
> + * of a syscall.
> + */
> + pid = fork();
> + ASSERT_GE(pid, 0);
> +
> + if (pid == 0) {
> + ret = syscall(__NR_getpid);
> + exit(ret != USER_NOTIF_MAGIC);
> + }
> +
> + EXPECT_EQ(ioctl(listener, SECCOMP_NOTIF_RECV, &req), sizeof(req));
> + EXPECT_EQ(ioctl(listener, SECCOMP_NOTIF_ID_VALID, &req.id), 0);
> +
> + EXPECT_EQ(kill(pid, SIGKILL), 0);
> + EXPECT_EQ(waitpid(pid, NULL, 0), pid);
> +
> + EXPECT_EQ(ioctl(listener, SECCOMP_NOTIF_ID_VALID, &req.id), -1);

Please document SECCOMP_NOTIF_ID_VALID in seccomp_filter.rst. I had
been wondering what it's for, and now I see it's kind of an advisory
"is the other end still alive?" test.

> +
> + resp.id = req.id;
> + ret = ioctl(listener, SECCOMP_NOTIF_SEND, &resp);
> + EXPECT_EQ(ret, -1);
> + EXPECT_EQ(errno, ENOENT);
> +
> + /*
> + * Check that we get another notification about a signal in the middle
> + * of a syscall.
> + */
> + pid = fork();
> + ASSERT_GE(pid, 0);
> +
> + if (pid == 0) {
> + if (signal(SIGUSR1, signal_handler) == SIG_ERR) {
> + perror("signal");
> + exit(1);
> + }
> + ret = syscall(__NR_getpid);
> + exit(ret != USER_NOTIF_MAGIC);
> + }
> +
> + ret = read_notif(listener, &req);
> + EXPECT_EQ(ret, sizeof(req));
> + EXPECT_EQ(errno, 0);
> +
> + EXPECT_EQ(kill(pid, SIGUSR1), 0);
> +
> + ret = read_notif(listener, &req);
> + EXPECT_EQ(req.signaled, 1);
> + EXPECT_EQ(ret, sizeof(req));
> + EXPECT_EQ(errno, 0);
> +
> + resp.len = sizeof(resp);
> + resp.id = req.id;
> + resp.error = -512; /* -ERESTARTSYS */
> + resp.val = 0;
> +
> + EXPECT_EQ(ioctl(listener, SECCOMP_NOTIF_SEND, &resp), sizeof(resp));
> +
> + ret = read_notif(listener, &req);
> + resp.len = sizeof(resp);
> + resp.id = req.id;
> + resp.error = 0;
> + resp.val = USER_NOTIF_MAGIC;
> + ret = ioctl(listener, SECCOMP_NOTIF_SEND, &resp);

I was slightly confused here: why have there been 3 reads? I was
expecting one notification for hitting getpid and one from catching a
signal. But in rereading, I see that NOTIF_RECV will return the most
recently unresponded notification, yes?

But... catching a signal replaces the existing seccomp_knotif? I
remain confused about how signal handling is meant to work here. What
happens if two signals get sent? It looks like you just block without
allowing more signals? (Thank you for writing the tests!)

(And can you document the expected behavior in the seccomp_filter.rst too?)

> + EXPECT_EQ(ret, sizeof(resp));
> + EXPECT_EQ(errno, 0);
> +
> + EXPECT_EQ(waitpid(pid, &status, 0), pid);
> + EXPECT_EQ(true, WIFEXITED(status));
> + EXPECT_EQ(0, WEXITSTATUS(status));
> +
> + /*
> + * Check that we get an ENOSYS when the listener is closed.
> + */
> + pid = fork();
> + ASSERT_GE(pid, 0);
> + if (pid == 0) {
> + close(listener);
> + ret = syscall(__NR_getpid);
> + exit(ret != -1 && errno != ENOSYS);
> + }
> +
> + close(listener);
> +
> + EXPECT_EQ(waitpid(pid, &status, 0), pid);
> + EXPECT_EQ(true, WIFEXITED(status));
> + EXPECT_EQ(0, WEXITSTATUS(status));
> +}
> +
> +/*
> + * Check that a pid in a child namespace still shows up as valid in ours.
> + */
> +TEST(user_notification_child_pid_ns)
> +{
> + pid_t pid;
> + int status, listener;
> + int sk_pair[2];
> + char c;
> + struct seccomp_notif req = {};
> + struct seccomp_notif_resp resp = {};
> +
> + ASSERT_EQ(socketpair(PF_LOCAL, SOCK_SEQPACKET, 0, sk_pair), 0);
> + ASSERT_EQ(unshare(CLONE_NEWPID), 0);
> +
> + pid = fork();
> + ASSERT_GE(pid, 0);
> +
> + if (pid == 0) {
> + EXPECT_EQ(user_trap_syscall(__NR_getpid, 0), 0);
> +
> + /* Signal we're ready and have installed the filter. */
> + EXPECT_EQ(write(sk_pair[1], "J", 1), 1);
> +
> + EXPECT_EQ(read(sk_pair[1], &c, 1), 1);
> + EXPECT_EQ(c, 'H');
> +
> + exit(syscall(__NR_getpid) != USER_NOTIF_MAGIC);
> + }
> +
> + EXPECT_EQ(read(sk_pair[0], &c, 1), 1);
> + EXPECT_EQ(c, 'J');
> +
> + EXPECT_EQ(ptrace(PTRACE_ATTACH, pid), 0);
> + EXPECT_EQ(waitpid(pid, NULL, 0), pid);
> + listener = ptrace(PTRACE_SECCOMP_NEW_LISTENER, pid, 0);
> + EXPECT_GE(listener, 0);
> + EXPECT_EQ(ptrace(PTRACE_DETACH, pid, NULL, 0), 0);
> +
> + /* Now signal we are done and respond with magic */
> + EXPECT_EQ(write(sk_pair[0], "H", 1), 1);
> +
> + req.len = sizeof(req);
> + EXPECT_EQ(ioctl(listener, SECCOMP_NOTIF_RECV, &req), sizeof(req));
> + EXPECT_EQ(req.pid, pid);
> +
> + resp.len = sizeof(resp);
> + resp.id = req.id;
> + resp.error = 0;
> + resp.val = USER_NOTIF_MAGIC;
> +
> + EXPECT_EQ(ioctl(listener, SECCOMP_NOTIF_SEND, &resp), sizeof(resp));
> +
> + EXPECT_EQ(waitpid(pid, &status, 0), pid);
> + EXPECT_EQ(true, WIFEXITED(status));
> + EXPECT_EQ(0, WEXITSTATUS(status));
> + close(listener);
> +}
> +
> +/*
> + * Check that a pid in a sibling (i.e. unrelated) namespace shows up as 0, i.e.
> + * invalid.
> + */
> +TEST(user_notification_sibling_pid_ns)
> +{
> + pid_t pid, pid2;
> + int status, listener;
> + int sk_pair[2];
> + char c;
> + struct seccomp_notif req = {};
> + struct seccomp_notif_resp resp = {};
> +
> + ASSERT_EQ(socketpair(PF_LOCAL, SOCK_SEQPACKET, 0, sk_pair), 0);
> +
> + pid = fork();
> + ASSERT_GE(pid, 0);
> +
> + if (pid == 0) {
> + int child_pair[2];
> +
> + ASSERT_EQ(unshare(CLONE_NEWPID), 0);
> +
> + ASSERT_EQ(socketpair(PF_LOCAL, SOCK_SEQPACKET, 0, child_pair), 0);
> +
> + pid2 = fork();
> + ASSERT_GE(pid2, 0);
> +
> + if (pid2 == 0) {
> + close(child_pair[0]);
> + EXPECT_EQ(user_trap_syscall(__NR_getpid, 0), 0);
> +
> + /* Signal we're ready and have installed the filter. */
> + EXPECT_EQ(write(child_pair[1], "J", 1), 1);
> +
> + EXPECT_EQ(read(child_pair[1], &c, 1), 1);
> + EXPECT_EQ(c, 'H');
> +
> + exit(syscall(__NR_getpid) != USER_NOTIF_MAGIC);
> + }
> +
> + /* check that child has installed the filter */
> + EXPECT_EQ(read(child_pair[0], &c, 1), 1);
> + EXPECT_EQ(c, 'J');
> +
> + /* tell parent who child is */
> + EXPECT_EQ(write(sk_pair[1], &pid2, sizeof(pid2)), sizeof(pid2));
> +
> + /* parent has installed listener, tell child to call syscall */
> + EXPECT_EQ(read(sk_pair[1], &c, 1), 1);
> + EXPECT_EQ(c, 'H');
> + EXPECT_EQ(write(child_pair[0], "H", 1), 1);
> +
> + EXPECT_EQ(waitpid(pid2, &status, 0), pid2);
> + EXPECT_EQ(true, WIFEXITED(status));
> + EXPECT_EQ(0, WEXITSTATUS(status));
> + exit(WEXITSTATUS(status));
> + }
> +
> + EXPECT_EQ(read(sk_pair[0], &pid2, sizeof(pid2)), sizeof(pid2));
> +
> + EXPECT_EQ(ptrace(PTRACE_ATTACH, pid2), 0);
> + EXPECT_EQ(waitpid(pid2, NULL, 0), pid2);
> + listener = ptrace(PTRACE_SECCOMP_NEW_LISTENER, pid2, 0);
> + EXPECT_GE(listener, 0);
> + EXPECT_EQ(errno, 0);
> + EXPECT_EQ(ptrace(PTRACE_DETACH, pid2, NULL, 0), 0);
> +
> + /* Create the sibling ns, and sibling in it. */
> + EXPECT_EQ(unshare(CLONE_NEWPID), 0);
> + EXPECT_EQ(errno, 0);
> +
> + pid2 = fork();
> + EXPECT_GE(pid2, 0);
> +
> + if (pid2 == 0) {
> + req.len = sizeof(req);
> + ASSERT_EQ(ioctl(listener, SECCOMP_NOTIF_RECV, &req), sizeof(req));
> + /*
> + * The pid should be 0, i.e. the task is in some namespace that
> + * we can't "see".
> + */
> + ASSERT_EQ(req.pid, 0);
> +
> + resp.len = sizeof(resp);
> + resp.id = req.id;
> + resp.error = 0;
> + resp.val = USER_NOTIF_MAGIC;
> +
> + ASSERT_EQ(ioctl(listener, SECCOMP_NOTIF_SEND, &resp), sizeof(resp));
> + exit(0);
> + }
> +
> + close(listener);
> +
> + /* Now signal we are done setting up sibling listener. */
> + EXPECT_EQ(write(sk_pair[0], "H", 1), 1);
> +
> + EXPECT_EQ(waitpid(pid, &status, 0), pid);
> + EXPECT_EQ(true, WIFEXITED(status));
> + EXPECT_EQ(0, WEXITSTATUS(status));
> +
> + EXPECT_EQ(waitpid(pid2, &status, 0), pid2);
> + EXPECT_EQ(true, WIFEXITED(status));
> + EXPECT_EQ(0, WEXITSTATUS(status));
> +}
> +
> +
> /*
> * TODO:
> * - add microbenchmarks
> --
> 2.17.1
>

Looking good!

-Kees

--
Kees Cook
Pixel Security