| Message ID | 1378044450-8327-1-git-send-email-dh.herrmann@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi Dmitry On Sun, Sep 1, 2013 at 4:07 PM, David Herrmann <dh.herrmann@gmail.com> wrote: > If we have multiple sessions on a system, we normally don't want > background sessions to read input events. Otherwise, it could capture > passwords and more entered by the user on the foreground session. This is > a real world problem as the recent XMir development showed: > http://mjg59.dreamwidth.org/27327.html > > We currently rely on sessions to release input devices when being > deactivated. This relies on trust across sessions. But that's not given on > usual systems. We therefore need a way to control which processes have > access to input devices. > > With VTs the kernel simply routed them through the active /dev/ttyX. This > is not possible with evdev devices, though. Moreover, we want to avoid > routing input-devices through some dispatcher-daemon in userspace (which > would add some latency). > > This patch introduces EVIOCREVOKE. If called on an evdev fd, this revokes > device-access irrecoverably for that *single* open-file. Hence, once you > call EVIOCREVOKE on any dup()ed fd, all fds for that open-file will be > rather useless now (but still valid compared to close()!). This allows us > to pass fds directly to session-processes from a trusted source. The > source keeps a dup()ed fd and revokes access once the session-process is > no longer active. > Compared to the EVIOCMUTE proposal, we can avoid the CAP_SYS_ADMIN > restriction now as there is no way to revive the fd again. Hence, a user > is free to call EVIOCREVOKE themself to kill the fd. > > Additionally, this ioctl allows multi-layer access-control (again compared > to EVIOCMUTE which was limited to one layer via CAP_SYS_ADMIN). A middle > layer can simply request a new open-file from the layer above and pass it > to the layer below. Now each layer can call EVIOCREVOKE on the fds to > revoke access for all layers below, at the expense of one fd per layer. > > There's already ongoing experimental user-space work which demonstrates > how it can be used: > http://lists.freedesktop.org/archives/systemd-devel/2013-August/012897.html I've been running this logind-feature for some time on my machine now. I haven't seen any problems. Could you let us know what your plans are for this patch? 3.12 would be very nice so we could continue pushing the user-space parts. There are even existing programs (like weston-launch) which could already make great use of that with just a <10 line patch. Thanks David > Signed-off-by: David Herrmann <dh.herrmann@gmail.com> > --- > Changes from v2: > - Handle client->revoked like evdev->exist to avoid special-casing "revoked" > > drivers/input/evdev.c | 33 +++++++++++++++++++++++++++++---- > include/uapi/linux/input.h | 1 + > 2 files changed, 30 insertions(+), 4 deletions(-) > > diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c > index d2b34fb..cf6bdff 100644 > --- a/drivers/input/evdev.c > +++ b/drivers/input/evdev.c > @@ -48,6 +48,7 @@ struct evdev_client { > struct evdev *evdev; > struct list_head node; > int clkid; > + bool revoked; > unsigned int bufsize; > struct input_event buffer[]; > }; > @@ -164,6 +165,9 @@ static void evdev_pass_values(struct evdev_client *client, > struct input_event event; > bool wakeup = false; > > + if (client->revoked) > + return; > + > event.time = ktime_to_timeval(client->clkid == CLOCK_MONOTONIC ? > mono : real); > > @@ -429,7 +433,7 @@ static ssize_t evdev_write(struct file *file, const char __user *buffer, > if (retval) > return retval; > > - if (!evdev->exist) { > + if (!evdev->exist || client->revoked) { > retval = -ENODEV; > goto out; > } > @@ -511,7 +515,7 @@ static ssize_t evdev_read(struct file *file, char __user *buffer, > if (!(file->f_flags & O_NONBLOCK)) { > error = wait_event_interruptible(evdev->wait, > client->packet_head != client->tail || > - !evdev->exist); > + !evdev->exist || client->revoked); > if (error) > return error; > } > @@ -529,7 +533,11 @@ static unsigned int evdev_poll(struct file *file, poll_table *wait) > > poll_wait(file, &evdev->wait, wait); > > - mask = evdev->exist ? POLLOUT | POLLWRNORM : POLLHUP | POLLERR; > + if (evdev->exist && !client->revoked) > + mask = POLLOUT | POLLWRNORM; > + else > + mask = POLLHUP | POLLERR; > + > if (client->packet_head != client->tail) > mask |= POLLIN | POLLRDNORM; > > @@ -795,6 +803,17 @@ static int evdev_handle_mt_request(struct input_dev *dev, > return 0; > } > > +static int evdev_revoke(struct evdev *evdev, struct evdev_client *client, > + struct file *file) > +{ > + client->revoked = true; > + evdev_ungrab(evdev, client); > + input_flush_device(&evdev->handle, file); > + wake_up_interruptible(&evdev->wait); > + > + return 0; > +} > + > static long evdev_do_ioctl(struct file *file, unsigned int cmd, > void __user *p, int compat_mode) > { > @@ -857,6 +876,12 @@ static long evdev_do_ioctl(struct file *file, unsigned int cmd, > else > return evdev_ungrab(evdev, client); > > + case EVIOCREVOKE: > + if (p) > + return -EINVAL; > + else > + return evdev_revoke(evdev, client, file); > + > case EVIOCSCLOCKID: > if (copy_from_user(&i, p, sizeof(unsigned int))) > return -EFAULT; > @@ -1002,7 +1027,7 @@ static long evdev_ioctl_handler(struct file *file, unsigned int cmd, > if (retval) > return retval; > > - if (!evdev->exist) { > + if (!evdev->exist || client->revoked) { > retval = -ENODEV; > goto out; > } > diff --git a/include/uapi/linux/input.h b/include/uapi/linux/input.h > index 2fb6fae..d61c61c 100644 > --- a/include/uapi/linux/input.h > +++ b/include/uapi/linux/input.h > @@ -152,6 +152,7 @@ struct input_keymap_entry { > #define EVIOCGEFFECTS _IOR('E', 0x84, int) /* Report number of effects playable at the same time */ > > #define EVIOCGRAB _IOW('E', 0x90, int) /* Grab/Release device */ > +#define EVIOCREVOKE _IOW('E', 0x91, int) /* Revoke device access */ > > #define EVIOCSCLOCKID _IOW('E', 0xa0, int) /* Set clockid to be used for timestamps */ > > -- > 1.8.4 > -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Fri, Sep 6, 2013 at 10:12 AM, David Herrmann <dh.herrmann@gmail.com> wrote: > Hi Dmitry > > On Sun, Sep 1, 2013 at 4:07 PM, David Herrmann <dh.herrmann@gmail.com> wrote: >> If we have multiple sessions on a system, we normally don't want >> background sessions to read input events. Otherwise, it could capture >> passwords and more entered by the user on the foreground session. This is >> a real world problem as the recent XMir development showed: >> http://mjg59.dreamwidth.org/27327.html >> >> We currently rely on sessions to release input devices when being >> deactivated. This relies on trust across sessions. But that's not given on >> usual systems. We therefore need a way to control which processes have >> access to input devices. >> >> With VTs the kernel simply routed them through the active /dev/ttyX. This >> is not possible with evdev devices, though. Moreover, we want to avoid >> routing input-devices through some dispatcher-daemon in userspace (which >> would add some latency). >> >> This patch introduces EVIOCREVOKE. If called on an evdev fd, this revokes >> device-access irrecoverably for that *single* open-file. Hence, once you >> call EVIOCREVOKE on any dup()ed fd, all fds for that open-file will be >> rather useless now (but still valid compared to close()!). This allows us >> to pass fds directly to session-processes from a trusted source. The >> source keeps a dup()ed fd and revokes access once the session-process is >> no longer active. >> Compared to the EVIOCMUTE proposal, we can avoid the CAP_SYS_ADMIN >> restriction now as there is no way to revive the fd again. Hence, a user >> is free to call EVIOCREVOKE themself to kill the fd. >> >> Additionally, this ioctl allows multi-layer access-control (again compared >> to EVIOCMUTE which was limited to one layer via CAP_SYS_ADMIN). A middle >> layer can simply request a new open-file from the layer above and pass it >> to the layer below. Now each layer can call EVIOCREVOKE on the fds to >> revoke access for all layers below, at the expense of one fd per layer. >> >> There's already ongoing experimental user-space work which demonstrates >> how it can be used: >> http://lists.freedesktop.org/archives/systemd-devel/2013-August/012897.html > > I've been running this logind-feature for some time on my machine now. > I haven't seen any problems. Could you let us know what your plans are > for this patch? > 3.12 would be very nice so we could continue pushing the user-space parts. > There are even existing programs (like weston-launch) which could > already make great use of that with just a <10 line patch. I think we have good use cases for this - with revoke we can give input fds to a non-trusted, non-root display-severs and standalone KMS+evdev applications and reliably revoke them when their session is deactivated (vt switched away typically). EVIOCREVOKE is usable in logind and standalone setuid helpers such as weston-launch,. Everything other priviledge operation a display server needs can be done in logind or weston-launch, this ioctl is the final piece that lets us run X without root priviledges. Reviewed-by: Kristian Høgsberg <krh@bitplanet.net> >> Signed-off-by: David Herrmann <dh.herrmann@gmail.com> >> --- >> Changes from v2: >> - Handle client->revoked like evdev->exist to avoid special-casing "revoked" >> >> drivers/input/evdev.c | 33 +++++++++++++++++++++++++++++---- >> include/uapi/linux/input.h | 1 + >> 2 files changed, 30 insertions(+), 4 deletions(-) >> >> diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c >> index d2b34fb..cf6bdff 100644 >> --- a/drivers/input/evdev.c >> +++ b/drivers/input/evdev.c >> @@ -48,6 +48,7 @@ struct evdev_client { >> struct evdev *evdev; >> struct list_head node; >> int clkid; >> + bool revoked; >> unsigned int bufsize; >> struct input_event buffer[]; >> }; >> @@ -164,6 +165,9 @@ static void evdev_pass_values(struct evdev_client *client, >> struct input_event event; >> bool wakeup = false; >> >> + if (client->revoked) >> + return; >> + >> event.time = ktime_to_timeval(client->clkid == CLOCK_MONOTONIC ? >> mono : real); >> >> @@ -429,7 +433,7 @@ static ssize_t evdev_write(struct file *file, const char __user *buffer, >> if (retval) >> return retval; >> >> - if (!evdev->exist) { >> + if (!evdev->exist || client->revoked) { >> retval = -ENODEV; >> goto out; >> } >> @@ -511,7 +515,7 @@ static ssize_t evdev_read(struct file *file, char __user *buffer, >> if (!(file->f_flags & O_NONBLOCK)) { >> error = wait_event_interruptible(evdev->wait, >> client->packet_head != client->tail || >> - !evdev->exist); >> + !evdev->exist || client->revoked); >> if (error) >> return error; >> } >> @@ -529,7 +533,11 @@ static unsigned int evdev_poll(struct file *file, poll_table *wait) >> >> poll_wait(file, &evdev->wait, wait); >> >> - mask = evdev->exist ? POLLOUT | POLLWRNORM : POLLHUP | POLLERR; >> + if (evdev->exist && !client->revoked) >> + mask = POLLOUT | POLLWRNORM; >> + else >> + mask = POLLHUP | POLLERR; >> + >> if (client->packet_head != client->tail) >> mask |= POLLIN | POLLRDNORM; >> >> @@ -795,6 +803,17 @@ static int evdev_handle_mt_request(struct input_dev *dev, >> return 0; >> } >> >> +static int evdev_revoke(struct evdev *evdev, struct evdev_client *client, >> + struct file *file) >> +{ >> + client->revoked = true; >> + evdev_ungrab(evdev, client); >> + input_flush_device(&evdev->handle, file); >> + wake_up_interruptible(&evdev->wait); >> + >> + return 0; >> +} >> + >> static long evdev_do_ioctl(struct file *file, unsigned int cmd, >> void __user *p, int compat_mode) >> { >> @@ -857,6 +876,12 @@ static long evdev_do_ioctl(struct file *file, unsigned int cmd, >> else >> return evdev_ungrab(evdev, client); >> >> + case EVIOCREVOKE: >> + if (p) >> + return -EINVAL; >> + else >> + return evdev_revoke(evdev, client, file); >> + >> case EVIOCSCLOCKID: >> if (copy_from_user(&i, p, sizeof(unsigned int))) >> return -EFAULT; >> @@ -1002,7 +1027,7 @@ static long evdev_ioctl_handler(struct file *file, unsigned int cmd, >> if (retval) >> return retval; >> >> - if (!evdev->exist) { >> + if (!evdev->exist || client->revoked) { >> retval = -ENODEV; >> goto out; >> } >> diff --git a/include/uapi/linux/input.h b/include/uapi/linux/input.h >> index 2fb6fae..d61c61c 100644 >> --- a/include/uapi/linux/input.h >> +++ b/include/uapi/linux/input.h >> @@ -152,6 +152,7 @@ struct input_keymap_entry { >> #define EVIOCGEFFECTS _IOR('E', 0x84, int) /* Report number of effects playable at the same time */ >> >> #define EVIOCGRAB _IOW('E', 0x90, int) /* Grab/Release device */ >> +#define EVIOCREVOKE _IOW('E', 0x91, int) /* Revoke device access */ >> >> #define EVIOCSCLOCKID _IOW('E', 0xa0, int) /* Set clockid to be used for timestamps */ >> >> -- >> 1.8.4 >> -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c index d2b34fb..cf6bdff 100644 --- a/drivers/input/evdev.c +++ b/drivers/input/evdev.c @@ -48,6 +48,7 @@ struct evdev_client { struct evdev *evdev; struct list_head node; int clkid; + bool revoked; unsigned int bufsize; struct input_event buffer[]; }; @@ -164,6 +165,9 @@ static void evdev_pass_values(struct evdev_client *client, struct input_event event; bool wakeup = false; + if (client->revoked) + return; + event.time = ktime_to_timeval(client->clkid == CLOCK_MONOTONIC ? mono : real); @@ -429,7 +433,7 @@ static ssize_t evdev_write(struct file *file, const char __user *buffer, if (retval) return retval; - if (!evdev->exist) { + if (!evdev->exist || client->revoked) { retval = -ENODEV; goto out; } @@ -511,7 +515,7 @@ static ssize_t evdev_read(struct file *file, char __user *buffer, if (!(file->f_flags & O_NONBLOCK)) { error = wait_event_interruptible(evdev->wait, client->packet_head != client->tail || - !evdev->exist); + !evdev->exist || client->revoked); if (error) return error; } @@ -529,7 +533,11 @@ static unsigned int evdev_poll(struct file *file, poll_table *wait) poll_wait(file, &evdev->wait, wait); - mask = evdev->exist ? POLLOUT | POLLWRNORM : POLLHUP | POLLERR; + if (evdev->exist && !client->revoked) + mask = POLLOUT | POLLWRNORM; + else + mask = POLLHUP | POLLERR; + if (client->packet_head != client->tail) mask |= POLLIN | POLLRDNORM; @@ -795,6 +803,17 @@ static int evdev_handle_mt_request(struct input_dev *dev, return 0; } +static int evdev_revoke(struct evdev *evdev, struct evdev_client *client, + struct file *file) +{ + client->revoked = true; + evdev_ungrab(evdev, client); + input_flush_device(&evdev->handle, file); + wake_up_interruptible(&evdev->wait); + + return 0; +} + static long evdev_do_ioctl(struct file *file, unsigned int cmd, void __user *p, int compat_mode) { @@ -857,6 +876,12 @@ static long evdev_do_ioctl(struct file *file, unsigned int cmd, else return evdev_ungrab(evdev, client); + case EVIOCREVOKE: + if (p) + return -EINVAL; + else + return evdev_revoke(evdev, client, file); + case EVIOCSCLOCKID: if (copy_from_user(&i, p, sizeof(unsigned int))) return -EFAULT; @@ -1002,7 +1027,7 @@ static long evdev_ioctl_handler(struct file *file, unsigned int cmd, if (retval) return retval; - if (!evdev->exist) { + if (!evdev->exist || client->revoked) { retval = -ENODEV; goto out; } diff --git a/include/uapi/linux/input.h b/include/uapi/linux/input.h index 2fb6fae..d61c61c 100644 --- a/include/uapi/linux/input.h +++ b/include/uapi/linux/input.h @@ -152,6 +152,7 @@ struct input_keymap_entry { #define EVIOCGEFFECTS _IOR('E', 0x84, int) /* Report number of effects playable at the same time */ #define EVIOCGRAB _IOW('E', 0x90, int) /* Grab/Release device */ +#define EVIOCREVOKE _IOW('E', 0x91, int) /* Revoke device access */ #define EVIOCSCLOCKID _IOW('E', 0xa0, int) /* Set clockid to be used for timestamps */
If we have multiple sessions on a system, we normally don't want background sessions to read input events. Otherwise, it could capture passwords and more entered by the user on the foreground session. This is a real world problem as the recent XMir development showed: http://mjg59.dreamwidth.org/27327.html We currently rely on sessions to release input devices when being deactivated. This relies on trust across sessions. But that's not given on usual systems. We therefore need a way to control which processes have access to input devices. With VTs the kernel simply routed them through the active /dev/ttyX. This is not possible with evdev devices, though. Moreover, we want to avoid routing input-devices through some dispatcher-daemon in userspace (which would add some latency). This patch introduces EVIOCREVOKE. If called on an evdev fd, this revokes device-access irrecoverably for that *single* open-file. Hence, once you call EVIOCREVOKE on any dup()ed fd, all fds for that open-file will be rather useless now (but still valid compared to close()!). This allows us to pass fds directly to session-processes from a trusted source. The source keeps a dup()ed fd and revokes access once the session-process is no longer active. Compared to the EVIOCMUTE proposal, we can avoid the CAP_SYS_ADMIN restriction now as there is no way to revive the fd again. Hence, a user is free to call EVIOCREVOKE themself to kill the fd. Additionally, this ioctl allows multi-layer access-control (again compared to EVIOCMUTE which was limited to one layer via CAP_SYS_ADMIN). A middle layer can simply request a new open-file from the layer above and pass it to the layer below. Now each layer can call EVIOCREVOKE on the fds to revoke access for all layers below, at the expense of one fd per layer. There's already ongoing experimental user-space work which demonstrates how it can be used: http://lists.freedesktop.org/archives/systemd-devel/2013-August/012897.html Signed-off-by: David Herrmann <dh.herrmann@gmail.com> --- Changes from v2: - Handle client->revoked like evdev->exist to avoid special-casing "revoked" drivers/input/evdev.c | 33 +++++++++++++++++++++++++++++---- include/uapi/linux/input.h | 1 + 2 files changed, 30 insertions(+), 4 deletions(-)