From: Sargun Dhillon sargun@sargun.me
commit ddc473916955f7710d1eb17c1273d91c8622a9fe upstream.
This refactors the user notification code to have a do / while loop around the completion condition. This has a small change in semantic, in that previously we ignored addfd calls upon wakeup if the notification had been responded to, but instead with the new change we check for an outstanding addfd calls prior to returning to userspace.
Rodrigo Campos also identified a bug that can result in addfd causing an early return, when the supervisor didn't actually handle the syscall [1].
[1]: https://lore.kernel.org/lkml/20210413160151.3301-1-rodrigo@kinvolk.io/
Fixes: 7cf97b125455 ("seccomp: Introduce addfd ioctl to seccomp user notifier") Signed-off-by: Sargun Dhillon sargun@sargun.me Acked-by: Tycho Andersen tycho@tycho.pizza Acked-by: Christian Brauner christian.brauner@ubuntu.com Signed-off-by: Kees Cook keescook@chromium.org Tested-by: Rodrigo Campos rodrigo@kinvolk.io Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20210517193908.3113-3-sargun@sargun.me Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- kernel/seccomp.c | 30 ++++++++++++++++-------------- 1 file changed, 16 insertions(+), 14 deletions(-)
--- a/kernel/seccomp.c +++ b/kernel/seccomp.c @@ -864,28 +864,30 @@ static int seccomp_do_user_notification(
up(&match->notif->request); wake_up_poll(&match->wqh, EPOLLIN | EPOLLRDNORM); - mutex_unlock(&match->notify_lock);
/* * This is where we wait for a reply from userspace. */ -wait: - err = wait_for_completion_interruptible(&n.ready); - mutex_lock(&match->notify_lock); - if (err == 0) { - /* Check if we were woken up by a addfd message */ + do { + mutex_unlock(&match->notify_lock); + err = wait_for_completion_interruptible(&n.ready); + mutex_lock(&match->notify_lock); + if (err != 0) + goto interrupted; + addfd = list_first_entry_or_null(&n.addfd, struct seccomp_kaddfd, list); - if (addfd && n.state != SECCOMP_NOTIFY_REPLIED) { + /* Check if we were woken up by a addfd message */ + if (addfd) seccomp_handle_addfd(addfd); - mutex_unlock(&match->notify_lock); - goto wait; - } - ret = n.val; - err = n.error; - flags = n.flags; - }
+ } while (n.state != SECCOMP_NOTIFY_REPLIED); + + ret = n.val; + err = n.error; + flags = n.flags; + +interrupted: /* If there were any pending addfd calls, clear them out */ list_for_each_entry_safe(addfd, tmp, &n.addfd, list) { /* The process went away before we got a chance to handle it */