On Wed, Dec 25, 2019 at 09:45:33PM +0000, Sargun Dhillon wrote: > This patch is a small change in enforcement of the uapi for > SECCOMP_IOCTL_NOTIF_RECV ioctl. Specificaly, the datastructure which is > passed (seccomp_notif), has a flags member. Previously that could be > set to a nonsense value, and we would ignore it. This ensures that > no flags are set. > > Signed-off-by: Sargun Dhillon <sargun@xxxxxxxxx> > Cc: Kees Cook <keescook@xxxxxxxxxxxx> I'm fine with this since we soon want to make use of the flag argument when we add a flag to get a pidfd from the seccomp notifier on receive. The major users I could identify already pass in seccomp_notif with all fields set to 0. If we really break users we can always revert; this seems very unlikely to me though. One more question below, otherwise: Reviewed-by: Christian Brauner <christian.brauner@xxxxxxxxxx> > --- > kernel/seccomp.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/kernel/seccomp.c b/kernel/seccomp.c > index 12d2227e5786..455925557490 100644 > --- a/kernel/seccomp.c > +++ b/kernel/seccomp.c > @@ -1026,6 +1026,13 @@ static long seccomp_notify_recv(struct seccomp_filter *filter, > struct seccomp_notif unotif; > ssize_t ret; > > + if (copy_from_user(&unotif, buf, sizeof(unotif))) > + return -EFAULT; > + > + /* flags is reserved right now, make sure it's unset */ > + if (unotif.flags) > + return -EINVAL; > + Might it make sense to use err = copy_struct_from_user(&unotif, sizeof(unotif), buf, sizeof(unotif)); if (err) return err; This way we check that the whole struct is 0 and report an error as soon as one of the members is non-zero. That's more drastic but it'd ensure that other fields can be used in the future for whatever purposes. It would also let us get rid of the memset() below. > memset(&unotif, 0, sizeof(unotif)); > > ret = down_interruptible(&filter->notif->request); > -- > 2.20.1 >
