On 2019-12-26, Christian Brauner <christian.brauner@xxxxxxxxxx> wrote: > 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. Given that this isn't an extensible struct, it would be simpler to just do check_zeroed_user() -- copy_struct_from_user() is overkill. That would also remove the need for any copy_from_user()s and the memset can be dropped by just doing struct seccomp_notif unotif = {}; > > memset(&unotif, 0, sizeof(unotif)); > > > > ret = down_interruptible(&filter->notif->request); > > -- > > 2.20.1 > > -- Aleksa Sarai Senior Software Engineer (Containers) SUSE Linux GmbH <https://www.cyphar.com/>
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