On Sun, 7 Feb 2021 10:26:54 +0200 Leon Romanovsky wrote: > On Sat, Feb 06, 2021 at 03:28:28PM -0800, Jakub Kicinski wrote: > > On Sat, 6 Feb 2021 12:36:48 -0800 Arjun Roy wrote: > > > From: Arjun Roy <arjun...@google.com> > > > > > > Explicitly define reserved field and require it to be 0-valued. > > > > > diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c > > > index e1a17c6b473c..c8469c579ed8 100644 > > > --- a/net/ipv4/tcp.c > > > +++ b/net/ipv4/tcp.c > > > @@ -4159,6 +4159,8 @@ static int do_tcp_getsockopt(struct sock *sk, int > > > level, > > > } > > > if (copy_from_user(&zc, optval, len)) > > > return -EFAULT; > > > + if (zc.reserved) > > > + return -EINVAL; > > > lock_sock(sk); > > > err = tcp_zerocopy_receive(sk, &zc, &tss); > > > release_sock(sk); > > > > I was expecting we'd also throw in a check_zeroed_user(). > > Either we can check if the buffer is zeroed all the way, > > or we can't and we shouldn't validate reserved either > > > > check_zeroed_user(optval + offsetof(reserved), > > len - offsetof(reserved)) > > ? > > There is a check that len is not larger than zs and users can't give > large buffer. > > I would say that is pretty safe to write "if (zc.reserved)".
Which check? There's a check which truncates (writes back to user space len = min(len, sizeof(zc)). Application can still pass garbage beyond sizeof(zc) and syscall may start failing in the future if sizeof(zc) changes.
