On Thu, Jan 09, 2025 at 02:31:37AM -0500, Michael S. Tsirkin wrote: > On Thu, Jan 09, 2025 at 03:58:44PM +0900, Akihiko Odaki wrote: > > tun used to simply advance iov_iter when it needs to pad virtio header, > > which leaves the garbage in the buffer as is. This is especially > > problematic when tun starts to allow enabling the hash reporting > > feature; even if the feature is enabled, the packet may lack a hash > > value and may contain a hole in the virtio header because the packet > > arrived before the feature gets enabled or does not contain the > > header fields to be hashed. If the hole is not filled with zero, it is > > impossible to tell if the packet lacks a hash value. > > > > In theory, a user of tun can fill the buffer with zero before calling > > read() to avoid such a problem, but leaving the garbage in the buffer is > > awkward anyway so fill the buffer in tun. > > > > Signed-off-by: Akihiko Odaki <akihiko.odaki@xxxxxxxxxx> > > But if the user did it, you have just overwritten his value, > did you not? To clearify, I mean if user pre-filled buffer with 1, you have now regressed it. Patch 3 fixes it back, but - not pretty. > > --- > > drivers/net/tun_vnet.c | 3 ++- > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/net/tun_vnet.c b/drivers/net/tun_vnet.c > > index fe842df9e9ef..ffb2186facd3 100644 > > --- a/drivers/net/tun_vnet.c > > +++ b/drivers/net/tun_vnet.c > > @@ -138,7 +138,8 @@ int tun_vnet_hdr_put(int sz, struct iov_iter *iter, > > if (copy_to_iter(hdr, sizeof(*hdr), iter) != sizeof(*hdr)) > > return -EFAULT; > > > > - iov_iter_advance(iter, sz - sizeof(*hdr)); > > + if (iov_iter_zero(sz - sizeof(*hdr), iter) != sz - sizeof(*hdr)) > > + return -EFAULT; > > > > return 0; > > } > > > > -- > > 2.47.1
