Re: [PATCH] netlink: add buffer boundary checking

[Mark Salyzyn]

On 7/24/20 2:14 PM, Jacob Keller wrote:
> On 7/23/2020 12:35 PM, Eric Dumazet wrote:
> > On 7/23/20 11:21 AM, Mark Salyzyn wrote:
> > > Many of the nla_get_* inlines fail to check attribute's length before
> > > copying the content resulting in possible out-of-boundary accesses.
> > > Adjust the inlines to perform nla_len checking, for the most part
> > > using the nla_memcpy function to faciliate since these are not
> > > necessarily performance critical and do not need a likely fast path.
> > >
> > > Signed-off-by: Mark Salyzyn <salyzyn@xxxxxxxxxxx>
> > > Cc: netdev@xxxxxxxxxxxxxxx
> > > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > > Cc: kernel-team@xxxxxxxxxxx
> > > Cc: "David S. Miller" <davem@xxxxxxxxxxxxx>
> > > Cc: Jakub Kicinski <kuba@xxxxxxxxxx>
> > > Cc: Thomas Graf <tgraf@xxxxxxx>
> > > Fixes: bfa83a9e03cf ("[NETLINK]: Type-safe netlink messages/attributes interface")
> > > ---
> > >   include/net/netlink.h | 66 +++++++++++++++++++++++++++++++++++--------
> > >   1 file changed, 54 insertions(+), 12 deletions(-)
> > >
> > > diff --git a/include/net/netlink.h b/include/net/netlink.h
> > > index c0411f14fb53..11c0f153be7c 100644
> > > --- a/include/net/netlink.h
> > > +++ b/include/net/netlink.h
> > > @@ -1538,7 +1538,11 @@ static inline int nla_put_bitfield32(struct sk_buff *skb, int attrtype,
> > >    */
> > >   static inline u32 nla_get_u32(const struct nlattr *nla)
> > >   {
> > > -	return *(u32 *) nla_data(nla);
> > > +	u32 tmp;
> > > +
> > > +	nla_memcpy(&tmp, nla, sizeof(tmp));
> > > +
> > > +	return tmp;
> > I believe this will hide bugs, that syzbot was able to catch.
> >
> > Instead, you could perhaps introduce a CONFIG_DEBUG_NETLINK option,
> > and add a WARN_ON_ONCE(nla_len(nla) < sizeof(u32)) so that we can detect bugs in callers.
> I also think this is a better approach.

We (another engineer here) are looking into that and will get back to 
everyone.

Sincerely -- Mark Salyzyn