Re: [PATCH net] net, neigh: clear whole pneigh_entry at alloc time

From: Eric Dumazet <edumazet@google.com>
To: David Ahern <dsahern@gmail.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>,
	"David S . Miller" <davem@davemloft.net>,
	Jakub Kicinski <kuba@kernel.org>, netdev <netdev@vger.kernel.org>,
	Roopa Prabhu <roopa@nvidia.com>
Subject: Re: [PATCH net] net, neigh: clear whole pneigh_entry at alloc time
Date: Wed, 8 Dec 2021 10:36:25 -0800	[thread overview]
Message-ID: <CANn89iLcHVUW1jHjWesL+Esi-tE3OJNEv5h=riuZq3jA1n+jhw@mail.gmail.com> (raw)
In-Reply-To: <ded3d280-efcd-810e-c29c-7296f97cb181@gmail.com>

On Wed, Dec 8, 2021 at 7:54 AM David Ahern <dsahern@gmail.com> wrote:
>
> On 12/6/21 9:53 AM, Eric Dumazet wrote:
> > From: Eric Dumazet <edumazet@google.com>
> >
> > Commit 2c611ad97a82 ("net, neigh: Extend neigh->flags to 32 bit
> > to allow for extensions") enables a new KMSAM warning [1]
> >
> > I think the bug is actually older, because the following intruction
> > only occurred if ndm->ndm_flags had NTF_PROXY set.
> >
> >       pn->flags = ndm->ndm_flags;
> >
> > Let's clear all pneigh_entry fields at alloc time.
> >
>
> All of the fields - except the new flags field - are initialized after
> the alloc. Why do you think the bug is older?

Because the flags field was added earlier, in the commit I pointed in Fixes: tag

For some reason, syzbot found the issue only after Roopa patch went in.
But we need to backport to older versions I think, or risk a kernel-info-leak

>
> ...
>
> > Fixes: 62dd93181aaa ("[IPV6] NDISC: Set per-entry is_router flag in Proxy NA.")
> > Signed-off-by: Eric Dumazet <edumazet@google.com>
> > Cc: Roopa Prabhu <roopa@nvidia.com>
> > ---
> >  net/core/neighbour.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/net/core/neighbour.c b/net/core/neighbour.c
> > index 72ba027c34cfea6f38a9e78927c35048ebfe7a7f..dda12fbd177ba6ad2798ea2b07733fa3f03441ab 100644
> > --- a/net/core/neighbour.c
> > +++ b/net/core/neighbour.c
> > @@ -763,11 +763,10 @@ struct pneigh_entry * pneigh_lookup(struct neigh_table *tbl,
> >
> >       ASSERT_RTNL();
> >
> > -     n = kmalloc(sizeof(*n) + key_len, GFP_KERNEL);
> > +     n = kzalloc(sizeof(*n) + key_len, GFP_KERNEL);
> >       if (!n)
> >               goto out;
> >
> > -     n->protocol = 0;
> >       write_pnet(&n->net, net);
> >       memcpy(n->key, pkey, key_len);
> >       n->dev = dev;
> >
>
> Reviewed-by: David Ahern <dsahern@kernel.org>