netdev - Re: [PATCH] net: check the return value of the copy_from

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Message-ID: <CANn89i+zW+t1OEs2ut9Zm6FweY869Yrn-fnjq38tcmqqHLaTvA@mail.gmail.com>
Date: Wed, 11 Sep 2024 14:40:47 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Qianqiang Liu <qianqiang.liu@....com>
Cc: Tze-nan.Wu@...iatek.com, xiyou.wangcong@...il.com, davem@...emloft.net, 
	kuba@...nel.org, pabeni@...hat.com, netdev@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: check the return value of the copy_from_sockptr

On Wed, Sep 11, 2024 at 1:14 PM Qianqiang Liu <qianqiang.liu@....com> wrote:
>
> On Wed, Sep 11, 2024 at 11:12:24AM +0200, Eric Dumazet wrote:
> > On Wed, Sep 11, 2024 at 10:23 AM Qianqiang Liu <qianqiang.liu@....com> wrote:
> > >
> > > > I do not think it matters, because the copy is performed later, with
> > > > all the needed checks.
> > >
> > > No, there is no checks at all.
> > >
> >
> > Please elaborate ?
> > Why should maintainers have to spend time to provide evidence to
> > support your claims ?
> > Have you thought about the (compat) case ?
> >
> > There are plenty of checks. They were there before Stanislav commit.
> >
> > Each getsockopt() handler must perform the same actions.
> >
> > For instance, look at do_ipv6_getsockopt()
> >
> > If you find one getsockopt() method failing to perform the checks,
> > please report to us.
>
> Sorry, let me explain a little bit.
>
> The issue was introduced in this commit: 33f339a1ba54e ("bpf, net: Fix a
> potential race in do_sock_getsockopt()")

Not really.

Code before this commit also ignored copy_from_sockptr() return code.

>
> diff --git a/net/socket.c b/net/socket.c
> index fcbdd5bc47ac..0a2bd22ec105 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -2362,7 +2362,7 @@ INDIRECT_CALLABLE_DECLARE(bool tcp_bpf_bypass_getsockopt(int level,
>  int do_sock_getsockopt(struct socket *sock, bool compat, int level,
>                        int optname, sockptr_t optval, sockptr_t optlen)
>  {
> -       int max_optlen __maybe_unused;
> +       int max_optlen __maybe_unused = 0;
>         const struct proto_ops *ops;
>         int err;
>
> @@ -2371,7 +2371,7 @@ int do_sock_getsockopt(struct socket *sock, bool compat, int level,
>                 return err;
>
>         if (!compat)
> -               max_optlen = BPF_CGROUP_GETSOCKOPT_MAX_OPTLEN(optlen);
> +               copy_from_sockptr(&max_optlen, optlen, sizeof(int));
>
>         ops = READ_ONCE(sock->ops);
>         if (level == SOL_SOCKET) {
>
> The return value of "copy_from_sockptr()" in "do_sock_getsockopt()" was
> not checked. So, I added the following patch:
>
> diff --git a/net/socket.c b/net/socket.c
> index 0a2bd22ec105..6b9a414d01d5 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -2370,8 +2370,11 @@ int do_sock_getsockopt(struct socket *sock, bool compat, int level,
>         if (err)
>                 return err;
>
> -       if (!compat)
> -               copy_from_sockptr(&max_optlen, optlen, sizeof(int));
> +       if (!compat) {
> +               err = copy_from_sockptr(&max_optlen, optlen, sizeof(int));
> +               if (err)
> +                       return -EFAULT;
> +       }
>
>         ops = READ_ONCE(sock->ops);
>         if (level == SOL_SOCKET) {
>
> Maybe I missed something?
>
> If you think it's not an issue, then I'm OK with it.

It is not an issue, just adding extra code for an unlikely condition
that must be tested later anyway.