netdev - Re: [PATCH] net/ipv4: Replace tcp_ca_get_name_by

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Message-ID: <202407132108.1577A694@keescook>
Date: Sat, 13 Jul 2024 21:09:10 -0700
From: Kees Cook <kees@...nel.org>
To: Eric Dumazet <edumazet@...gle.com>
Cc: "David S. Miller" <davem@...emloft.net>,
	David Ahern <dsahern@...nel.org>, Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH] net/ipv4: Replace tcp_ca_get_name_by_key()'s strncpy()
 with strscpy()

On Thu, Jul 11, 2024 at 10:38:01AM -0700, Eric Dumazet wrote:
> On Thu, Jul 11, 2024 at 10:16 AM Kees Cook <kees@...nel.org> wrote:
> >
> > Replace the deprecated[1] use of strncpy() in tcp_ca_get_name_by_key().
> > The only caller passes the results to nla_put_string(), so trailing
> > padding is not needed.
> >
> > Since passing "buffer" decays it to a pointer, the size can't be
> > trivially determined by the compiler. ca->name is the same length,
> > so strscpy() won't fail (when ca->name is NUL-terminated). Include the
> > length explicitly instead of using the 2-argument strscpy().
> >
> > Link: https://github.com/KSPP/linux/issues/90 [1]
> > Signed-off-by: Kees Cook <kees@...nel.org>
> > ---
> > Cc: Eric Dumazet <edumazet@...gle.com>
> > Cc: "David S. Miller" <davem@...emloft.net>
> > Cc: David Ahern <dsahern@...nel.org>
> > Cc: Jakub Kicinski <kuba@...nel.org>
> > Cc: Paolo Abeni <pabeni@...hat.com>
> > Cc: netdev@...r.kernel.org
> > ---
> >  net/ipv4/tcp_cong.c | 7 ++++---
> >  1 file changed, 4 insertions(+), 3 deletions(-)
> >
> > diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
> > index 28ffcfbeef14..2a303a7cba59 100644
> > --- a/net/ipv4/tcp_cong.c
> > +++ b/net/ipv4/tcp_cong.c
> > @@ -203,9 +203,10 @@ char *tcp_ca_get_name_by_key(u32 key, char *buffer)
> >
> >         rcu_read_lock();
> >         ca = tcp_ca_find_key(key);
> > -       if (ca)
> > -               ret = strncpy(buffer, ca->name,
> > -                             TCP_CA_NAME_MAX);
> > +       if (ca) {
> > +               strscpy(buffer, ca->name, TCP_CA_NAME_MAX);
> > +               ret = buffer;
> > +       }
> >         rcu_read_unlock();
> >
> 
> Ok, but what about tcp_get_default_congestion_control() ?

Whoops. Yes. I'll do that at the same time. v2 coming...

-- 
Kees Cook