[PATCH] net: Check the argument for listen(2)

[PATCH] net: Check the argument for listen(2)

[Changli Gao]

As we use u16 to save the value of the argument for listen(2),
we'd better check if the value is larger than SINT_MAX other
than cut it down silently on error.
---
 net/ipv4/af_inet.c |    3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
index b4d0be2..35aaf00 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -198,6 +198,9 @@ int inet_listen(struct socket *sock, int backlog)
 	unsigned char old_state;
 	int err;
 
+	if (backlog >= (1 << 16))
+		return EINVAL;
+
 	lock_sock(sk);
 
 	err = -EINVAL;
-- 
1.7.9.5

Re: [PATCH] net: Check the argument for listen(2)

[Eric Dumazet]

On Sat, 2013-06-29 at 00:14 +0800, Changli Gao wrote:
> As we use u16 to save the value of the argument for listen(2),
> we'd better check if the value is larger than SINT_MAX other
> than cut it down silently on error.
> ---
>  net/ipv4/af_inet.c |    3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
> index b4d0be2..35aaf00 100644
> --- a/net/ipv4/af_inet.c
> +++ b/net/ipv4/af_inet.c
> @@ -198,6 +198,9 @@ int inet_listen(struct socket *sock, int backlog)
>  	unsigned char old_state;
>  	int err;
>  
> +	if (backlog >= (1 << 16))
> +		return EINVAL;
> +
>  	lock_sock(sk);
>  
>  	err = -EINVAL;

This seems pretty buggy to me.

1) EINVAL is not -EINVAL

2) This might break existing applications.

Re: [PATCH] net: Check the argument for listen(2)

[Hannes Frederic Sowa]

On Fri, Jun 28, 2013 at 09:29:02AM -0700, Eric Dumazet wrote:
> On Sat, 2013-06-29 at 00:14 +0800, Changli Gao wrote:
> > --- a/net/ipv4/af_inet.c
> > +++ b/net/ipv4/af_inet.c
> > @@ -198,6 +198,9 @@ int inet_listen(struct socket *sock, int backlog)
> >  	unsigned char old_state;
> >  	int err;
> >  
> > +	if (backlog >= (1 << 16))
> > +		return EINVAL;
> > +
> >  	lock_sock(sk);
> >  
> >  	err = -EINVAL;
> 
> This seems pretty buggy to me.
> 
> 1) EINVAL is not -EINVAL
> 
> 2) This might break existing applications.

Yes, we should clamp the value to netdev_max_backlog.

Greetings,

  Hannes

Re: [PATCH] net: Check the argument for listen(2)

[Hannes Frederic Sowa]

On Fri, Jun 28, 2013 at 06:32:34PM +0200, Hannes Frederic Sowa wrote:
> On Fri, Jun 28, 2013 at 09:29:02AM -0700, Eric Dumazet wrote:
> > On Sat, 2013-06-29 at 00:14 +0800, Changli Gao wrote:
> > > --- a/net/ipv4/af_inet.c
> > > +++ b/net/ipv4/af_inet.c
> > > @@ -198,6 +198,9 @@ int inet_listen(struct socket *sock, int backlog)
> > >  	unsigned char old_state;
> > >  	int err;
> > >  
> > > +	if (backlog >= (1 << 16))
> > > +		return EINVAL;
> > > +
> > >  	lock_sock(sk);
> > >  
> > >  	err = -EINVAL;
> > 
> > This seems pretty buggy to me.
> > 
> > 1) EINVAL is not -EINVAL
> > 
> > 2) This might break existing applications.
> 
> Yes, we should clamp the value to netdev_max_backlog.

Nonsense, somaxconn would make more sense.

Sorry,

  Hannes

Re: [PATCH] net: Check the argument for listen(2)

[Eric Dumazet]

On Fri, 2013-06-28 at 18:34 +0200, Hannes Frederic Sowa wrote:

> Nonsense, somaxconn would make more sense.
> 


If we keep u16, we could limit the sysctl (somaxconn,
tcp_max_syn_backlog) limits to 65535

Re: [PATCH] net: Check the argument for listen(2)

[Stephen Hemminger]

On Sat, 29 Jun 2013 00:14:36 +0800
Changli Gao <xiaosuo@gmail.com> wrote:

> As we use u16 to save the value of the argument for listen(2),
> we'd better check if the value is larger than SINT_MAX other
> than cut it down silently on error.
> ---
>  net/ipv4/af_inet.c |    3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/net/ipv4/af_inet.c b/net/ipv4/af_inet.c
> index b4d0be2..35aaf00 100644
> --- a/net/ipv4/af_inet.c
> +++ b/net/ipv4/af_inet.c
> @@ -198,6 +198,9 @@ int inet_listen(struct socket *sock, int backlog)
>  	unsigned char old_state;
>  	int err;
>  
> +	if (backlog >= (1 << 16))
> +		return EINVAL;
> +
>  	lock_sock(sk);
>  
>  	err = -EINVAL;

Is this just a theoretical problem or is there an example?
Since this is a user API, you should check related standards, it maybe
that the kernel should just silently truncate. Returning errors
to legacy applications makes people really angry.

If you decide that returning an error is the correct behaviour
then the return value should be negative in order to follow kernel practice
and other parts of same code.

Rather than open coding >= (1<<16) might be better to > USHRT_MAX.

Lastly, a test like this deserves a comment like:
       /* since sk_max_ack_backlog is ushort */