Re: [PATCH] ipv6_sockglue: Fix a missing-check bug in ip6_ra_control()

[Gen Zhang <blackgod016574@gmail.com>]

On Mon, Jul 01, 2019 at 10:57:36AM +0200, Jiri Slaby wrote:
> On 24. 05. 19, 5:19, Gen Zhang wrote:
> > In function ip6_ra_control(), the pointer new_ra is allocated a memory 
> > space via kmalloc(). And it is used in the following codes. However, 
> > when there is a memory allocation error, kmalloc() fails. Thus null 
> > pointer dereference may happen. And it will cause the kernel to crash. 
> > Therefore, we should check the return value and handle the error.
> > 
> > Signed-off-by: Gen Zhang <blackgod016574@gmail.com>
> > 
> > ---
> > diff --git a/net/ipv6/ipv6_sockglue.c b/net/ipv6/ipv6_sockglue.c
> > index 40f21fe..0a3d035 100644
> > --- a/net/ipv6/ipv6_sockglue.c
> > +++ b/net/ipv6/ipv6_sockglue.c
> > @@ -68,6 +68,8 @@ int ip6_ra_control(struct sock *sk, int sel)
> >  		return -ENOPROTOOPT;
> >  
> >  	new_ra = (sel >= 0) ? kmalloc(sizeof(*new_ra), GFP_KERNEL) : NULL;
> > +	if (sel >= 0 && !new_ra)
> > +		return -ENOMEM;
> >  
> >  	write_lock_bh(&ip6_ra_lock);
> >  	for (rap = &ip6_ra_chain; (ra = *rap) != NULL; rap = &ra->next) {
> > 
> 
> Was this really an omission? There is (!new_ra) handling below the for loop:
>         if (!new_ra) {
>                 write_unlock_bh(&ip6_ra_lock);
>                 return -ENOBUFS;
>         }
> 
> It used to handle both (sel >= 0) and (sel == 0) cases and it used to
> return ENOBUFS in case of failure. For (sel >= 0) it also could at least
> return EADDRINUSE when a collision was found -- even if memory was
> exhausted.
> 
> In anyway, how could this lead to a pointer dereference? And why/how did
> this get a CVE number?
> 
> thanks,
> -- 
> js
> suse labs
This CVE is already disputed by other maintainers and marked *DISPUTED*
on the website.

Thanks
Gen