Re: [PATCH] netfilter: nfnetlink: fix uninitialized local variable

[Pablo Neira Ayuso <pablo@netfilter.org>]

For the record:

https://git.kernel.org/pub/scm/linux/kernel/git/netfilter/nf.git/commit/?id=d1a7b382a9d3f0f3e5a80e0be2991c075fa4f618

Fixes: bf2ac490d28c ("netfilter: nfnetlink: Handle ACK flags for batch messages")

On Thu, Aug 15, 2024 at 10:32:11AM +0200, Pablo Neira Ayuso wrote:
> There is a fix already traveling for this in a pull request.
> 
> On Thu, Aug 15, 2024 at 04:27:33PM +0800, icejl wrote:
> > In the nfnetlink_rcv_batch function, an uninitialized local variable
> > extack is used, which results in using random stack data as a pointer.
> > This pointer is then used to access the data it points to and return
> > it as the request status, leading to an information leak. If the stack
> > data happens to be an invalid pointer, it can cause a pointer access
> > exception, triggering a kernel crash.
> > 
> > Signed-off-by: icejl <icejl0001@gmail.com>
> > ---
> >  net/netfilter/nfnetlink.c | 1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff --git a/net/netfilter/nfnetlink.c b/net/netfilter/nfnetlink.c
> > index 4abf660c7baf..b29b281f4b2c 100644
> > --- a/net/netfilter/nfnetlink.c
> > +++ b/net/netfilter/nfnetlink.c
> > @@ -427,6 +427,7 @@ static void nfnetlink_rcv_batch(struct sk_buff *skb, struct nlmsghdr *nlh,
> >  
> >  	nfnl_unlock(subsys_id);
> >  
> > +	memset(&extack, 0, sizeof(extack));
> >  	if (nlh->nlmsg_flags & NLM_F_ACK)
> >  		nfnl_err_add(&err_list, nlh, 0, &extack);
> >  
> > -- 
> > 2.34.1
> >