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

[Pablo Neira Ayuso]

On Thu, Aug 15, 2024 at 02:04:04AM -0700, Breno Leitao wrote:
> 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@xxxxxxxxx>
> > ---
> >  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);
> 
> There is a memset later in that function , inside the 
> `while (skb->len >= nlmsg_total_size(0))` loop. Should that one be
> removed?

no, the batch contains a series of netlink message, each of them needs
a fresh extack area which is zeroed.

this pointer leak only affects the recently released 6.10, older
kernels are not affected.