linux-kernel - Re: [PATCH 4.19 233/422] netfilter: nf_tables: avoid BUG

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Message-ID: <20191121202514.GA812833@kroah.com>
Date:   Thu, 21 Nov 2019 21:25:14 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Pavel Machek <pavel@...x.de>
Cc:     linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Florian Westphal <fw@...len.de>,
        Pablo Neira Ayuso <pablo@...filter.org>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.19 233/422] netfilter: nf_tables: avoid BUG_ON usage

On Thu, Nov 21, 2019 at 09:16:18PM +0100, Pavel Machek wrote:
> Hi!
> 
> > From: Florian Westphal <fw@...len.de>
> > 
> > [ Upstream commit fa5950e498e7face21a1761f327e6c1152f778c3 ]
> > 
> > None of these spots really needs to crash the kernel.
> > In one two cases we can jsut report error to userspace, in the other
> > cases we can just use WARN_ON (and leak memory instead).
> 
> Do these conditions trigger for someone, to warrant -stable patch?
> 
> > +++ b/net/netfilter/nft_cmp.c
> > @@ -79,7 +79,8 @@ static int nft_cmp_init(const struct nft_ctx *ctx, const struct nft_expr *expr,
> >  
> >  	err = nft_data_init(NULL, &priv->data, sizeof(priv->data), &desc,
> >  			    tb[NFTA_CMP_DATA]);
> > -	BUG_ON(err < 0);
> > +	if (err < 0)
> > +		return err;
> >  
> >  	priv->sreg = nft_parse_register(tb[NFTA_CMP_SREG]);
> >  	err = nft_validate_register_load(priv->sreg, desc.len);
> > @@ -129,7 +130,8 @@ static int nft_cmp_fast_init(const struct nft_ctx *ctx,
> >  
> >  	err = nft_data_init(NULL, &data, sizeof(data), &desc,
> >  			    tb[NFTA_CMP_DATA]);
> > -	BUG_ON(err < 0);
> > +	if (err < 0)
> > +		return err;
> >  
> >  	priv->sreg = nft_parse_register(tb[NFTA_CMP_SREG]);
> >  	err = nft_validate_register_load(priv->sreg, desc.len);
> 
> This goes from "kill kernel with backtrace" to "silently return
> failure". Should WARN_ON() be preserved here?

if this can be triggered, then the people running with panic-on-warn
would reboot.  It's best to handle it properly here.  And it isn't
"silent", the error is returned.

thanks,

greg k-h