linux-kernel - Re: [PATCH] Prevent out-of-bounds read/write in bcmasp_netfilt_rd and bcmasp_netfilt

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Date:   Fri, 3 Nov 2023 19:33:34 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Justin Chen <justin.chen@...adcom.com>
Cc:     Yuran Pereira <yuran.pereira@...mail.com>, davem@...emloft.net,
        netdev@...r.kernel.org, florian.fainelli@...adcom.com,
        linux-kernel@...r.kernel.org, edumazet@...gle.com,
        bcm-kernel-feedback-list@...adcom.com, kuba@...nel.org,
        pabeni@...hat.com, linux-kernel-mentees@...ts.linuxfoundation.org
Subject: Re: [PATCH] Prevent out-of-bounds read/write in bcmasp_netfilt_rd
 and bcmasp_netfilt_wr

On Fri, Nov 03, 2023 at 11:23:16AM -0700, Justin Chen wrote:
> 
> 
> On 11/3/23 5:57 AM, Greg KH wrote:
> > On Fri, Nov 03, 2023 at 05:57:48PM +0530, Yuran Pereira wrote:
> > > The functions `bcmasp_netfilt_rd` and `bcmasp_netfilt_wr` both call
> > > `bcmasp_netfilt_get_reg_offset` which, when it fails, returns `-EINVAL`.
> > > This could lead to an out-of-bounds read or write when `rx_filter_core_rl`
> > > or `rx_filter_core_wl` is called.
> > > 
> > > This patch adds a check in both functions to return immediately if
> > > `bcmasp_netfilt_get_reg_offset` fails. This prevents potential out-of-bounds read
> > > or writes, and ensures that no undefined or buggy behavior would originate from
> > > the failure of `bcmasp_netfilt_get_reg_offset`.
> > > 
> > > Addresses-Coverity-IDs: 1544536 ("Out-of-bounds access")
> > > Signed-off-by: Yuran Pereira <yuran.pereira@...mail.com>
> > > ---
> > >   drivers/net/ethernet/broadcom/asp2/bcmasp.c | 4 ++++
> > >   1 file changed, 4 insertions(+)
> > > 
> > > diff --git a/drivers/net/ethernet/broadcom/asp2/bcmasp.c b/drivers/net/ethernet/broadcom/asp2/bcmasp.c
> > > index 29b04a274d07..8b90b761bdec 100644
> > > --- a/drivers/net/ethernet/broadcom/asp2/bcmasp.c
> > > +++ b/drivers/net/ethernet/broadcom/asp2/bcmasp.c
> > > @@ -227,6 +227,8 @@ static void bcmasp_netfilt_wr(struct bcmasp_priv *priv,
> > >   	reg_offset = bcmasp_netfilt_get_reg_offset(priv, nfilt, reg_type,
> > >   						   offset);
> > > +	if (reg_offset < 0)
> > > +		return;
> > >   	rx_filter_core_wl(priv, val, reg_offset);
> > >   }
> > > @@ -244,6 +246,8 @@ static u32 bcmasp_netfilt_rd(struct bcmasp_priv *priv,
> > >   	reg_offset = bcmasp_netfilt_get_reg_offset(priv, nfilt, reg_type,
> > >   						   offset);
> > > +	if (reg_offset < 0)
> > > +		return 0;
> > 
> > Shouldn't you return an error here?
> > 
> > thanks
> > 
> > greg k-h
> 
> As long as offset is less than MAX_WAKE_FILTER_SIZE we don't need to worry
> about error checking. This is already checked before we call
> netfilt_get_reg_offset() in both cases. Instead of returning -EINVAL in
> neffilt_get_reg_offset() lets return 0. This will silence the coverity
> check. In practice we will never hit this logic.

Then don't change it, coverity is incorrect here.

greg k-h