netdev - Re: ethtool generate a buffer overflow in strlen

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Date:   Fri, 22 Jul 2022 14:29:42 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Jules Maselbas <jmaselbas@...ray.eu>
Cc:     Claudiu Manoil <claudiu.manoil@....com>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: ethtool generate a buffer overflow in strlen

On Fri, 22 Jul 2022 19:37:46 +0200 Jules Maselbas wrote:
> There is suspicious lines in the file drivers/net/ethernet/freescale/enetc/enetc_ethtool.c:
>    { ENETC_PM0_R1523X, "MAC rx 1523 to max-octet packets" },
> and:
>    { ENETC_PM0_T1523X, "MAC tx 1523 to max-octet packets" },
> 
> Where the string length is actually greater than 32 bytes which is more
> than the reserved space for the name. This structure is defined as
> follow:
>     static const struct {
>         int reg;
>         char name[ETH_GSTRING_LEN];
>     } enetc_port_counters[] = { ...
> 
> In the function enetc_get_strings(), there is a strlcpy call on the
> counters names which in turns calls strlen on the src string, causing
> an out-of-bound read, at least out-of the string.
> 
> I am not sure that's what caused the BUG, as I don't really know how
> fortify works but I thinks this might only be visible when fortify is
> enabled.
> 
> I am not sure on how to fix this issue, maybe use `char *` instead of
> an byte array.

Thanks for the report!

I'd suggest to just delete the RMON stats in the unstructured API
in this driver and report them via
 
	ethtool -S eth0 --groups rmon

No point trying to figure out a way to make the old API more
resilient IMO when we have an alternative.