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Message-ID: <31934933-24cf-42bf-90d1-c83b44b71d4f@embeddedor.com>
Date: Thu, 30 Nov 2023 14:11:25 -0600
From: "Gustavo A. R. Silva" <gustavo@...eddedor.com>
To: Kees Cook <keescook@...omium.org>, Jakub Kicinski <kuba@...nel.org>
Cc: kernel test robot <lkp@...el.com>, "David S. Miller"
<davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
Paolo Abeni <pabeni@...hat.com>, Johannes Berg <johannes@...solutions.net>,
Jeff Johnson <quic_jjohnson@...cinc.com>, Michael Walle <mwalle@...nel.org>,
Max Schulze <max.schulze@...ine.de>, netdev@...r.kernel.org,
linux-wireless@...r.kernel.org, linux-kernel@...r.kernel.org,
linux-hardening@...r.kernel.org
Subject: Re: [PATCH] netlink: Return unsigned value for nla_len()
On 11/30/23 14:01, Kees Cook wrote:
> The return value from nla_len() is never expected to be negative, and can
> never be more than struct nlattr::nla_len (a u16). Adjust the prototype
> on the function, and explicitly bounds check the subtraction. This will
> let GCC's value range optimization passes know that the return can never
> be negative, and can never be larger than u16. As recently discussed[1],
> this silences the following warning in GCC 12+:
>
> net/wireless/nl80211.c: In function 'nl80211_set_cqm_rssi.isra':
> net/wireless/nl80211.c:12892:17: warning: 'memcpy' specified bound 18446744073709551615 exceeds maximum object size 9223372036854775807 [-Wstringop-overflow=]
> 12892 | memcpy(cqm_config->rssi_thresholds, thresholds,
> | ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 12893 | flex_array_size(cqm_config, rssi_thresholds,
> | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 12894 | n_thresholds));
> | ~~~~~~~~~~~~~~
>
> This has the additional benefit of being defensive in the face of nlattr
> corruption or logic errors (i.e. nla_len being set smaller than
> NLA_HDRLEN).
>
> Reported-by: kernel test robot <lkp@...el.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202311090752.hWcJWAHL-lkp@intel.com/ [1]
> Cc: Jakub Kicinski <kuba@...nel.org>
> Cc: "David S. Miller" <davem@...emloft.net>
> Cc: Eric Dumazet <edumazet@...gle.com>
> Cc: Paolo Abeni <pabeni@...hat.com>
> Cc: Johannes Berg <johannes@...solutions.net>
> Cc: Jeff Johnson <quic_jjohnson@...cinc.com>
> Cc: Michael Walle <mwalle@...nel.org>
> Cc: Max Schulze <max.schulze@...ine.de>
> Cc: netdev@...r.kernel.org
> Cc: linux-wireless@...r.kernel.org
> Signed-off-by: Kees Cook <keescook@...omium.org>
Looks good to me.
Reviewed-by: Gustavo A. R. Silva <gustavoars@...nel.org>
Thanks
--
Gustavo
> ---
> include/net/netlink.h | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/include/net/netlink.h b/include/net/netlink.h
> index 167b91348e57..c59679524705 100644
> --- a/include/net/netlink.h
> +++ b/include/net/netlink.h
> @@ -1214,9 +1214,9 @@ static inline void *nla_data(const struct nlattr *nla)
> * nla_len - length of payload
> * @nla: netlink attribute
> */
> -static inline int nla_len(const struct nlattr *nla)
> +static inline u16 nla_len(const struct nlattr *nla)
> {
> - return nla->nla_len - NLA_HDRLEN;
> + return nla->nla_len > NLA_HDRLEN ? nla->nla_len - NLA_HDRLEN : 0;
> }
>
> /**
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