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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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