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Message-ID: <20231130172520.5a56ae50@kernel.org> Date: Thu, 30 Nov 2023 17:25:20 -0800 From: Jakub Kicinski <kuba@...nel.org> To: Kees Cook <keescook@...omium.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 Thu, 30 Nov 2023 12:01:01 -0800 Kees Cook wrote: > 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). As Johannes predicted I'd rather not :( The callers should put the nlattr thru nla_ok() during validation (nla_validate()), or walking (nla_for_each_* call nla_ok()). > -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; > } Note the the NLA_HDRLEN is the length of struct nlattr. I mean of the @nla object that gets passed in as argument here. So accepting that nla->nla_len may be < NLA_HDRLEN means that we are okay with dereferencing a truncated object... We can consider making the return unsinged without the condition maybe? -- pw-bot: cr
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