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
