From: Jakub Kicinski <kuba@kernel.org>
To: Kees Cook <keescook@chromium.org>
Cc: kernel test robot <lkp@intel.com>,
"David S. Miller" <davem@davemloft.net>,
Eric Dumazet <edumazet@google.com>,
Paolo Abeni <pabeni@redhat.com>,
Johannes Berg <johannes@sipsolutions.net>,
Jeff Johnson <quic_jjohnson@quicinc.com>,
Michael Walle <mwalle@kernel.org>,
Max Schulze <max.schulze@online.de>,
netdev@vger.kernel.org, linux-wireless@vger.kernel.org,
linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org
Subject: Re: [PATCH] netlink: Return unsigned value for nla_len()
Date: Thu, 30 Nov 2023 17:25:20 -0800 [thread overview]
Message-ID: <20231130172520.5a56ae50@kernel.org> (raw)
In-Reply-To: <20231130200058.work.520-kees@kernel.org>
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
next prev parent reply other threads:[~2023-12-01 1:25 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-11-30 20:01 [PATCH] netlink: Return unsigned value for nla_len() Kees Cook
2023-11-30 20:11 ` Gustavo A. R. Silva
2023-12-01 1:25 ` Jakub Kicinski [this message]
2023-12-01 7:45 ` Johannes Berg
2023-12-01 18:17 ` Kees Cook
2023-12-01 18:45 ` Jakub Kicinski
2023-12-02 4:39 ` Kees Cook
2023-12-02 5:16 ` Jakub Kicinski
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