From mboxrd@z Thu Jan 1 00:00:00 1970 From: Aleksa Sarai Subject: Re: [PATCH v12 01/12] lib: introduce copy_struct_{to,from}_user helpers Date: Thu, 5 Sep 2019 23:40:17 +1000 Message-ID: <20190905134017.rstiqa6v6roslzlu@yavin.dot.cyphar.com> References: <20190904201933.10736-1-cyphar@cyphar.com> <20190904201933.10736-2-cyphar@cyphar.com> <20190905110544.d6c5t7rx25kvywmi@wittgenstein> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="lfmn5rszd42a2efo" Return-path: Content-Disposition: inline In-Reply-To: <20190905110544.d6c5t7rx25kvywmi@wittgenstein> Sender: linux-kernel-owner@vger.kernel.org To: Christian Brauner Cc: Al Viro , Jeff Layton , "J. Bruce Fields" , Arnd Bergmann , David Howells , Shuah Khan , Shuah Khan , Ingo Molnar , Peter Zijlstra , Christian Brauner , Rasmus Villemoes , Eric Biederman , Andy Lutomirski , Andrew Morton , Alexei Starovoitov , Kees Cook , Jann Horn , Tycho Andersen , David Drysdale , Chanho Min , Oleg List-Id: linux-api@vger.kernel.org --lfmn5rszd42a2efo Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On 2019-09-05, Christian Brauner wrote: > On Thu, Sep 05, 2019 at 06:19:22AM +1000, Aleksa Sarai wrote: > > A common pattern for syscall extensions is increasing the size of a > > struct passed from userspace, such that the zero-value of the new fields > > result in the old kernel behaviour (allowing for a mix of userspace and > > kernel vintages to operate on one another in most cases). This is done > > in both directions -- hence two helpers -- though it's more common to > > have to copy user space structs into kernel space. > >=20 > > Previously there was no common lib/ function that implemented > > the necessary extension-checking semantics (and different syscalls > > implemented them slightly differently or incompletely[1]). A future > > patch replaces all of the common uses of this pattern to use the new > > copy_struct_{to,from}_user() helpers. > >=20 > > [1]: For instance {sched_setattr,perf_event_open,clone3}(2) all do do > > similar checks to copy_struct_from_user() while rt_sigprocmask(2) > > always rejects differently-sized struct arguments. > >=20 > > Suggested-by: Rasmus Villemoes > > Signed-off-by: Aleksa Sarai [...] > > + if (unlikely(!access_ok(src, usize))) > > + return -EFAULT; > > + > > + /* Deal with trailing bytes. */ > > + if (usize < ksize) > > + memset(dst + size, 0, rest); [...] > That's a change in behavior for clone3() and sched at least, no? Unless > - which I guess you might have done - you have moved the "error out when > the struct is too small" part before the call to copy_struct_from_user() > for them. Yes, I've put the minimum size check to the callers in all of the cases (in the case of clone3() I've #define'd a CLONE_ARGS_SIZE_VER0 to match the others -- see patch 2 of the series). --=20 Aleksa Sarai Senior Software Engineer (Containers) SUSE Linux GmbH --lfmn5rszd42a2efo Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- iHUEABYIAB0WIQSxZm6dtfE8gxLLfYqdlLljIbnQEgUCXXEQPQAKCRCdlLljIbnQ EmI0AQDWLDq3CfEAPKhr2gyUgsbcgKNMnsXSA4qFj1Jjd61fzQEAqPhisgSoisGO mIYO56C9d94ktWhTGVP9Bs10TG3V/Ac= =1PLZ -----END PGP SIGNATURE----- --lfmn5rszd42a2efo--