Date: Sun, 29 Jan 2012 17:39:04 -0500 From: David Schultz <das@FreeBSD.ORG> To: Kostik Belousov <kostikbel@gmail.com> Cc: svn-src-head@FreeBSD.ORG, svn-src-all@FreeBSD.ORG, Gleb Smirnoff <glebius@FreeBSD.ORG>, src-committers@FreeBSD.ORG, Bruce Evans <brde@optusnet.com.au> Subject: Re: svn commit: r230583 - head/sys/kern Message-ID: <20120129223904.GA37483@zim.MIT.EDU> In-Reply-To: <20120129062327.GK2726@deviant.kiev.zoral.com.ua> References: <201201261159.q0QBxma2086162@svn.freebsd.org> <20120126233110.C960@besplex.bde.org> <20120126153641.GA68112@FreeBSD.org> <20120127194612.H1547@besplex.bde.org> <20120127091244.GZ2726@deviant.kiev.zoral.com.ua> <20120127194221.GA25723@zim.MIT.EDU> <20120128123748.GD2726@deviant.kiev.zoral.com.ua> <20120129001225.GA32220@zim.MIT.EDU> <20120129062327.GK2726@deviant.kiev.zoral.com.ua>
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On Sun, Jan 29, 2012, Kostik Belousov wrote:
> On Sat, Jan 28, 2012 at 07:12:25PM -0500, David Schultz wrote:
> > On Sat, Jan 28, 2012, Kostik Belousov wrote:
> > > On Fri, Jan 27, 2012 at 02:42:21PM -0500, David Schultz wrote:
> > > > On Fri, Jan 27, 2012, Kostik Belousov wrote:
> > > > > On Fri, Jan 27, 2012 at 07:50:30PM +1100, Bruce Evans wrote:
> > > > > > On Thu, 26 Jan 2012, Gleb Smirnoff wrote:
> > > > > >
> > > > > > >On Thu, Jan 26, 2012 at 11:53:57PM +1100, Bruce Evans wrote:
> > > > > > >B> > @@ -1552,6 +1552,12 @@ aio_aqueue(struct thread *td, struct aio
> > > > > > >B> > return (error);
> > > > > > >B> > }
> > > > > > >B> >
> > > > > > >B> > + /* XXX: aio_nbytes is later casted to signed types. */
> > > > > > >B> > + if ((int)aiocbe->uaiocb.aio_nbytes < 0) {
> > > > > > >B>
> > > > > > >B> This should avoid implementation-defined behaviour by checking if
> > > > > > >B>
> > > > > > >B> (uncast)aiocbe->uaiocb.aio_nbytes > INT_MAX.
> > > > > >
> > > > > > >Is the attached patch okay?
> > > > > >
> > > > > > Yes. It now matches the style used for read^Wsys_read() and friends.
> > > > > > This used to have to fit the count in "int uio_resid". uio_resid now
> > > > > > has type ssize_t, but for some reason the old INT_MAX limits remain.
> > > > >
> > > > > Well, I can revive the patch. I still think it is good to get rid of
> > > > > the limit.
> > > >
> > > > The correct limit on the maximum size of a single read/write is
> > > > SSIZE_MAX, but FreeBSD uses INT_MAX. It's not safe to raise the
> > > > limit yet, though, because of bugs in several filesystems. For
> > > > example, FFS copies uio_resid into a local variable of type int.
> > > > I have some old patches that fix some of these issues for FFS and
> > > > cd9660, but surely there are more places I didn't notice.
> > > >
> > > Absolutely agree.
> > >
> > > http://people.freebsd.org/~kib/misc/uio_resid.5.patch
> >
> > Nice. You found a lot more than I've got in my tree, and you even
> > fixed the return values. There are at least a few more places to
> > fix. For instance, cd9660 and the NFS client pass uio_resid or
> > iov_len to min(), which operates on ints. (Incidentally, C11
> > generics ought to make it possible to write type-generic min()
> > and max() functions.)
>
> Thank you, http://people.freebsd.org/~kib/misc/uio_resid.6.patch
> changed them to MIN().
This looks good to me. I tried to think of other places that you
might have missed, and the only one that occurred to me is the
pipe code. sys_pipe.c has an `int orig_resid' and lots of bogus
casts of iov_len and uio_resid to type u_int. Some look harmless,
although it appears that writing a multiple of 2^32 bytes might
result in pipe_build_write_buffer() allocating a 0-length buffer.
My only reservation is that raising the limit could unmask a
kernel buffer overflow if we missed something, but I guess we have
to cross that bridge some day anyway.
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