Re: [patch 03/26] sysfs: zero terminate sysfs write buffers (CVE-2006-1055)

[Al Viro]

On Wed, Apr 05, 2006 at 11:38:06AM -0400, Jon Smirl wrote:
> On 4/5/06, Al Viro <viro@xxxxxxxxxxxxxxxx> wrote:
> > On Wed, Apr 05, 2006 at 07:09:28PM +0400, Sergey Vlasov wrote:
> > > This will break the "color_map" sysfs file for framebuffers -
> > > drivers/video/fbsysfs.c:store_cmap() expects to get exactly 4096 bytes
> > > for a colormap with 256 entries.  In fact, the original patch which
> > > changed PAGE_SIZE - 1 to PAGE_SIZE:
> >
> > ... cheerfully assuming that nobody assumes NUL-termination and
> > everyone (sysfs patch writers!) certainly uses the length argument.
> > Fscking brilliant, that.
> >
> > Are you willing to audit all sysfs ->show() in the kernel?  Original
> > author of that turd had not been.
> >
> > FWIW, "color_map" is a blatant abuse of interface.  Doesn't get
> > any more borderline...
> 
> The firmware interface is worse. You write the ROM image line by line
> to the attribute and a hidden counter tracks how far your are into the
> image.
> 
> There needs to be a standardized way to transfer larger pieces of data
> via sysfs or we should go back to IOCTLs.

How about _NOT_ using sysfs and just having ->read()/->write() on a file in fs
of your own?  ~20 lines for all of it, not counting #include...
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