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SubjectRe: [RFC] c/r: prctl: Add ability to set new mm_struct::exe_file v3
On Wed, Mar 14, 2012 at 09:47:28AM +0400, Cyrill Gorcunov wrote:
> On Tue, Mar 13, 2012 at 06:41:06PM -0700, Matt Helsley wrote:
> ...
> > > +
> > > + exe_file = fget(fd);
> > > + if (!exe_file)
> > > + return -EBADF;
> > > +
> > > + dentry = exe_file->f_path.dentry;
> > > +
> > > + /*
> > > + * Because the original mm->exe_file
> > > + * points to executable file, make sure
> > > + * this one is executable as well to not
> > > + * break an overall picture.
> > > + */
> > > + err = -EACCES;
> > > + if (!S_ISREG(dentry->d_inode->i_mode) ||
> > > + exe_file->f_path.mnt->mnt_flags & MNT_NOEXEC)
> > > + goto exit;
> >
> > You could factor out this portion of the access checking from open_exec()
> > after the do_filp_open() in open_exec() and re-use it here. I know it's
> > tiny helper but tying these two together might be good for
> > maintenance later.
> >
>
> Matt, I really dont wanna touch code outside of prctl and this function
> in particualar, at least in this patch, ie I can clean up and factor out
> is on top of the patch, as a separate task.

OK, sounds fine.

>
> > Should it check for some of the flags open_exec() uses? open_exec()
> > passes:
> >
> > O_LARGEFILE|O_RDONLY|__FMODE_EXEC
> >
> > to do_filp_open(). I think a O_RDONLY check might be good. I don't
> > think __FMODE_EXEC is something userspace can set so could be ignored.
> > O_LARGEFILE might be important though.
>
> Well, we're not going to read from this file, so it is not that important
> at moment, so previously I've had
>
> > + if ((exe_file->f_flags & O_ACCMODE) != O_RDONLY)
> > + goto exit;
>
> and Oleg pointed me
>
> | But the O_RDONLY check looks strange. We are not going to write
> | to this file, we only set the name (and that is why I think it
> | should be mm->exe_path). What is the point to check that the file
> | was opened without FMODE_WRITE? Even if there were any security
> | risk the apllication can open this file again with the different
> | flags.
>
> so I dropped it. And I think the same applies to O_LARGEFILE. Sure
> it's not a problem to bring it back but should we?

OK, sorry I must have missed that portion of the discussion. It all looks
good to me.

Cheers,
-Matt



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