Messages in this thread | | | Date | Sat, 26 Feb 2011 13:35:22 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH 0/4 RESEND] exec: unify compat/non-compat code |
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On 02/25, Linus Torvalds wrote: > > On Fri, Feb 25, 2011 at 9:52 AM, Oleg Nesterov <oleg@redhat.com> wrote: > >> On 12/01, Milton Miller wrote: > >> > > >> > > +#ifdef CONFIG_COMPAT > >> > > +int compat_do_execve(char * filename, > >> > > + compat_uptr_t __user *argv, > >> > > + compat_uptr_t __user *envp, > >> > > + struct pt_regs * regs) > >> > > +{ > >> > > + return do_execve_common(filename, > >> > > + (void __user*)argv, (void __user*)envp, > >> > > >> > Shouldn't these be compat_ptr(argv)? (makes a difference on s390) > > Indeed. The "compat_uptr_t __user *argv" is wrong, and it should be just > > compat_uptr_t argv; > > and then every time you turn it into a pointer, it should use > "compat_ptr(argv)".
Oh, perhaps, and I was thinking about this too. But this is another issue, no? Or I misunderstood.
First of all, I agree that perhaps it makes sense to change the signature of compat_do_execve()
- compat_do_execve(compat_uptr_t __user *argv) + compat_do_execve(compat_uptr_t argv)
but this has nothing to do with this series. We can do this before or after ("after" seems simpler").
> - user passes "compat_uptr_t"
Yes,
> - the kernel can turn that into "compat_uptr_t __user *" by doing > > compat_uptr_t __user *pptr; > pptr = compat_ptr(argv);
Yes! and the kernel already does this before it calls compat_do_execve(), iow compat_do_execve() gets the result of compat_ptr(compat_ptr_from_user).
> - the kernel needs to fetch the individual entries with > > compat_uptr_t cuptr = get_user(pptr); > > - the kernel can then turn _those_ into the actual pointers to the string with > > const char __user *str = compat_ptr(cuptr);
Yes, and this is exactly what get_arg_ptr(compat => true) does.
> > So, once again, this should not (and can not) be compat_ptr(argv) afaics. > > It can be, and probably should.
Only if we change the signature of compat_do_execve(). With the current code yet another compat_ptr() is not needed and it is simply wrong, this is what I meant when I replied to Milton.
> But the low-level s390 wrapper > function may have done one of the levels already. It probably > shouldn't, and we _should_ do the "compat_ptr()" thing a the generic C > level.
Agreed, but currently this compat_ptr() thing belongs to the caller.
IOW. Lets look at the current code. arch/ calls compat_do_execve(compat_uptr_t __user *argv)->compat_count(argv) which does get_user(argv) without any conversion, because argv was already converted or arch/ is buggy.
Both do_execve() and compat_do_execve() accept the valid pointer which does not need any conversion. But this pointer points to different things, either to "char*" of "compat_uptr_t".
However, please see my reply to 2-3/5, I agree that this is confusing and can be cleanuped.
Or do you think I missed something else?
Oleg.
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