Re: [Security] [PATCH] xtensa: prevent arbitrary read in ptrace

[Oleg Nesterov <oleg@redhat.com>]

On 07/08, Andrew Morton wrote:
>
> On Thu, 07 Jul 2011 20:03:54 -0400
> Dan Rosenberg <drosenberg@vsecurity.com> wrote:
>
> > Prevent an arbitrary kernel read. Check the user pointer with
> > access_ok() before copying data in.
> >
> > Signed-off-by: Dan Rosenberg <drosenberg@vsecurity.com>
> > Cc: stable@kernel.org
> > ---
> >  arch/xtensa/kernel/ptrace.c |    3 +++
> >  1 files changed, 3 insertions(+), 0 deletions(-)
> > 
> > diff --git a/arch/xtensa/kernel/ptrace.c b/arch/xtensa/kernel/ptrace.c
> > index c72c947..ddce75e 100644
> > --- a/arch/xtensa/kernel/ptrace.c
> > +++ b/arch/xtensa/kernel/ptrace.c
> > @@ -147,6 +147,9 @@ int ptrace_setxregs(struct task_struct *child, void __user *uregs)
> >  	elf_xtregs_t *xtregs = uregs;
> >  	int ret = 0;
> >
> > +	if (!access_ok(VERIFY_READ, uregs, sizeof(elf_xtregs_t)))
> > +		return -EIO;
>
> This should be -EFAULT, methinks?

Also, it seems that ptrace_setxregs/ptrace_getxregs could be static?

The patch looks "obviously correct" but I don't understand this code.

Hmm. We don't read/write the XTENSA_HAVE_COPROCESSORS data, but use
sizeof(elf_xtregs_t) anyway. This looks a bit strange but I guess
this doesn't matter.

Oleg.