Re: [PATCH v2 0/9] procfs: protect /proc//* files with file->f_cred

Djalal Harouni
2013-10-02T14:38:07Z

On Tue, Oct 01, 2013 at 06:40:41PM -0700, Andy Lutomirski wrote:
> On 10/01/2013 01:26 PM, Djalal Harouni wrote:
> > /proc/<pid>/* entries varies at runtime, appropriate permission checks
> > need to happen during each system call.
> >
> > Currently some of these sensitive entries are protected by performing
> > the ptrace_may_access() check. However even with that the /proc file
> > descriptors can be passed to a more privileged process
> > (e.g. a suid-exec) which will pass the classic ptrace_may_access()
> > check. In general the ->open() call will be issued by an unprivileged
> > process while the ->read(),->write() calls by a more privileged one.
> >
> > Example of these files are:
> > /proc/*/syscall, /proc/*/stack etc.
> >
> > And any open(/proc/self/*) then suid-exec to read()/write() /proc/self/*
> >
> >
> > These files are protected during read() by the ptrace_may_access(),
> > however the file descriptor can be passed to a suid-exec which can be
> > used to read data and bypass ASLR. Of course this was discussed several
> > times on LKML.
>
> Can you elaborate on what it is that you're fixing? That is, can you
> give a concrete example of what process opens what file and passes the
> fd to what process?
Yes, the references were already given in this email:
https://lkml.org/lkml/2013/8/31/209

This has been discussed several times on lkml:
https://lkml.org/lkml/2013/8/28/544

https://lkml.org/lkml/2013/8/28/564 (check Kees's references)

> I'm having trouble following your description.
Process open a /proc file and pass the fd to a more privilaged process
that will pass the ptrace_may_access() check, while the original process
that opened that file should fail at the ptrace_may_access()

> --Andy
>

--
Djalal Harouni