2009-07-21 16:53:15

by Lennart Poettering

Subject: Can access to /proc/$PID/exe be relaxed?

Hi!

Unless I am mistaken a process currently needs CAP_SYS_PTRACE to read
/proc/$PID/exe for abritrary processes. Does that make sense? Could
that be relaxed? Is there any reason to limit access to that link at
all? To me the data from /proc/$PID/cmdline seems to be far more
worthy to be protected than /proc/$PID/exe, or am I missing something?

Tbh, looking at the code I don't really get where CAP_SYS_PTRACE seems
to be required, but experimenting from userspace this seems to be the
case.

Lennart

--
Lennart Poettering Red Hat, Inc.
lennart [at] poettering [dot] net
http://0pointer.net/lennart/ GnuPG 0x1A015CC4

2009-07-21 17:06:43

by Denys Vlasenko

Subject: Re: Can access to /proc/$PID/exe be relaxed?

On Tue, Jul 21, 2009 at 6:52 PM, Lennart Poettering<[email protected]> wrote:
> Hi!
>
> Unless I am mistaken a process currently needs CAP_SYS_PTRACE to read
> /proc/$PID/exe for abritrary processes.

You mean "readlink'?

> Does that make sense? Could
> that be relaxed? Is there any reason to limit access to that link at
> all? To me the data from /proc/$PID/cmdline seems to be far more
> worthy to be protected than /proc/$PID/exe, or am I missing something?
>
> Tbh, looking at the code I don't really get where CAP_SYS_PTRACE seems
> to be required, but experimenting from userspace this seems to be the
> case.

Another annoying thing is that sometimes processes cannot open
their own /proc/self/fd/N. Example:

# setuidgid 200:200 cat /proc/self/fd/0
cat: /proc/self/fd/0: Permission denied

In real life this happened when I wanted to redirect apache's
log to stderr. The config directive only allowed redirecting
to a file, so I specified /proc/self/fd/2. It does not work
if apache drops root after startup.

--
vda

2009-07-21 17:18:08

by Lennart Poettering

Subject: Re: Can access to /proc/$PID/exe be relaxed?

On Tue, 21.07.09 19:06, Denys Vlasenko ([email protected]) wrote:

>
> On Tue, Jul 21, 2009 at 6:52 PM, Lennart Poettering<[email protected]> wrote:
> > Hi!
> >
> > Unless I am mistaken a process currently needs CAP_SYS_PTRACE to read
> > /proc/$PID/exe for abritrary processes.
>
> You mean "readlink'?

Yes.

Lennart

--
Lennart Poettering Red Hat, Inc.
lennart [at] poettering [dot] net
http://0pointer.net/lennart/ GnuPG 0x1A015CC4