Date: Wed, 2 Oct 2013 17:51:15 +0100 From: Andy Lutomirski <luto@...capital.net> To: Djalal Harouni <tixxdz@...ndz.org> Cc: "Eric W. Biederman" <ebiederm@...ssion.com>, Kees Cook <keescook@...omium.org>, Al Viro <viro@...iv.linux.org.uk>, Andrew Morton <akpm@...ux-foundation.org>, Linus Torvalds <torvalds@...ux-foundation.org>, Ingo Molnar <mingo@...nel.org>, "Serge E. Hallyn" <serge.hallyn@...ntu.com>, Cyrill Gorcunov <gorcunov@...nvz.org>, David Rientjes <rientjes@...gle.com>, LKML <linux-kernel@...r.kernel.org>, Linux FS Devel <linux-fsdevel@...r.kernel.org>, kernel-hardening@...ts.openwall.com, Djalal Harouni <tixxdz@...il.com> Subject: Re: [PATCH v2 0/9] procfs: protect /proc/<pid>/* files with file->f_cred On Wed, Oct 2, 2013 at 3:37 PM, Djalal Harouni <tixxdz@...ndz.org> wrote: > 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() So we're talking about two kinds of attacks, right? Type 1: Unprivileged process does something like open("/proc/1/maps", O_RDONLY) and then passes the resulting fd to something privileged. Type 2: Unprivileged process does something like open("/proc/self/maps", O_RDONLY) and then forks. The parent calls execve on something privileged. Can we really not get away with fixing type 1 by preventing these files from being opened in the first place and type 2 by revoking all of these fds when a privilege-changing exec happens? I'm not objecting to your patches so much as thinking that read(2) has no business looking at current->cred *at all*. But maybe that ship has already sailed. --Andy > > >> --Andy >> > > -- > Djalal Harouni > http://opendz.org -- Andy Lutomirski AMA Capital Management, LLC
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