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Date: Tue, 17 Aug 2021 13:01:12 +0200
From: Christian König <christian.koenig@....com>
To: David Hildenbrand <david@...hat.com>, linux-kernel@...r.kernel.org
Cc: Linus Torvalds <torvalds@...ux-foundation.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Thomas Gleixner <tglx@...utronix.de>,
Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
"H. Peter Anvin" <hpa@...or.com>,
Alexander Viro <viro@...iv.linux.org.uk>,
Alexey Dobriyan <adobriyan@...il.com>,
Steven Rostedt <rostedt@...dmis.org>,
Peter Zijlstra <peterz@...radead.org>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Mark Rutland <mark.rutland@....com>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Jiri Olsa <jolsa@...hat.com>,
Namhyung Kim <namhyung@...nel.org>,
Petr Mladek <pmladek@...e.com>,
Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
Rasmus Villemoes <linux@...musvillemoes.dk>,
Kees Cook <keescook@...omium.org>,
"Eric W. Biederman" <ebiederm@...ssion.com>,
Greg Ungerer <gerg@...ux-m68k.org>,
Geert Uytterhoeven <geert@...ux-m68k.org>,
Mike Rapoport <rppt@...nel.org>,
Vlastimil Babka <vbabka@...e.cz>,
Vincenzo Frascino <vincenzo.frascino@....com>,
Chinwen Chang <chinwen.chang@...iatek.com>,
Catalin Marinas <catalin.marinas@....com>,
"Matthew Wilcox (Oracle)" <willy@...radead.org>,
Huang Ying <ying.huang@...el.com>,
Jann Horn <jannh@...gle.com>, Feng Tang <feng.tang@...el.com>,
Kevin Brodsky <Kevin.Brodsky@....com>,
Michael Ellerman <mpe@...erman.id.au>,
Shawn Anastasio <shawn@...stas.io>,
Steven Price <steven.price@....com>,
Nicholas Piggin <npiggin@...il.com>,
Christian Brauner <christian.brauner@...ntu.com>,
Jens Axboe <axboe@...nel.dk>,
Gabriel Krisman Bertazi <krisman@...labora.com>,
Peter Xu <peterx@...hat.com>,
Suren Baghdasaryan <surenb@...gle.com>,
Shakeel Butt <shakeelb@...gle.com>,
Marco Elver <elver@...gle.com>,
Daniel Jordan <daniel.m.jordan@...cle.com>,
Nicolas Viennot <Nicolas.Viennot@...sigma.com>,
Thomas Cedeno <thomascedeno@...gle.com>,
Michal Hocko <mhocko@...e.com>,
Miklos Szeredi <miklos@...redi.hu>,
Chengguang Xu <cgxu519@...ernel.net>,
Florian Weimer <fweimer@...hat.com>,
David Laight <David.Laight@...LAB.COM>,
linux-unionfs@...r.kernel.org, linux-api@...r.kernel.org,
x86@...nel.org, linux-fsdevel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2 0/7] Remove in-tree usage of MAP_DENYWRITE
Am 16.08.21 um 21:48 schrieb David Hildenbrand:
> This series removes all in-tree usage of MAP_DENYWRITE from the kernel
> and removes VM_DENYWRITE. We stopped supporting MAP_DENYWRITE for
> user space applications a while ago because of the chance for DoS.
> The last renaming user is binfmt binary loading during exec and
> legacy library loading via uselib().
>
> With this change, MAP_DENYWRITE is effectively ignored throughout the
> kernel. Although the net change is small (well, we actually add code and
> comments), I think the cleanup in mmap() is quite nice.
>
> There are some (minor) user-visible changes with this series:
> 1. We no longer deny write access to shared libaries loaded via legacy
> uselib(); this behavior matches modern user space e.g., via dlopen().
> 2. We no longer deny write access to the elf interpreter after exec
> completed, treating it just like shared libraries (which it often is).
> 3. We always deny write access to the file linked via /proc/pid/exe:
> sys_prctl(PR_SET_MM_MAP/EXE_FILE) will fail if write access to the file
> cannot be denied, and write access to the file will remain denied
> until the link is effectivel gone (exec, termination,
> sys_prctl(PR_SET_MM_MAP/EXE_FILE)) -- just as if exec'ing the file.
>
> There is a related problem [2] with overlayfs, that should at least partly
> be tackled by this series. I don't quite understand the interaction of
> overlayfs and deny_write_access()/allow_write_access() at exec time:
>
> If we end up denying write access to the wrong file and not to the
> realfile, that would be fundamentally broken. We would have to reroute
> our deny_write_access()/ allow_write_access() calls for the exec file to
> the realfile -- but I leave figuring out the details to overlayfs guys, as
> that would be a related but different issue.
>
> There was a lengthy discussion in [3] whether to remove deny_write_access()
> completely; however, if we decide to go that way, it would ideally be done
> on top, because it could be that some applications even rely on the current
> behavior.
>
> v1 -> v2:
> - "kernel/fork: factor out replacing the current MM exe_file"
> -- Call the function "replace_mm_exe_file()" instead
> -- Add some doc, similar to set_mm_exe_file()
> -- Update patch subject/description
> - "kernel/fork: always deny write access to current MM exe_file"
> -- Introduce dup_mm_exe_file()
> -- Make set_mm_exe_file() return an error to make the code easier to
> grasp.
> -- Improve comments
> - Added ACKs
> - Mention "sys_prctl(PR_SET_MM_MAP/EXE_FILE)" everywhere instead of
> only "sys_prctl(PR_SET_MM_EXE_FILE)".
>
> RFC -> v1:
> - "binfmt: remove in-tree usage of MAP_DENYWRITE"
> -- Add a note that this should fix part of a problem with overlayfs
This is unfortunately way beyond my understanding of the fs layer to
actually review this.
But from the ten mile high view it looks like a really nice cleanup to
me and makes my live in the DRM subsystem much easier.
Feel free to add a Acked-by: Christian König <christian.koenig@....com>
to the series.
Thanks,
Christian.
>
> [1] https://lore.kernel.org/r/20210423131640.20080-1-david@redhat.com/
> [2] https://lore.kernel.org/r/YNHXzBgzRrZu1MrD@miu.piliscsaba.redhat.com/
> [3] https://lkml.kernel.org/r/20210812084348.6521-1-david@redhat.com
>
> Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Thomas Gleixner <tglx@...utronix.de>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> Cc: Alexander Viro <viro@...iv.linux.org.uk>
> Cc: Alexey Dobriyan <adobriyan@...il.com>
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Arnaldo Carvalho de Melo <acme@...nel.org>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
> Cc: Jiri Olsa <jolsa@...hat.com>
> Cc: Namhyung Kim <namhyung@...nel.org>
> Cc: Petr Mladek <pmladek@...e.com>
> Cc: Sergey Senozhatsky <sergey.senozhatsky@...il.com>
> Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> Cc: Rasmus Villemoes <linux@...musvillemoes.dk>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: "Eric W. Biederman" <ebiederm@...ssion.com>
> Cc: Greg Ungerer <gerg@...ux-m68k.org>
> Cc: Geert Uytterhoeven <geert@...ux-m68k.org>
> Cc: Mike Rapoport <rppt@...nel.org>
> Cc: Vlastimil Babka <vbabka@...e.cz>
> Cc: Vincenzo Frascino <vincenzo.frascino@....com>
> Cc: Chinwen Chang <chinwen.chang@...iatek.com>
> Cc: Catalin Marinas <catalin.marinas@....com>
> Cc: "Matthew Wilcox (Oracle)" <willy@...radead.org>
> Cc: Huang Ying <ying.huang@...el.com>
> Cc: Jann Horn <jannh@...gle.com>
> Cc: Feng Tang <feng.tang@...el.com>
> Cc: Kevin Brodsky <Kevin.Brodsky@....com>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: Shawn Anastasio <shawn@...stas.io>
> Cc: Steven Price <steven.price@....com>
> Cc: Nicholas Piggin <npiggin@...il.com>
> Cc: Christian Brauner <christian.brauner@...ntu.com>
> Cc: Jens Axboe <axboe@...nel.dk>
> Cc: Gabriel Krisman Bertazi <krisman@...labora.com>
> Cc: Peter Xu <peterx@...hat.com>
> Cc: Suren Baghdasaryan <surenb@...gle.com>
> Cc: Shakeel Butt <shakeelb@...gle.com>
> Cc: Marco Elver <elver@...gle.com>
> Cc: Daniel Jordan <daniel.m.jordan@...cle.com>
> Cc: Nicolas Viennot <Nicolas.Viennot@...sigma.com>
> Cc: Thomas Cedeno <thomascedeno@...gle.com>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Miklos Szeredi <miklos@...redi.hu>
> Cc: Chengguang Xu <cgxu519@...ernel.net>
> Cc: "Christian König" <ckoenig.leichtzumerken@...il.com>
> Cc: Florian Weimer <fweimer@...hat.com>
> Cc: Al Viro <viro@...iv.linux.org.uk>
> Cc: David Laight <David.Laight@...LAB.COM>
> Cc: linux-unionfs@...r.kernel.org
> Cc: linux-api@...r.kernel.org
> Cc: x86@...nel.org
> Cc: linux-fsdevel@...r.kernel.org
> Cc: linux-mm@...ck.org
>
> David Hildenbrand (7):
> binfmt: don't use MAP_DENYWRITE when loading shared libraries via
> uselib()
> kernel/fork: factor out replacing the current MM exe_file
> kernel/fork: always deny write access to current MM exe_file
> binfmt: remove in-tree usage of MAP_DENYWRITE
> mm: remove VM_DENYWRITE
> mm: ignore MAP_DENYWRITE in ksys_mmap_pgoff()
> fs: update documentation of get_write_access() and friends
>
> arch/x86/ia32/ia32_aout.c | 8 ++-
> fs/binfmt_aout.c | 7 ++-
> fs/binfmt_elf.c | 6 +--
> fs/binfmt_elf_fdpic.c | 2 +-
> fs/exec.c | 4 +-
> fs/proc/task_mmu.c | 1 -
> include/linux/fs.h | 19 ++++---
> include/linux/mm.h | 4 +-
> include/linux/mman.h | 4 +-
> include/trace/events/mmflags.h | 1 -
> kernel/events/core.c | 2 -
> kernel/fork.c | 95 ++++++++++++++++++++++++++++++----
> kernel/sys.c | 33 +-----------
> lib/test_printf.c | 5 +-
> mm/mmap.c | 29 ++---------
> mm/nommu.c | 2 -
> 16 files changed, 119 insertions(+), 103 deletions(-)
>
>
> base-commit: 7c60610d476766e128cc4284bb6349732cbd6606
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