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Peter Zijlstra e552a8389a perf/core: Fix use-after-free in perf_release()
Dmitry reported syzcaller tripped a use-after-free in perf_release().

After much puzzlement Oleg spotted the below scenario:

  Task1                           Task2

  fork()
    perf_event_init_task()
    /* ... */
    goto bad_fork_$foo;
    /* ... */
    perf_event_free_task()
      mutex_lock(ctx->lock)
      perf_free_event(B)

                                  perf_event_release_kernel(A)
                                    mutex_lock(A->child_mutex)
                                    list_for_each_entry(child, ...) {
                                      /* child == B */
                                      ctx = B->ctx;
                                      get_ctx(ctx);
                                      mutex_unlock(A->child_mutex);

        mutex_lock(A->child_mutex)
        list_del_init(B->child_list)
        mutex_unlock(A->child_mutex)

        /* ... */

      mutex_unlock(ctx->lock);
      put_ctx() /* >0 */
    free_task();
                                      mutex_lock(ctx->lock);
                                      mutex_lock(A->child_mutex);
                                      /* ... */
                                      mutex_unlock(A->child_mutex);
                                      mutex_unlock(ctx->lock)
                                      put_ctx() /* 0 */
                                        ctx->task && !TOMBSTONE
                                          put_task_struct() /* UAF */

This patch closes the hole by making perf_event_free_task() destroy the
task <-> ctx relation such that perf_event_release_kernel() will no longer
observe the now dead task.

Spotted-by: Oleg Nesterov <oleg@redhat.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: fweisbec@gmail.com
Cc: oleg@redhat.com
Cc: stable@vger.kernel.org
Fixes: c6e5b73242 ("perf: Synchronously clean up child events")
Link: http://lkml.kernel.org/r/20170314155949.GE32474@worktop
Link: http://lkml.kernel.org/r/20170316125823.140295131@infradead.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
2017-03-16 14:16:52 +01:00
arch Merge branch 'linus' into perf/urgent, to resolve conflict 2017-03-02 08:05:45 +01:00
block lib/vsprintf.c: remove %Z support 2017-02-27 18:43:47 -08:00
certs certs: Add a secondary system keyring that can be added to dynamically 2016-04-11 22:48:09 +01:00
crypto crypto: change LZ4 modules to work with new LZ4 module version 2017-02-24 17:46:57 -08:00
Documentation Merge branch 'linus' into perf/urgent, to resolve conflict 2017-03-02 08:05:45 +01:00
drivers powerpc updates for 4.11 part 2 2017-03-01 10:10:16 -08:00
firmware WHENCE: use https://linuxtv.org for LinuxTV URLs 2015-12-04 10:35:11 -02:00
fs NFS client updates for Linux 4.11 2017-03-01 16:10:30 -08:00
include Merge branch 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-03-01 17:04:50 -08:00
init Merge branch 'idr-4.11' of git://git.infradead.org/users/willy/linux-dax 2017-02-28 20:29:41 -08:00
ipc ipc/shm: Fix shmat mmap nil-page protection 2017-02-27 18:43:46 -08:00
kernel perf/core: Fix use-after-free in perf_release() 2017-03-16 14:16:52 +01:00
lib Merge branch 'idr-4.11' of git://git.infradead.org/users/willy/linux-dax 2017-02-28 20:29:41 -08:00
mm Merge branch 'idr-4.11' of git://git.infradead.org/users/willy/linux-dax 2017-02-28 20:29:41 -08:00
net NFS client updates for Linux 4.11 2017-03-01 16:10:30 -08:00
samples Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-next 2017-02-22 10:15:09 -08:00
scripts objtool, modules: Discard objtool annotation sections for modules 2017-03-01 20:32:25 +01:00
security lib/vsprintf.c: remove %Z support 2017-02-27 18:43:47 -08:00
sound sound fixes for 4.11-rc1 2017-03-01 09:59:21 -08:00
tools objtool, modules: Discard objtool annotation sections for modules 2017-03-01 20:32:25 +01:00
usr kbuild: initramfs cleanup, set target from Kconfig 2017-01-05 09:40:16 -08:00
virt mm: add new mmget() helper 2017-02-27 18:43:48 -08:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Add hch to .get_maintainer.ignore 2015-08-21 14:30:10 -07:00
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore Merge branch 'misc' of git://git.kernel.org/pub/scm/linux/kernel/git/mmarek/kbuild 2016-08-02 16:48:52 -04:00
.mailmap mailmap: add codeaurora.org names for nameless email commits 2017-01-10 18:31:55 -08:00
COPYING
CREDITS MAINTAINERS: Remove old e-mail address 2017-02-13 12:24:56 -05:00
Kbuild scripts/gdb: provide linux constants 2016-05-23 17:04:14 -07:00
Kconfig
MAINTAINERS powerpc updates for 4.11 part 2 2017-03-01 10:10:16 -08:00
Makefile Merge branch 'core-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2017-02-28 10:15:59 -08:00
README README: add a new README file, pointing to the Documentation/ 2016-10-24 08:12:35 -02:00

Linux kernel
============

This file was moved to Documentation/admin-guide/README.rst

Please notice that there are several guides for kernel developers and users.
These guides can be rendered in a number of formats, like HTML and PDF.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.