linux.git/kernel/fork.c, branch v4.4.177

fork: record start_time late

2019-01-13T09:05:32+00:00

commit 7b55851367136b1efd84d98fea81ba57a98304cf upstream.

This changes the fork(2) syscall to record the process start_time after
initializing the basic task structure but still before making the new
process visible to user-space.

Technically, we could record the start_time anytime during fork(2).  But
this might lead to scenarios where a start_time is recorded long before
a process becomes visible to user-space.  For instance, with
userfaultfd(2) and TLS, user-space can delay the execution of fork(2)
for an indefinite amount of time (and will, if this causes network
access, or similar).

By recording the start_time late, it much closer reflects the point in
time where the process becomes live and can be observed by other
processes.

Lastly, this makes it much harder for user-space to predict and control
the start_time they get assigned.  Previously, user-space could fork a
process and stall it in copy_thread_tls() before its pid is allocated,
but after its start_time is recorded.  This can be misused to later-on
cycle through PIDs and resume the stalled fork(2) yielding a process
that has the same pid and start_time as a process that existed before.
This can be used to circumvent security systems that identify processes
by their pid+start_time combination.

Even though user-space was always aware that start_time recording is
flaky (but several projects are known to still rely on start_time-based
identification), changing the start_time to be recorded late will help
mitigate existing attacks and make it much harder for user-space to
control the start_time a process gets assigned.

Reported-by: Jann Horn 
Signed-off-by: Tom Gundersen 
Signed-off-by: David Herrmann 
Signed-off-by: Linus Torvalds 
Signed-off-by: Greg Kroah-Hartman

kthread: Fix use-after-free if kthread fork fails

2018-09-19T20:48:55+00:00

commit 4d6501dce079c1eb6bf0b1d8f528a5e81770109e upstream.

If a kthread forks (e.g. usermodehelper since commit 1da5c46fa965) but
fails in copy_process() between calling dup_task_struct() and setting
p->set_child_tid, then the value of p->set_child_tid will be inherited
from the parent and get prematurely freed by free_kthread_struct().

    kthread()
     - worker_thread()
        - process_one_work()
        |  - call_usermodehelper_exec_work()
        |     - kernel_thread()
        |        - _do_fork()
        |           - copy_process()
        |              - dup_task_struct()
        |                 - arch_dup_task_struct()
        |                    - tsk->set_child_tid = current->set_child_tid // implied
        |              - ...
        |              - goto bad_fork_*
        |              - ...
        |              - free_task(tsk)
        |                 - free_kthread_struct(tsk)
        |                    - kfree(tsk->set_child_tid)
        - ...
        - schedule()
           - __schedule()
              - wq_worker_sleeping()
                 - kthread_data(task)->flags // UAF

The problem started showing up with commit 1da5c46fa965 since it reused
->set_child_tid for the kthread worker data.

A better long-term solution might be to get rid of the ->set_child_tid
abuse. The comment in set_kthread_struct() also looks slightly wrong.

Debugged-by: Jamie Iles 
Fixes: 1da5c46fa965 ("kthread: Make struct kthread kmalloc'ed")
Signed-off-by: Vegard Nossum 
Acked-by: Oleg Nesterov 
Cc: Peter Zijlstra 
Cc: Greg Kroah-Hartman 
Cc: Andy Lutomirski 
Cc: Frederic Weisbecker 
Cc: Jamie Iles 
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/20170509073959.17858-1-vegard.nossum@oracle.com
Signed-off-by: Thomas Gleixner 
Signed-off-by: Amit Pundir 
Signed-off-by: Greg Kroah-Hartman

fork: don't copy inconsistent signal handler state to child

2018-09-15T07:40:38+00:00

[ Upstream commit 06e62a46bbba20aa5286102016a04214bb446141 ]

Before this change, if a multithreaded process forks while one of its
threads is changing a signal handler using sigaction(), the memcpy() in
copy_sighand() can race with the struct assignment in do_sigaction().  It
isn't clear whether this can cause corruption of the userspace signal
handler pointer, but it definitely can cause inconsistency between
different fields of struct sigaction.

Take the appropriate spinlock to avoid this.

I have tested that this patch prevents inconsistency between sa_sigaction
and sa_flags, which is possible before this patch.

Link: http://lkml.kernel.org/r/20180702145108.73189-1-jannh@google.com
Signed-off-by: Jann Horn 
Acked-by: Michal Hocko 
Reviewed-by: Andrew Morton 
Cc: Rik van Riel 
Cc: "Peter Zijlstra (Intel)" 
Cc: Kees Cook 
Cc: Oleg Nesterov 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Signed-off-by: Sasha Levin 
Signed-off-by: Greg Kroah-Hartman

kaiser: stack map PAGE_SIZE at THREAD_SIZE-PAGE_SIZE

2018-01-05T14:44:23+00:00

Kaiser only needs to map one page of the stack; and
kernel/fork.c did not build on powerpc (no __PAGE_KERNEL).
It's all cleaner if linux/kaiser.h provides kaiser_map_thread_stack()
and kaiser_unmap_thread_stack() wrappers around asm/kaiser.h's
kaiser_add_mapping() and kaiser_remove_mapping().  And use
linux/kaiser.h in init/main.c to avoid the #ifdefs there.

Signed-off-by: Hugh Dickins 
Acked-by: Jiri Kosina 
Signed-off-by: Greg Kroah-Hartman

kaiser: merged update

2018-01-05T14:44:23+00:00

Merged fixes and cleanups, rebased to 4.4.89 tree (no 5-level paging).

Signed-off-by: Dave Hansen 
Signed-off-by: Hugh Dickins 
Acked-by: Jiri Kosina 
Signed-off-by: Greg Kroah-Hartman

KAISER: Kernel Address Isolation

2018-01-05T14:44:23+00:00

This patch introduces our implementation of KAISER (Kernel Address Isolation to
have Side-channels Efficiently Removed), a kernel isolation technique to close
hardware side channels on kernel address information.

More information about the patch can be found on:

        https://github.com/IAIK/KAISER

From: Richard Fellner 
From: Daniel Gruss 
X-Subject: [RFC, PATCH] x86_64: KAISER - do not map kernel in user mode
Date: Thu, 4 May 2017 14:26:50 +0200
Link: http://marc.info/?l=linux-kernel&m=149390087310405&w=2
Kaiser-4.10-SHA1: c4b1831d44c6144d3762ccc72f0c4e71a0c713e5

To: 
To: 
Cc: 
Cc: 
Cc: Michael Schwarz 
Cc: Richard Fellner 
Cc: Ingo Molnar 
Cc: 
Cc: 

After several recent works [1,2,3] KASLR on x86_64 was basically
considered dead by many researchers. We have been working on an
efficient but effective fix for this problem and found that not mapping
the kernel space when running in user mode is the solution to this
problem [4] (the corresponding paper [5] will be presented at ESSoS17).

With this RFC patch we allow anybody to configure their kernel with the
flag CONFIG_KAISER to add our defense mechanism.

If there are any questions we would love to answer them.
We also appreciate any comments!

Cheers,
Daniel (+ the KAISER team from Graz University of Technology)

[1] http://www.ieee-security.org/TC/SP2013/papers/4977a191.pdf
[2] https://www.blackhat.com/docs/us-16/materials/us-16-Fogh-Using-Undocumented-CPU-Behaviour-To-See-Into-Kernel-Mode-And-Break-KASLR-In-The-Process.pdf
[3] https://www.blackhat.com/docs/us-16/materials/us-16-Jang-Breaking-Kernel-Address-Space-Layout-Randomization-KASLR-With-Intel-TSX.pdf
[4] https://github.com/IAIK/KAISER
[5] https://gruss.cc/files/kaiser.pdf

[patch based also on
https://raw.githubusercontent.com/IAIK/KAISER/master/KAISER/0001-KAISER-Kernel-Address-Isolation.patch]

Signed-off-by: Richard Fellner 
Signed-off-by: Moritz Lipp 
Signed-off-by: Daniel Gruss 
Signed-off-by: Michael Schwarz 
Acked-by: Jiri Kosina 
Signed-off-by: Hugh Dickins 
Signed-off-by: Greg Kroah-Hartman

stackprotector: Increase the per-task stack canary's random range from 32 bits to 64 bits on 64-bit platforms

2017-06-14T11:16:23+00:00

commit 5ea30e4e58040cfd6434c2f33dc3ea76e2c15b05 upstream.

The stack canary is an 'unsigned long' and should be fully initialized to
random data rather than only 32 bits of random data.

Signed-off-by: Daniel Micay 
Acked-by: Arjan van de Ven 
Acked-by: Rik van Riel 
Acked-by: Kees Cook 
Cc: Arjan van Ven 
Cc: Linus Torvalds 
Cc: Peter Zijlstra 
Cc: Thomas Gleixner 
Cc: kernel-hardening@lists.openwall.com
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/20170504133209.3053-1-danielmicay@gmail.com
Signed-off-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

pid_ns: Fix race between setns'ed fork() and zap_pid_ns_processes()

2017-05-25T12:30:11+00:00

commit 3fd37226216620c1a468afa999739d5016fbc349 upstream.

Imagine we have a pid namespace and a task from its parent's pid_ns,
which made setns() to the pid namespace. The task is doing fork(),
while the pid namespace's child reaper is dying. We have the race
between them:

Task from parent pid_ns             Child reaper
copy_process()                      ..
  alloc_pid()                       ..
  ..                                zap_pid_ns_processes()
  ..                                  disable_pid_allocation()
  ..                                  read_lock(&tasklist_lock)
  ..                                  iterate over pids in pid_ns
  ..                                    kill tasks linked to pids
  ..                                  read_unlock(&tasklist_lock)
  write_lock_irq(&tasklist_lock);   ..
  attach_pid(p, PIDTYPE_PID);       ..
  ..                                ..

So, just created task p won't receive SIGKILL signal,
and the pid namespace will be in contradictory state.
Only manual kill will help there, but does the userspace
care about this? I suppose, the most users just inject
a task into a pid namespace and wait a SIGCHLD from it.

The patch fixes the problem. It simply checks for
(pid_ns->nr_hashed & PIDNS_HASH_ADDING) in copy_process().
We do it under the tasklist_lock, and can't skip
PIDNS_HASH_ADDING as noted by Oleg:

"zap_pid_ns_processes() does disable_pid_allocation()
and then takes tasklist_lock to kill the whole namespace.
Given that copy_process() checks PIDNS_HASH_ADDING
under write_lock(tasklist) they can't race;
if copy_process() takes this lock first, the new child will
be killed, otherwise copy_process() can't miss
the change in ->nr_hashed."

If allocation is disabled, we just return -ENOMEM
like it's made for such cases in alloc_pid().

v2: Do not move disable_pid_allocation(), do not
introduce a new variable in copy_process() and simplify
the patch as suggested by Oleg Nesterov.
Account the problem with double irq enabling
found by Eric W. Biederman.

Fixes: c876ad768215 ("pidns: Stop pid allocation when init dies")
Signed-off-by: Kirill Tkhai 
CC: Andrew Morton 
CC: Ingo Molnar 
CC: Peter Zijlstra 
CC: Oleg Nesterov 
CC: Mike Rapoport 
CC: Michal Hocko 
CC: Andy Lutomirski 
CC: "Eric W. Biederman" 
CC: Andrei Vagin 
CC: Cyrill Gorcunov 
CC: Serge Hallyn 
Acked-by: Oleg Nesterov 
Signed-off-by: Eric W. Biederman 
Signed-off-by: Greg Kroah-Hartman

kernek/fork.c: allocate idle task for a CPU always on its local node

2017-03-26T10:13:18+00:00

commit 725fc629ff2545b061407305ae51016c9f928fce upstream.

Linux preallocates the task structs of the idle tasks for all possible
CPUs.  This currently means they all end up on node 0.  This also
implies that the cache line of MWAIT, which is around the flags field in
the task struct, are all located in node 0.

We see a noticeable performance improvement on Knights Landing CPUs when
the cache lines used for MWAIT are located in the local nodes of the
CPUs using them.  I would expect this to give a (likely slight)
improvement on other systems too.

The patch implements placing the idle task in the node of its CPUs, by
passing the right target node to copy_process()

[akpm@linux-foundation.org: use NUMA_NO_NODE, not a bare -1]
Link: http://lkml.kernel.org/r/1463492694-15833-1-git-send-email-andi@firstfloor.org
Signed-off-by: Andi Kleen 
Cc: Thomas Gleixner 
Signed-off-by: Andrew Morton 
Signed-off-by: Linus Torvalds 
Cc: Sumit Semwal 
Signed-off-by: Greg Kroah-Hartman

mm: Add a user_ns owner to mm_struct and fix ptrace permission checks

2017-01-06T10:16:11+00:00

commit bfedb589252c01fa505ac9f6f2a3d5d68d707ef4 upstream.

During exec dumpable is cleared if the file that is being executed is
not readable by the user executing the file.  A bug in
ptrace_may_access allows reading the file if the executable happens to
enter into a subordinate user namespace (aka clone(CLONE_NEWUSER),
unshare(CLONE_NEWUSER), or setns(fd, CLONE_NEWUSER).

This problem is fixed with only necessary userspace breakage by adding
a user namespace owner to mm_struct, captured at the time of exec, so
it is clear in which user namespace CAP_SYS_PTRACE must be present in
to be able to safely give read permission to the executable.

The function ptrace_may_access is modified to verify that the ptracer
has CAP_SYS_ADMIN in task->mm->user_ns instead of task->cred->user_ns.
This ensures that if the task changes it's cred into a subordinate
user namespace it does not become ptraceable.

The function ptrace_attach is modified to only set PT_PTRACE_CAP when
CAP_SYS_PTRACE is held over task->mm->user_ns.  The intent of
PT_PTRACE_CAP is to be a flag to note that whatever permission changes
the task might go through the tracer has sufficient permissions for
it not to be an issue.  task->cred->user_ns is always the same
as or descendent of mm->user_ns.  Which guarantees that having
CAP_SYS_PTRACE over mm->user_ns is the worst case for the tasks
credentials.

To prevent regressions mm->dumpable and mm->user_ns are not considered
when a task has no mm.  As simply failing ptrace_may_attach causes
regressions in privileged applications attempting to read things
such as /proc//stat

Acked-by: Kees Cook 
Tested-by: Cyrill Gorcunov 
Fixes: 8409cca70561 ("userns: allow ptrace from non-init user namespaces")
Signed-off-by: "Eric W. Biederman" 
Signed-off-by: Greg Kroah-Hartman