linux-stable.git/kernel/futex.c, branch v5.4.124

Revert 337f13046ff0 ("futex: Allow FUTEX_CLOCK_REALTIME with FUTEX_WAIT op")

2021-05-11T12:04:16+00:00

commit 4fbf5d6837bf81fd7a27d771358f4ee6c4f243f8 upstream.

The FUTEX_WAIT operand has historically a relative timeout which means that
the clock id is irrelevant as relative timeouts on CLOCK_REALTIME are not
subject to wall clock changes and therefore are mapped by the kernel to
CLOCK_MONOTONIC for simplicity.

If a caller would set FUTEX_CLOCK_REALTIME for FUTEX_WAIT the timeout is
still treated relative vs. CLOCK_MONOTONIC and then the wait arms that
timeout based on CLOCK_REALTIME which is broken and obviously has never
been used or even tested.

Reject any attempt to use FUTEX_CLOCK_REALTIME with FUTEX_WAIT again.

The desired functionality can be achieved with FUTEX_WAIT_BITSET and a
FUTEX_BITSET_MATCH_ANY argument.

Fixes: 337f13046ff0 ("futex: Allow FUTEX_CLOCK_REALTIME with FUTEX_WAIT op")
Signed-off-by: Thomas Gleixner 
Acked-by: Peter Zijlstra (Intel) 
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20210422194704.834797921@linutronix.de
Signed-off-by: Greg Kroah-Hartman

kernel, fs: Introduce and use set_restart_fn() and arch_set_restart_data()

2021-03-24T10:26:44+00:00

commit 5abbe51a526253b9f003e9a0a195638dc882d660 upstream.

Preparation for fixing get_nr_restart_syscall() on X86 for COMPAT.

Add a new helper which sets restart_block->fn and calls a dummy
arch_set_restart_data() helper.

Fixes: 609c19a385c8 ("x86/ptrace: Stop setting TS_COMPAT in ptrace code")
Signed-off-by: Oleg Nesterov 
Signed-off-by: Thomas Gleixner 
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20210201174641.GA17871@redhat.com
Signed-off-by: Greg Kroah-Hartman

futex: Handle faults correctly for PI futexes

2021-01-30T12:54:10+00:00

commit 34b1a1ce1458f50ef27c54e28eb9b1947012907a upstream

fixup_pi_state_owner() tries to ensure that the state of the rtmutex,
pi_state and the user space value related to the PI futex are consistent
before returning to user space. In case that the user space value update
faults and the fault cannot be resolved by faulting the page in via
fault_in_user_writeable() the function returns with -EFAULT and leaves
the rtmutex and pi_state owner state inconsistent.

A subsequent futex_unlock_pi() operates on the inconsistent pi_state and
releases the rtmutex despite not owning it which can corrupt the RB tree of
the rtmutex and cause a subsequent kernel stack use after free.

It was suggested to loop forever in fixup_pi_state_owner() if the fault
cannot be resolved, but that results in runaway tasks which is especially
undesired when the problem happens due to a programming error and not due
to malice.

As the user space value cannot be fixed up, the proper solution is to make
the rtmutex and the pi_state consistent so both have the same owner. This
leaves the user space value out of sync. Any subsequent operation on the
futex will fail because the 10th rule of PI futexes (pi_state owner and
user space value are consistent) has been violated.

As a consequence this removes the inept attempts of 'fixing' the situation
in case that the current task owns the rtmutex when returning with an
unresolvable fault by unlocking the rtmutex which left pi_state::owner and
rtmutex::owner out of sync in a different and only slightly less dangerous
way.

Fixes: 1b7558e457ed ("futexes: fix fault handling in futex_lock_pi")
Reported-by: gzobqq@gmail.com
Signed-off-by: Thomas Gleixner 
Acked-by: Peter Zijlstra (Intel) 
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman

futex: Simplify fixup_pi_state_owner()

2021-01-30T12:54:10+00:00

commit f2dac39d93987f7de1e20b3988c8685523247ae2 upstream

Too many gotos already and an upcoming fix would make it even more
unreadable.

Signed-off-by: Thomas Gleixner 
Acked-by: Peter Zijlstra (Intel) 
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman

futex: Use pi_state_update_owner() in put_pi_state()

2021-01-30T12:54:10+00:00

commit 6ccc84f917d33312eb2846bd7b567639f585ad6d upstream

No point in open coding it. This way it gains the extra sanity checks.

Signed-off-by: Thomas Gleixner 
Acked-by: Peter Zijlstra (Intel) 
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman

rtmutex: Remove unused argument from rt_mutex_proxy_unlock()

2021-01-30T12:54:09+00:00

commit 2156ac1934166d6deb6cd0f6ffc4c1076ec63697 upstream

Nothing uses the argument. Remove it as preparation to use
pi_state_update_owner().

Signed-off-by: Thomas Gleixner 
Acked-by: Peter Zijlstra (Intel) 
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman

futex: Provide and use pi_state_update_owner()

2021-01-30T12:54:09+00:00

commit c5cade200ab9a2a3be9e7f32a752c8d86b502ec7 upstream

Updating pi_state::owner is done at several places with the same
code. Provide a function for it and use that at the obvious places.

This is also a preparation for a bug fix to avoid yet another copy of the
same code or alternatively introducing a completely unpenetratable mess of
gotos.

Originally-by: Peter Zijlstra 
Signed-off-by: Thomas Gleixner 
Acked-by: Peter Zijlstra (Intel) 
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman

futex: Replace pointless printk in fixup_owner()

2021-01-30T12:54:09+00:00

commit 04b79c55201f02ffd675e1231d731365e335c307 upstream

If that unexpected case of inconsistent arguments ever happens then the
futex state is left completely inconsistent and the printk is not really
helpful. Replace it with a warning and make the state consistent.

Signed-off-by: Thomas Gleixner 
Acked-by: Peter Zijlstra (Intel) 
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman

futex: Ensure the correct return value from futex_lock_pi()

2021-01-30T12:54:09+00:00

commit 12bb3f7f1b03d5913b3f9d4236a488aa7774dfe9 upstream

In case that futex_lock_pi() was aborted by a signal or a timeout and the
task returned without acquiring the rtmutex, but is the designated owner of
the futex due to a concurrent futex_unlock_pi() fixup_owner() is invoked to
establish consistent state. In that case it invokes fixup_pi_state_owner()
which in turn tries to acquire the rtmutex again. If that succeeds then it
does not propagate this success to fixup_owner() and futex_lock_pi()
returns -EINTR or -ETIMEOUT despite having the futex locked.

Return success from fixup_pi_state_owner() in all cases where the current
task owns the rtmutex and therefore the futex and propagate it correctly
through fixup_owner(). Fixup the other callsite which does not expect a
positive return value.

Fixes: c1e2f0eaf015 ("futex: Avoid violating the 10th rule of futex")
Signed-off-by: Thomas Gleixner 
Acked-by: Peter Zijlstra (Intel) 
Cc: stable@vger.kernel.org
Signed-off-by: Greg Kroah-Hartman

futex: Don't enable IRQs unconditionally in put_pi_state()

2020-11-18T18:20:30+00:00

commit 1e106aa3509b86738769775969822ffc1ec21bf4 upstream.

The exit_pi_state_list() function calls put_pi_state() with IRQs disabled
and is not expecting that IRQs will be enabled inside the function.

Use the _irqsave() variant so that IRQs are restored to the original state
instead of being enabled unconditionally.

Fixes: 153fbd1226fb ("futex: Fix more put_pi_state() vs. exit_pi_state_list() races")
Signed-off-by: Dan Carpenter 
Signed-off-by: Thomas Gleixner 
Acked-by: Peter Zijlstra (Intel) 
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20201106085205.GA1159983@mwanda
Signed-off-by: Greg Kroah-Hartman