linux-toradex.git/kernel/futex.c, branch v5.12-rc5

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

2021-03-16T21:13:10+00:00

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

Merge branch 'linus' into locking/core, to pick up upstream fixes

2021-02-12T11:54:58+00:00

Signed-off-by: Ingo Molnar

futex: Remove unneeded gotos

2021-01-28T12:20:18+00:00

Get rid of gotos that do not contain any cleanup. These were not removed in
commit 9180bd467f9a ("futex: Remove put_futex_key()").

Signed-off-by: Jangwoong Kim <6812skiii@gmail.com>
Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/r/20201230122953.10473-1-6812skiii@gmail.com

futex: Change utime parameter to be 'const ... *'

2021-01-28T12:20:18+00:00

futex(2) says that 'utime' is a pointer to 'const'.  The implementation
doesn't use 'const'; however, it _never_ modifies the contents of utime.

- futex() either uses 'utime' as a pointer to struct or as a 'u32'.

- In case it's used as a 'u32', it makes a copy of it, and of course it is
  not dereferenced.

- In case it's used as a 'struct __kernel_timespec __user *', the pointer
  is not dereferenced inside the futex() definition, and it is only passed
  to a function: get_timespec64(), which accepts a 'const struct
  __kernel_timespec __user *'.

[ tglx: Make the same change to the compat syscall and fixup the prototypes. ]

Signed-off-by: Alejandro Colomar 
Signed-off-by: Thomas Gleixner 
Link: https://lore.kernel.org/r/20201128123945.4592-1-alx.manpages@gmail.com

futex: Handle faults correctly for PI futexes

2021-01-26T14:11:00+00:00

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

futex: Simplify fixup_pi_state_owner()

2021-01-26T14:10:59+00:00

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

futex: Use pi_state_update_owner() in put_pi_state()

2021-01-26T14:10:59+00:00

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

rtmutex: Remove unused argument from rt_mutex_proxy_unlock()

2021-01-26T14:10:58+00:00

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

futex: Provide and use pi_state_update_owner()

2021-01-26T14:10:58+00:00

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

futex: Replace pointless printk in fixup_owner()

2021-01-26T14:10:58+00:00

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