From: "André Almeida" <andrealmeid@igalia.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org, mingo@redhat.com,
dvhart@infradead.org, dave@stgolabs.net, tglx@linutronix.de,
axboe@kernel.dk, Andrew Morton <akpm@linux-foundation.org>,
urezki@gmail.com, hch@infradead.org, lstoakes@gmail.com,
Arnd Bergmann <arnd@arndb.de>,
linux-api@vger.kernel.org, linux-mm@kvack.org,
linux-arch@vger.kernel.org, malteskarupke@web.de,
Geert Uytterhoeven <geert@linux-m68k.org>
Subject: Re: [PATCH v2 05/14] futex: Add sys_futex_wake()
Date: Thu, 10 Aug 2023 14:01:20 -0300 [thread overview]
Message-ID: <3bcdb026-8558-43ca-80c1-776216dcd86c@igalia.com> (raw)
In-Reply-To: <20230810121341.GX212435@hirez.programming.kicks-ass.net>
Em 10/08/2023 09:13, Peter Zijlstra escreveu:
> On Wed, Aug 09, 2023 at 07:25:19PM -0300, André Almeida wrote:
>> Hi Peter,
>>
>> Em 07/08/2023 09:18, Peter Zijlstra escreveu:
>>> To complement sys_futex_waitv() add sys_futex_wake(). This syscall
>>> implements what was previously known as FUTEX_WAKE_BITSET except it
>>> uses 'unsigned long' for the bitmask and takes FUTEX2 flags.
>>>
>>> The 'unsigned long' allows FUTEX2_SIZE_U64 on 64bit platforms.
>>>
>>> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
>>> Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
>>> ---
>>
>> [...]
>>
>>> +/*
>>> + * sys_futex_wake - Wake a number of futexes
>>> + * @uaddr: Address of the futex(es) to wake
>>> + * @mask: bitmask
>>> + * @nr: Number of the futexes to wake
>>> + * @flags: FUTEX2 flags
>>> + *
>>> + * Identical to the traditional FUTEX_WAKE_BITSET op, except it is part of the
>>> + * futex2 family of calls.
>>> + */
>>> +
>>> +SYSCALL_DEFINE4(futex_wake,
>>> + void __user *, uaddr,
>>> + unsigned long, mask,
>>> + int, nr,
>>> + unsigned int, flags)
>>> +{
>>
>> Do you think we could have a
>>
>> if (!nr)
>> return 0;
>>
>> here? Otherwise, calling futex_wake(&f, 0, flags) will wake 1 futex (if
>> available), which is a strange undocumented behavior in my opinion.
>
> Oh 'cute' that.. yeah, but how about I put it ...
>
>>> + if (flags & ~FUTEX2_VALID_MASK)
>>> + return -EINVAL;
>>> +
>>> + flags = futex2_to_flags(flags);
>>> + if (!futex_flags_valid(flags))
>>> + return -EINVAL;
>>> +
>>> + if (!futex_validate_input(flags, mask))
>>> + return -EINVAL;
>
> here, because otherwise we get:
>
> sys_futex_wake(&f, 0xFFFF, 0, FUTEX2_SIZE_U8)
>
> to return 0, even though that is 'obviously' nonsensical and should
> return -EINVAL. Or even garbage flags would be 'accepted'.
>
> (because 0xFFFF is larger than U8 can accomodate)
>
That make sense to me, but we would also want to validate the value of
f, if it's NULL or something strange to return -EINVAL... but this
happens only inside get_futex_key()...
To make this right, I think we would need to move this verification to
the syscall validation part:
if (unlikely((address % sizeof(u32)) != 0))
return -EINVAL;
if (unlikely(!access_ok(uaddr, sizeof(u32))))
return -EFAULT;
And have u32 replaced with the proper size being used.
>>> +
>>> + return futex_wake(uaddr, flags, nr, mask);
>>> +}
next prev parent reply other threads:[~2023-08-10 17:01 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-07 12:18 [PATCH v2 00/14] futex: More futex2 bits Peter Zijlstra
2023-08-07 12:18 ` [PATCH v2 01/14] futex: Clarify FUTEX2 flags Peter Zijlstra
2023-08-07 23:51 ` André Almeida
2023-08-07 12:18 ` [PATCH v2 02/14] futex: Extend the " Peter Zijlstra
2023-08-07 18:56 ` Thomas Gleixner
2023-08-08 0:02 ` André Almeida
2023-08-07 12:18 ` [PATCH v2 03/14] futex: Flag conversion Peter Zijlstra
2023-08-07 18:58 ` Thomas Gleixner
2023-08-08 0:52 ` André Almeida
2023-08-07 12:18 ` [PATCH v2 04/14] futex: Validate futex value against futex size Peter Zijlstra
2023-08-07 12:18 ` [PATCH v2 05/14] futex: Add sys_futex_wake() Peter Zijlstra
2023-08-07 19:00 ` Thomas Gleixner
2023-08-09 22:25 ` André Almeida
2023-08-10 12:13 ` Peter Zijlstra
2023-08-10 17:01 ` André Almeida [this message]
2023-08-07 12:18 ` [PATCH v2 06/14] futex: Add sys_futex_wait() Peter Zijlstra
2023-08-07 12:18 ` [PATCH v2 07/14] futex: Propagate flags into get_futex_key() Peter Zijlstra
2023-08-07 12:18 ` [PATCH v2 08/14] futex: Add flags2 argument to futex_requeue() Peter Zijlstra
2023-08-07 19:01 ` Thomas Gleixner
2023-08-07 12:18 ` [PATCH v2 09/14] futex: Add sys_futex_requeue() Peter Zijlstra
2023-08-07 19:05 ` Thomas Gleixner
2023-08-07 12:18 ` [PATCH v2 10/14] mm: Add vmalloc_huge_node() Peter Zijlstra
2023-08-07 12:18 ` [PATCH v2 11/14] futex: Implement FUTEX2_NUMA Peter Zijlstra
2023-08-07 21:11 ` Thomas Gleixner
2023-08-08 8:54 ` Peter Zijlstra
2023-08-08 9:12 ` Thomas Gleixner
2023-08-07 12:18 ` [PATCH v2 12/14] futex: Propagate flags into futex_get_value_locked() Peter Zijlstra
2023-08-07 21:12 ` Thomas Gleixner
2023-08-07 12:18 ` [PATCH v2 13/14] futex: Enable FUTEX2_{8,16} Peter Zijlstra
2023-08-07 21:15 ` Thomas Gleixner
2023-08-07 12:18 ` [PATCH v2 14/14] futex,selftests: Extend the futex selftests Peter Zijlstra
2023-08-08 20:32 ` [PATCH v2 00/14] futex: More futex2 bits Jens Axboe
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