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From: Aurelien Jarno <aurelien@aurel32.net>
To: Matt Turner <mattst88@gmail.com>
Cc: libc-alpha@sourceware.org
Subject: Re: [PATCH] alpha: correct handling of negative *rlimit() args besides -1
Date: Mon, 10 Oct 2022 20:44:14 +0200	[thread overview]
Message-ID: <Y0Rn/oNmZ7BTvf3M@aurel32.net> (raw)
In-Reply-To: <20221008024522.523048-1-mattst88@gmail.com>

Hi,

On 2022-10-07 22:45, Matt Turner via Libc-alpha wrote:
> The generic version of RLIM_INFINITY in Linux is equal to (rlim_t)-1,
> which is equal to ULLONG_MAX.  On alpha however it is instead defined as
> 0x7ffffffffffffffful.  This was special-cased in 0d0bc78 [BZ #22648] but
> it specifically used an equality check.

I am not sure this commit is giving the full picture, commits around
should also be checked to understand it.

> There is a cpython test case test_prlimit_refcount which calls
> setrlimit() with { -2, -2 } as arguments rather than the usual -1, it
> therefore fails the equality test and is treated as a large arbitrary
> positive value past the maximum of RLIM_INFINITY and fails with EPERM.
> This patch changes the behavior of the *rlimit() calls to treat all
> integers between 0x7ffffffffffffffful and (rlim_t)-1 as (rlim_t)-1,
> i.e., RLIM_INFINITY.
 
Basically on alpha, the glibc API is now identical to the prlimit64 API,
which means there is a dead zone with invalid values from
0x8000000000000000ul to 0xfffffffffffffffeul. The kernel returns EPERM
for values in this range.

You suggestion is to consider values is this zone as infinity. I have
mixed feeling about that. From the setrlimit() side it looks like the
correct thing to do. But this breaks the assumption that calling
getrlimit() after a successful setrlimit() call will return the same
value.

> diff --git a/sysdeps/unix/sysv/linux/alpha/getrlimit64.c b/sysdeps/unix/sysv/linux/alpha/getrlimit64.c
> index c195f5b55c..40f3e6bdff 100644
> --- a/sysdeps/unix/sysv/linux/alpha/getrlimit64.c
> +++ b/sysdeps/unix/sysv/linux/alpha/getrlimit64.c
> @@ -38,11 +38,11 @@ __old_getrlimit64 (enum __rlimit_resource resource,
>    if (__getrlimit64 (resource, &krlimits) < 0)
>      return -1;
>  
> -  if (krlimits.rlim_cur == RLIM64_INFINITY)
> +  if (krlimits.rlim_cur >= OLD_RLIM64_INFINITY)
>      rlimits->rlim_cur = OLD_RLIM64_INFINITY;
>    else
>      rlimits->rlim_cur = krlimits.rlim_cur;
> -  if (krlimits.rlim_max == RLIM64_INFINITY)
> +  if (krlimits.rlim_max >= OLD_RLIM64_INFINITY)
>      rlimits->rlim_max = OLD_RLIM64_INFINITY;
>    else
>      rlimits->rlim_max = krlimits.rlim_max;

That said, I do not understand the change there. It is done on the
*compat* symbol which still uses the old glibc API definition. There we
want to keep doing the exact reverse operations as in the
rlim_to_rlim64() kernel function.

> diff --git a/sysdeps/unix/sysv/linux/alpha/setrlimit64.c b/sysdeps/unix/sysv/linux/alpha/setrlimit64.c
> index 421616ed20..4e88540a48 100644
> --- a/sysdeps/unix/sysv/linux/alpha/setrlimit64.c
> +++ b/sysdeps/unix/sysv/linux/alpha/setrlimit64.c
> @@ -35,11 +35,11 @@ __old_setrlimit64 (enum __rlimit_resource resource,
>  {
>    struct rlimit64 krlimits;
>  
> -  if (rlimits->rlim_cur == OLD_RLIM64_INFINITY)
> +  if (rlimits->rlim_cur >= OLD_RLIM64_INFINITY)
>      krlimits.rlim_cur = RLIM64_INFINITY;
>    else
>      krlimits.rlim_cur = rlimits->rlim_cur;
> -  if (rlimits->rlim_max == OLD_RLIM64_INFINITY)
> +  if (rlimits->rlim_max >= OLD_RLIM64_INFINITY)
>      krlimits.rlim_max = RLIM64_INFINITY;
>    else
>      krlimits.rlim_max = rlimits->rlim_max;

Ditto here we want to do the reverse operations as the rlim64_to_rlim()
kernel function.

-- 
Aurelien Jarno                          GPG: 4096R/1DDD8C9B
aurelien@aurel32.net                 http://www.aurel32.net

  parent reply	other threads:[~2022-10-10 18:44 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-10-08  2:45 Matt Turner
2022-10-10  0:51 ` Carlos O'Donell
2022-10-10  2:18   ` Matt Turner
2022-10-10 18:44 ` Aurelien Jarno [this message]
2023-02-14 19:38   ` matoro
2023-10-09  2:01     ` matoro

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