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Date: Mon, 15 Jan 2018 16:19:16 +0100
From: Heiko Carstens <heiko.carstens@de.ibm.com>
To: Eugene Syromiatnikov <esyr@redhat.com>
Cc: linux-s390@vger.kernel.org,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Paul Gortmaker <paul.gortmaker@windriver.com>,
        Philippe Ombredanne <pombredanne@nexb.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Kate Stewart <kstewart@linuxfoundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] s390: fix setgid16/setuid16 handling of -1
References: <20180115115242.GA15131@asgard.redhat.com>
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On Mon, Jan 15, 2018 at 12:52:42PM +0100, Eugene Syromiatnikov wrote:
> For some reason, the implementation of these two 16-bit ID system calls
> used cast instead of low2highgid/low2highuid macros for converting [GU]IDs,
> which leads to incorrect handling of value of -1 (which ought to be
> considered invalid).
> 
> Discovered by strace test suite.
> 
> Signed-off-by: Eugene Syromiatnikov <esyr@redhat.com>
> ---
>  arch/s390/kernel/compat_linux.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/s390/kernel/compat_linux.c b/arch/s390/kernel/compat_linux.c
> index f04db37..e48a31a 100644
> --- a/arch/s390/kernel/compat_linux.c
> +++ b/arch/s390/kernel/compat_linux.c
> @@ -110,7 +110,7 @@ COMPAT_SYSCALL_DEFINE2(s390_setregid16, u16, rgid, u16, egid)
> 
>  COMPAT_SYSCALL_DEFINE1(s390_setgid16, u16, gid)
>  {
> -	return sys_setgid((gid_t)gid);
> +	return sys_setgid(low2highgid(gid));
>  }
> 
>  COMPAT_SYSCALL_DEFINE2(s390_setreuid16, u16, ruid, u16, euid)
> @@ -120,7 +120,7 @@ COMPAT_SYSCALL_DEFINE2(s390_setreuid16, u16, ruid, u16, euid)
> 
>  COMPAT_SYSCALL_DEFINE1(s390_setuid16, u16, uid)
>  {
> -	return sys_setuid((uid_t)uid);
> +	return sys_setuid(low2highuid(uid));

Thank you! Would you mind to fix this also for s390_setfsuid16 and
s390_setfsgid16 within the same file, and resend?