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From: Christian Brauner <brauner@kernel.org>
To: Michal Clapinski <mclapinski@google.com>
Cc: Jeff Layton <jlayton@kernel.org>,
	Chuck Lever <chuck.lever@oracle.com>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Shuah Khan <shuah@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jeff Xu <jeffxu@google.com>, Aleksa Sarai <cyphar@cyphar.com>,
	Daniel Verkamp <dverkamp@chromium.org>,
	Kees Cook <keescook@chromium.org>,
	Marc Dionne <marc.dionne@auristor.com>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-kselftest@vger.kernel.org
Subject: Re: [PATCH 1/2] fcntl: add fcntl(F_CHECK_ORIGINAL_MEMFD)
Date: Fri, 1 Sep 2023 14:56:14 +0200	[thread overview]
Message-ID: <20230901-lockt-erbfolge-e1f9a26f0d63@brauner> (raw)
In-Reply-To: <20230831203647.558079-2-mclapinski@google.com>

On Thu, Aug 31, 2023 at 10:36:46PM +0200, Michal Clapinski wrote:
> Add a way to check if an fd points to the memfd's original open fd
> (the one created by memfd_create).
> Useful because only the original open fd can be both writable and
> executable.
> 
> Signed-off-by: Michal Clapinski <mclapinski@google.com>
> ---
>  fs/fcntl.c                 | 3 +++
>  include/uapi/linux/fcntl.h | 9 +++++++++
>  2 files changed, 12 insertions(+)
> 
> diff --git a/fs/fcntl.c b/fs/fcntl.c
> index e871009f6c88..301527e07a4d 100644
> --- a/fs/fcntl.c
> +++ b/fs/fcntl.c
> @@ -419,6 +419,9 @@ static long do_fcntl(int fd, unsigned int cmd, unsigned long arg,
>  	case F_SET_RW_HINT:
>  		err = fcntl_rw_hint(filp, cmd, arg);
>  		break;
> +	case F_CHECK_ORIGINAL_MEMFD:
> +		err = !(filp->f_mode & FMODE_WRITER);
> +		break;

Honestly, make this an ioctl on memfds. This is so specific that it
really doesn't belong into fcntl().

  reply	other threads:[~2023-09-01 12:56 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-08-31 20:36 [PATCH 0/2] fcntl: add fcntl(F_CHECK_ORIGINAL_MEMFD) Michal Clapinski
2023-08-31 20:36 ` [PATCH 1/2] " Michal Clapinski
2023-09-01 12:56   ` Christian Brauner [this message]
2023-09-01 14:50     ` Michał Cłapiński
2023-09-01 18:34       ` Kees Cook
2023-09-04  7:29         ` Christian Brauner
2023-09-04 17:57           ` Michał Cłapiński
2023-09-05  8:37             ` Christian Brauner
2023-08-31 20:36 ` [PATCH 2/2] selftests: test fcntl(F_CHECK_ORIGINAL_MEMFD) Michal Clapinski

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