linux-kernel - Re: [PATCH v5 3/3] fs: pipe2: Support O_SPECIFIC

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Date:   Wed, 22 Apr 2020 17:44:38 +0200
From:   Florian Weimer <fw@...eb.enyo.de>
To:     Mark Wielaard <mark@...mp.org>
Cc:     Josh Triplett <josh@...htriplett.org>, io-uring@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        mtk.manpages@...il.com, Alexander Viro <viro@...iv.linux.org.uk>,
        Arnd Bergmann <arnd@...db.de>, Jens Axboe <axboe@...nel.dk>,
        Aleksa Sarai <cyphar@...har.com>, linux-man@...r.kernel.org
Subject: Re: [PATCH v5 3/3] fs: pipe2: Support O_SPECIFIC_FD

* Josh Triplett:

> This allows the caller of pipe2 to specify one or both file descriptors
> rather than having them automatically use the lowest available file
> descriptor. The caller can specify either file descriptor as -1 to
> allow that file descriptor to use the lowest available.
>
> Signed-off-by: Josh Triplett <josh@...htriplett.org>
> ---
>  fs/pipe.c | 16 ++++++++++++----
>  1 file changed, 12 insertions(+), 4 deletions(-)
>
> diff --git a/fs/pipe.c b/fs/pipe.c
> index 16fb72e9abf7..4681a0d1d587 100644
> --- a/fs/pipe.c
> +++ b/fs/pipe.c
> @@ -936,19 +936,19 @@ static int __do_pipe_flags(int *fd, struct file **files, int flags)
>  	int error;
>  	int fdw, fdr;
>  
> -	if (flags & ~(O_CLOEXEC | O_NONBLOCK | O_DIRECT))
> +	if (flags & ~(O_CLOEXEC | O_NONBLOCK | O_DIRECT | O_SPECIFIC_FD))
>  		return -EINVAL;
>  
>  	error = create_pipe_files(files, flags);
>  	if (error)
>  		return error;
>  
> -	error = get_unused_fd_flags(flags);
> +	error = get_specific_unused_fd_flags(fd[0], flags);
>  	if (error < 0)
>  		goto err_read_pipe;
>  	fdr = error;
>  
> -	error = get_unused_fd_flags(flags);
> +	error = get_specific_unused_fd_flags(fd[1], flags);
>  	if (error < 0)
>  		goto err_fdr;
>  	fdw = error;
> @@ -969,7 +969,11 @@ static int __do_pipe_flags(int *fd, struct file **files, int flags)
>  int do_pipe_flags(int *fd, int flags)
>  {
>  	struct file *files[2];
> -	int error = __do_pipe_flags(fd, files, flags);
> +	int error;
> +
> +	if (flags & O_SPECIFIC_FD)
> +		return -EINVAL;
> +	error = __do_pipe_flags(fd, files, flags);
>  	if (!error) {
>  		fd_install(fd[0], files[0]);
>  		fd_install(fd[1], files[1]);
> @@ -987,6 +991,10 @@ static int do_pipe2(int __user *fildes, int flags)
>  	int fd[2];
>  	int error;
>  
> +	if (flags & O_SPECIFIC_FD)
> +		if (copy_from_user(fd, fildes, sizeof(fd)))
> +			return -EFAULT;
> +
>  	error = __do_pipe_flags(fd, files, flags);
>  	if (!error) {
>  		if (unlikely(copy_to_user(fildes, fd, sizeof(fd)))) {

Mark, I think this will need (or at least benefit from) some valgrind
changes.