linux-kernel - Re: [PATCH] fs: correctly check for errors from replace_fd() in receive_fd

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Message-ID: <fq2s55tc5hhvh4dfjdzek4neozffmn36rwdlsrsxxjqzts2f4c@j67nruhocdiz>
Date: Fri, 1 Aug 2025 12:48:09 +0200
From: Jan Kara <jack@...e.cz>
To: Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Cc: Alexander Viro <viro@...iv.linux.org.uk>, 
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>, Sargun Dhillon <sargun@...gun.me>, 
	Kees Cook <kees@...nel.org>, linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, 
	stable@...r.kernel.org
Subject: Re: [PATCH] fs: correctly check for errors from replace_fd() in
 receive_fd_replace()

On Fri 01-08-25 09:38:38, Thomas Weißschuh wrote:
> replace_fd() returns either a negative error number or the number of the
> new file descriptor. The current code misinterprets any positive file
> descriptor number as an error.
> 
> Only check for negative error numbers, so that __receive_sock() is called
> correctly for valid file descriptors.
> 
> Fixes: 173817151b15 ("fs: Expand __receive_fd() to accept existing fd")
> Fixes: 42eb0d54c08a ("fs: split receive_fd_replace from __receive_fd")
> Cc: stable@...r.kernel.org
> Signed-off-by: Thomas Weißschuh <thomas.weissschuh@...utronix.de>

Indeed. I'm wondering how come nobody noticed... Feel free to add:

Reviewed-by: Jan Kara <jack@...e.cz>

								Honza

> ---
> Untested, it stuck out while reading the code.
> ---
>  fs/file.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/file.c b/fs/file.c
> index 6d2275c3be9c6967d16c75d1b6521f9b58980926..56c3a045121d8f43a54cf05e6ce1962f896339ac 100644
> --- a/fs/file.c
> +++ b/fs/file.c
> @@ -1387,7 +1387,7 @@ int receive_fd_replace(int new_fd, struct file *file, unsigned int o_flags)
>  	if (error)
>  		return error;
>  	error = replace_fd(new_fd, file, o_flags);
> -	if (error)
> +	if (error < 0)
>  		return error;
>  	__receive_sock(file);
>  	return new_fd;
> 
> ---
> base-commit: 89748acdf226fd1a8775ff6fa2703f8412b286c8
> change-id: 20250801-fix-receive_fd_replace-7fdd5ce6532d
> 
> Best regards,
> -- 
> Thomas Weißschuh <thomas.weissschuh@...utronix.de>
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR