netdev - Re: [PATCH 01/32] pidfs: validate extensible ioctls

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Message-ID: <2025-09-10-random-finer-pause-treasury-MBAX3P@cyphar.com>
Date: Thu, 11 Sep 2025 02:33:18 +1000
From: Aleksa Sarai <cyphar@...har.com>
To: Christian Brauner <brauner@...nel.org>
Cc: Jan Kara <jack@...e.cz>, Amir Goldstein <amir73il@...il.com>, 
	linux-fsdevel@...r.kernel.org, Josef Bacik <josef@...icpanda.com>, 
	Jeff Layton <jlayton@...nel.org>, Mike Yuan <me@...dnzj.com>, 
	Zbigniew Jędrzejewski-Szmek <zbyszek@...waw.pl>, Lennart Poettering <mzxreary@...inter.de>, 
	Daan De Meyer <daan.j.demeyer@...il.com>, Alexander Viro <viro@...iv.linux.org.uk>, 
	Jens Axboe <axboe@...nel.dk>, Tejun Heo <tj@...nel.org>, Johannes Weiner <hannes@...xchg.org>, 
	Michal Koutný <mkoutny@...e.com>, Eric Dumazet <edumazet@...gle.com>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, Simon Horman <horms@...nel.org>, 
	Chuck Lever <chuck.lever@...cle.com>, linux-nfs@...r.kernel.org, linux-kselftest@...r.kernel.org, 
	linux-block@...r.kernel.org, linux-kernel@...r.kernel.org, cgroups@...r.kernel.org, 
	netdev@...r.kernel.org
Subject: Re: [PATCH 01/32] pidfs: validate extensible ioctls

On 2025-09-10, Christian Brauner <brauner@...nel.org> wrote:
> Validate extensible ioctls stricter than we do now.
> 
> Signed-off-by: Christian Brauner <brauner@...nel.org>
> ---
>  fs/pidfs.c         |  2 +-
>  include/linux/fs.h | 14 ++++++++++++++
>  2 files changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/fs/pidfs.c b/fs/pidfs.c
> index edc35522d75c..0a5083b9cce5 100644
> --- a/fs/pidfs.c
> +++ b/fs/pidfs.c
> @@ -440,7 +440,7 @@ static bool pidfs_ioctl_valid(unsigned int cmd)
>  		 * erronously mistook the file descriptor for a pidfd.
>  		 * This is not perfect but will catch most cases.
>  		 */
> -		return (_IOC_TYPE(cmd) == _IOC_TYPE(PIDFD_GET_INFO));
> +		return extensible_ioctl_valid(cmd, PIDFD_GET_INFO, PIDFD_INFO_SIZE_VER0);
>  	}
>  
>  	return false;
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index d7ab4f96d705..2f2edc53bf3c 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -4023,4 +4023,18 @@ static inline bool vfs_empty_path(int dfd, const char __user *path)
>  
>  int generic_atomic_write_valid(struct kiocb *iocb, struct iov_iter *iter);
>  
> +static inline bool extensible_ioctl_valid(unsigned int cmd_a,
> +					  unsigned int cmd_b, size_t min_size)
> +{
> +	if (_IOC_DIR(cmd_a) != _IOC_DIR(cmd_b))
> +		return false;
> +	if (_IOC_TYPE(cmd_a) != _IOC_TYPE(cmd_b))
> +		return false;
> +	if (_IOC_NR(cmd_a) != _IOC_NR(cmd_b))
> +		return false;
> +	if (_IOC_SIZE(cmd_a) < min_size)
> +		return false;
> +	return true;
> +}
> +

nit: I know only we use them for now, but does this maybe belong in
ioctl.h (or even uaccess.h with the other extensible struct stuff)?

Otherwise,

Reviewed-by: Aleksa Sarai <cyphar@...har.com>

>  #endif /* _LINUX_FS_H */
> 
> -- 
> 2.47.3
> 

-- 
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
https://www.cyphar.com/

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