linux-kernel - Re: [PATCH] fanotify: Make sure to check event

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Message-ID: <20181205120921.GA30615@quack2.suse.cz>
Date:   Wed, 5 Dec 2018 13:09:21 +0100
From:   Jan Kara <jack@...e.cz>
To:     Kees Cook <keescook@...omium.org>
Cc:     Jan Kara <jack@...e.cz>, Heinrich Schuchardt <xypron.glpk@....de>,
        Amir Goldstein <amir73il@...il.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fanotify: Make sure to check event_len when copying

On Tue 04-12-18 15:44:46, Kees Cook wrote:
> As a precaution, make sure we check event_len when copying to userspace.
> Based on old feedback: https://lkml.kernel.org/r/542D9FE5.3010009@gmx.de
> 
> Signed-off-by: Kees Cook <keescook@...omium.org>

Thanks for the patch, I've added it to my tree.

								Honza

> ---
>  fs/notify/fanotify/fanotify_user.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
> index e03be5071362..d9484a0ac6b3 100644
> --- a/fs/notify/fanotify/fanotify_user.c
> +++ b/fs/notify/fanotify/fanotify_user.c
> @@ -206,7 +206,7 @@ static int process_access_response(struct fsnotify_group *group,
>  
>  static ssize_t copy_event_to_user(struct fsnotify_group *group,
>  				  struct fsnotify_event *event,
> -				  char __user *buf)
> +				  char __user *buf, size_t count)
>  {
>  	struct fanotify_event_metadata fanotify_event_metadata;
>  	struct file *f;
> @@ -220,6 +220,12 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group,
>  
>  	fd = fanotify_event_metadata.fd;
>  	ret = -EFAULT;
> +	/*
> +	 * Sanity check copy size in case get_one_event() and
> +	 * fill_event_metadata() event_len sizes ever get out of sync.
> +	 */
> +	if (WARN_ON_ONCE(fanotify_event_metadata.event_len > count))
> +		goto out_close_fd;
>  	if (copy_to_user(buf, &fanotify_event_metadata,
>  			 fanotify_event_metadata.event_len))
>  		goto out_close_fd;
> @@ -295,7 +301,7 @@ static ssize_t fanotify_read(struct file *file, char __user *buf,
>  			continue;
>  		}
>  
> -		ret = copy_event_to_user(group, kevent, buf);
> +		ret = copy_event_to_user(group, kevent, buf, count);
>  		if (unlikely(ret == -EOPENSTALE)) {
>  			/*
>  			 * We cannot report events with stale fd so drop it.
> -- 
> 2.17.1
> 
> 
> -- 
> Kees Cook
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR