linux-kernel - Re: [PATCH v2 1/2] fs/sysctl: fix potential page fault while unregistering sysctl table

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Date:   Wed, 28 Feb 2018 01:09:05 +0000
From:   "Luis R. Rodriguez" <mcgrof@...nel.org>
To:     Danilo Krummrich <danilokrummrich@...develop.de>
Cc:     mcgrof@...nel.org, keescook@...omium.org,
        linux-kernel@...r.kernel.org,
        Eric Biederman <ebiederm@...ssion.com>,
        linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] fs/sysctl: fix potential page fault while
 unregistering sysctl table

On Wed, Feb 28, 2018 at 12:31:55AM +0100, Danilo Krummrich wrote:
> proc_sys_link_fill_cache() does not take currently unregistering
> sysctl tables into account, which might result into a page fault in
> sysctl_follow_link() - add a check to fix it.
> 
> Signed-off-by: Danilo Krummrich <danilokrummrich@...develop.de>
> ---
> v2: removed empty line between between sysctl_head_grab and IS_ERR

Please add a respective tag:

Fixes: 0e47c99d7fe25 ("sysctl: Replace root_list with links between sysctl_table_sets")

And mention this has been present since v3.4. May be worth sending to
stable as well, so peg stable as well.

  Luis

> ---
>  fs/proc/proc_sysctl.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c
> index c5cbbdff3c3d..82ac5f682b73 100644
> --- a/fs/proc/proc_sysctl.c
> +++ b/fs/proc/proc_sysctl.c
> @@ -707,7 +707,10 @@ static bool proc_sys_link_fill_cache(struct file *file,
>  				    struct ctl_table *table)
>  {
>  	bool ret = true;
> +
>  	head = sysctl_head_grab(head);
> +	if (IS_ERR(head))
> +		return false;
>  
>  	if (S_ISLNK(table->mode)) {
>  		/* It is not an error if we can not follow the link ignore it */
> -- 
> 2.14.1
> 
> 

-- 
Luis Rodriguez, SUSE LINUX GmbH
Maxfeldstrasse 5; D-90409 Nuernberg