linux-kernel - Re: [PATCH] tmpfs: clear S_ISGID when setting posix ACLs

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Date:   Fri, 6 Jan 2017 11:10:25 +0100
From:   Jan Kara <jack@...e.cz>
To:     Gu Zheng <guzheng1@...wei.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        viro@...iv.linux.org.uk, jack@...e.cz
Subject: Re: [PATCH] tmpfs: clear S_ISGID when setting posix ACLs

On Fri 06-01-17 16:12:55, Gu Zheng wrote:
> This change was missed the tmpfs modification in In CVE-2016-7097
> commit 073931017b49d9458aa351605b43a7e34598caef
> posix_acl: Clear SGID bit when setting file permissions.
> It can test by xfstest generic/375, which failed to clear
> setgid bit in the following test case on tmpfs:
> 
>   touch $testfile
>   chown 100:100 $testfile
>   chmod 2755 $testfile
>   _runas -u 100 -g 101 -- setfacl -m u::rwx,g::rwx,o::rwx $testfile
> 
> Signed-off-by: Gu Zheng <guzheng1@...wei.com>

Ah, good catch. One comment below:

> diff --git a/fs/posix_acl.c b/fs/posix_acl.c
> index 5955220..d014dff 100644
> --- a/fs/posix_acl.c
> +++ b/fs/posix_acl.c
> @@ -922,11 +922,10 @@ int simple_set_acl(struct inode *inode, struct posix_acl *acl, int type)
>  	int error;
>  
>  	if (type == ACL_TYPE_ACCESS) {
> -		error = posix_acl_equiv_mode(acl, &inode->i_mode);
> -		if (error < 0)
> -			return 0;
> -		if (error == 0)
> -			acl = NULL;
> +		error = posix_acl_update_mode(inode,
> +				&inode->i_mode, &acl);
> +		if (error > 0)
> +			return error;

Uh, why this error > 0 check? AFAIU it should be:

	if (error < 0)
		return 0;

As it used to be before...

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR