ACK: [CVE-2017-5551][PATCHv2 Yakkety] tmpfs: clear S_ISGID when setting posix ACLs

[Stefan Bader]

On 27.06.2017 08:52, Po-Hsu Lin wrote:
> From: Gu Zheng <guzheng1 at huawei.com>
> 
> CVE-2017-5551
> 
> This change was missed the tmpfs modification in In CVE-2016-7097
> commit 073931017b49 ("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 at huawei.com>
> Signed-off-by: Al Viro <viro at zeniv.linux.org.uk>
> (cherry picked from commit 497de07d89c1410d76a15bec2bb41f24a2a89f31)
> 
> Signed-off-by: Po-Hsu Lin <po-hsu.lin at canonical.com>
Acked-by: Stefan Bader <stefan.bader at canonical.com>

> ---
>  fs/posix_acl.c |    9 ++++-----
>  1 file changed, 4 insertions(+), 5 deletions(-)
> 
> diff --git a/fs/posix_acl.c b/fs/posix_acl.c
> index adf1e18..df15c56 100644
> --- a/fs/posix_acl.c
> +++ b/fs/posix_acl.c
> @@ -931,11 +931,10 @@ 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)
> +			return error;
>  	}
>  
>  	inode->i_ctime = CURRENT_TIME;
> 


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