linux-kernel - Re: [PATCH] ovl: filter of trusted xattr results in audit

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Message-ID: <75330715-b83c-fa26-5dbd-745f71e9d592@android.com>
Date:   Mon, 7 Oct 2019 09:43:03 -0700
From:   Mark Salyzyn <salyzyn@...roid.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, kernel-team@...roid.com,
        linux-security-module@...r.kernel.org, stable@...r.kernel.org,
        Miklos Szeredi <miklos@...redi.hu>,
        linux-unionfs@...r.kernel.org
Subject: Re: [PATCH] ovl: filter of trusted xattr results in audit

On 10/7/19 9:40 AM, Greg Kroah-Hartman wrote:
> On Mon, Oct 07, 2019 at 06:17:25PM +0200, Greg Kroah-Hartman wrote:
>> On Mon, Oct 07, 2019 at 06:16:16PM +0200, Greg Kroah-Hartman wrote:
>>> On Mon, Oct 07, 2019 at 09:09:16AM -0700, Mark Salyzyn wrote:
>>>> When filtering xattr list for reading, presence of trusted xattr
>>>> results in a security audit log.  However, if there is other content
>>>> no errno will be set, and if there isn't, the errno will be -ENODATA
>>>> and not -EPERM as is usually associated with a lack of capability.
>>>> The check does not block the request to list the xattrs present.
>>>>
>>>> Switch to has_capability_noaudit to reflect a more appropriate check.
>>>>
>>>> Signed-off-by: Mark Salyzyn <salyzyn@...roid.com>
>>>> Cc: linux-security-module@...r.kernel.org
>>>> Cc: kernel-team@...roid.com
>>>> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
>>>> Cc: stable@...r.kernel.org # v3.18
>>>> Fixes: upstream a082c6f680da ("ovl: filter trusted xattr for non-admin")
>>>> Fixes: 3.18 4bcc9b4b3a0a ("ovl: filter trusted xattr for non-admin")
>>>> ---
>>>> Replaced ns_capable_noaudit with 3.18.y tree specific
>>>> has_capability_noaudit present in original submission to kernel.org
>>>> commit 5c2e9f346b815841f9bed6029ebcb06415caf640
>>>> ("ovl: filter of trusted xattr results in audit")
>>>>
>>>>   fs/overlayfs/inode.c | 3 ++-
>>>>   1 file changed, 2 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/fs/overlayfs/inode.c b/fs/overlayfs/inode.c
>>>> index a01ec1836a72..1175efa5e956 100644
>>>> --- a/fs/overlayfs/inode.c
>>>> +++ b/fs/overlayfs/inode.c
>>>> @@ -265,7 +265,8 @@ static bool ovl_can_list(const char *s)
>>>>   		return true;
>>>>   
>>>>   	/* Never list trusted.overlay, list other trusted for superuser only */
>>>> -	return !ovl_is_private_xattr(s) && capable(CAP_SYS_ADMIN);
>>>> +	return !ovl_is_private_xattr(s) &&
>>>> +	       has_capability_noaudit(current, CAP_SYS_ADMIN);
>>>>   }
>>>>   
>>>>   ssize_t ovl_listxattr(struct dentry *dentry, char *list, size_t size)
>>>> -- 
>>>> 2.23.0.581.g78d2f28ef7-goog
>>>>
>>> Thanks for the backport, this one worked!
>> I spoke too soon:
>>
>> ERROR: "has_capability_noaudit" [fs/overlayfs/overlay.ko] undefined!
>>
>> That function isn't exported for modules :(
> But, if this really is needed, and it fixes the issue, I'll go export
> that symbol with EXPORT_SYMBOL_GPL() to fix the problem.  Any
> objections?
>
> thanks,
>
> greg k-h

Ok, you just answered my question in cross-emails. Yes, 
EXPORT_SYMBOL_GPL() (my option 2).


Thanks


-- Mark Salyzyn