linux-kernel - Re: [PATCH] apparmor: fix potential label refcnt leak in aa_change

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Date:   Sat, 4 Apr 2020 16:35:16 -0700
From:   John Johansen <john.johansen@...onical.com>
To:     Xiyu Yang <xiyuyang19@...an.edu.cn>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     yuanxzhang@...an.edu.cn, kjlu@....edu,
        Xin Tan <tanxin.ctf@...il.com>
Subject: Re: [PATCH] apparmor: fix potential label refcnt leak in
 aa_change_profile

On 3/29/20 7:57 AM, Xiyu Yang wrote:
> aa_change_profile() invokes aa_get_current_label(), which returns
> a reference of the current task's label.
> 
> According to the comment of aa_get_current_label(), the returned
> reference must be put with aa_put_label().
> However, when the original object pointed by "label" becomes
> unreachable because aa_change_profile() returns or a new object
> is assigned to "label", reference count increased by
> aa_get_current_label() is not decreased, causing a refcnt leak.
> 
> Fix this by calling aa_put_label() before the original object pointed
> by "label" becomes unreachable.
> 
> Signed-off-by: Xiyu Yang <xiyuyang19@...an.edu.cn>
> Signed-off-by: Xin Tan <tanxin.ctf@...il.com>
> ---
>  security/apparmor/domain.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/security/apparmor/domain.c b/security/apparmor/domain.c
> index 6ceb74e0f789..b99145ae34c0 100644
> --- a/security/apparmor/domain.c
> +++ b/security/apparmor/domain.c
> @@ -1328,6 +1328,7 @@ int aa_change_profile(const char *fqname, int flags)
>  		ctx->nnp = aa_get_label(label);
>  
>  	if (!fqname || !*fqname) {
> +		aa_put_label(label);
>  		AA_DEBUG("no profile name");
>  		return -EINVAL;
>  	}
> @@ -1346,6 +1347,7 @@ int aa_change_profile(const char *fqname, int flags)
>  			op = OP_CHANGE_PROFILE;
>  	}
>  
> +	aa_put_label(label);
>  	label = aa_get_current_label();

this isn't quite right. Instead of adding the put_label here,
the aa_get_current_label needs to be dropped, as it isn't needed because
it gets called earlier in the fn.

can you refresh with this change

>  
>  	if (*fqname == '&') {
>