linux-kernel - [PATCH] apparmor: Fix aa_label refcnt leak in policy

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Date:   Mon, 20 Apr 2020 13:35:28 +0800
From:   Xiyu Yang <xiyuyang19@...an.edu.cn>
To:     John Johansen <john.johansen@...onical.com>,
        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,
        Xiyu Yang <xiyuyang19@...an.edu.cn>,
        Xin Tan <tanxin.ctf@...il.com>
Subject: [PATCH] apparmor: Fix aa_label refcnt leak in policy_update

policy_update() invokes begin_current_label_crit_section(), which
returns a reference of the updated aa_label object to "label" with
increased refcount.

When policy_update() returns, "label" becomes invalid, so the refcount
should be decreased to keep refcount balanced.

The reference counting issue happens in one exception handling path of
policy_update(). When aa_may_manage_policy() returns not NULL, the
refcnt increased by begin_current_label_crit_section() is not decreased,
causing a refcnt leak.

Fix this issue by jumping to "end_section" label when
aa_may_manage_policy() returns not NULL.

Signed-off-by: Xiyu Yang <xiyuyang19@...an.edu.cn>
Signed-off-by: Xin Tan <tanxin.ctf@...il.com>
---
 security/apparmor/apparmorfs.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/security/apparmor/apparmorfs.c b/security/apparmor/apparmorfs.c
index 280741fc0f5f..f6a3ecfadf80 100644
--- a/security/apparmor/apparmorfs.c
+++ b/security/apparmor/apparmorfs.c
@@ -454,7 +454,7 @@ static ssize_t policy_update(u32 mask, const char __user *buf, size_t size,
 	 */
 	error = aa_may_manage_policy(label, ns, mask);
 	if (error)
-		return error;
+		goto end_section;
 
 	data = aa_simple_write_to_buffer(buf, size, size, pos);
 	error = PTR_ERR(data);
@@ -462,6 +462,7 @@ static ssize_t policy_update(u32 mask, const char __user *buf, size_t size,
 		error = aa_replace_profiles(ns, label, mask, data);
 		aa_put_loaddata(data);
 	}
+end_section:
 	end_current_label_crit_section(label);
 
 	return error;
-- 
2.7.4