linux-kernel - [PATCH] apparmor: fix reference count leak in aa

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Message-Id: <20220428033907.1658-1-xiongx18@fudan.edu.cn>
Date:   Thu, 28 Apr 2022 11:39:08 +0800
From:   Xin Xiong <xiongx18@...an.edu.cn>
To:     John Johansen <john.johansen@...onical.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Seth Arnold <seth.arnold@...onical.com>,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     yuanxzhang@...an.edu.cn, Xin Xiong <xiongx18@...an.edu.cn>,
        Xiyu Yang <xiyuyang19@...an.edu.cn>,
        Xin Tan <tanxin.ctf@...il.com>
Subject: [PATCH] apparmor: fix reference count leak in aa_pivotroot()

The aa_pivotroot() function has a reference counting bug in a specific
path. When aa_replace_current_label() returns on success, the function
forgets to decrement the reference count of “target”, which is
increased earlier by build_pivotroot(), causing a reference leak.

Fix it by decreasing the refcount of “target” in that path.

Fixes: 2ea3ffb7782a ("apparmor: add mount mediation")
Co-developed-by: Xiyu Yang <xiyuyang19@...an.edu.cn>
Signed-off-by: Xiyu Yang <xiyuyang19@...an.edu.cn>
Co-developed-by: Xin Tan <tanxin.ctf@...il.com>
Signed-off-by: Xin Tan <tanxin.ctf@...il.com>
Signed-off-by: Xin Xiong <xiongx18@...an.edu.cn>
---
 security/apparmor/mount.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/security/apparmor/mount.c b/security/apparmor/mount.c
index aa6fcfde3051..d0b19ab9137d 100644
--- a/security/apparmor/mount.c
+++ b/security/apparmor/mount.c
@@ -718,6 +718,7 @@ int aa_pivotroot(struct aa_label *label, const struct path *old_path,
 			aa_put_label(target);
 			goto out;
 		}
+		aa_put_label(target);
 	} else
 		/* already audited error */
 		error = PTR_ERR(target);
-- 
2.25.1