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

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Date:   Sun, 29 Mar 2020 22:57:41 +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:     xiyuyang19@...an.edu.cn, yuanxzhang@...an.edu.cn, kjlu@....edu,
        Xin Tan <tanxin.ctf@...il.com>
Subject: [PATCH] apparmor: fix potential label refcnt leak in aa_change_profile

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();

 	if (*fqname == '&') {
-- 
2.7.4