linux-kernel - [PATCH 5.4 067/111] apparmor: fix potential label refcnt leak in aa_change

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Message-Id: <20200526183939.201163831@linuxfoundation.org>
Date:   Tue, 26 May 2020 20:53:25 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Xiyu Yang <xiyuyang19@...an.edu.cn>,
        Xin Tan <tanxin.ctf@...il.com>,
        John Johansen <john.johansen@...onical.com>
Subject: [PATCH 5.4 067/111] apparmor: fix potential label refcnt leak in aa_change_profile

From: Xiyu Yang <xiyuyang19@...an.edu.cn>

commit a0b845ffa0d91855532b50fc040aeb2d8338dca4 upstream.

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 aa_change_profile() return
and dropping unnecessary aa_get_current_label().

Fixes: 9fcf78cca198 ("apparmor: update domain transitions that are subsets of confinement at nnp")
Signed-off-by: Xiyu Yang <xiyuyang19@...an.edu.cn>
Signed-off-by: Xin Tan <tanxin.ctf@...il.com>
Signed-off-by: John Johansen <john.johansen@...onical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 security/apparmor/domain.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/security/apparmor/domain.c
+++ b/security/apparmor/domain.c
@@ -1334,6 +1334,7 @@ int aa_change_profile(const char *fqname
 		ctx->nnp = aa_get_label(label);
 
 	if (!fqname || !*fqname) {
+		aa_put_label(label);
 		AA_DEBUG("no profile name");
 		return -EINVAL;
 	}
@@ -1352,8 +1353,6 @@ int aa_change_profile(const char *fqname
 			op = OP_CHANGE_PROFILE;
 	}
 
-	label = aa_get_current_label();
-
 	if (*fqname == '&') {
 		stack = true;
 		/* don't have label_parse() do stacking */