linux-kernel - [PATCH v2] apparmor: fix potential label refcnt leak in aa_change

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Message-Id: <1586063515-15682-1-git-send-email-xiyuyang19@fudan.edu.cn>
Date:   Sun,  5 Apr 2020 13:11:55 +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 v2] 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 aa_change_profile() return
and dropping unnecessary aa_get_current_label().

Signed-off-by: Xiyu Yang <xiyuyang19@...an.edu.cn>
Signed-off-by: Xin Tan <tanxin.ctf@...il.com>
---
Changes in v2:
- Remove unnecessary aa_get_current_label() because it gets called
  earlier in the fn
---
 security/apparmor/domain.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/security/apparmor/domain.c b/security/apparmor/domain.c
index 6ceb74e0f789..a84ef030fbd7 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;
 	}
@@ -1346,8 +1347,6 @@ int aa_change_profile(const char *fqname, int flags)
 			op = OP_CHANGE_PROFILE;
 	}
 
-	label = aa_get_current_label();
-
 	if (*fqname == '&') {
 		stack = true;
 		/* don't have label_parse() do stacking */
-- 
2.7.4