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From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     linux-kernel@vger.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, Kir Kolyshkin <kir@sacred.ru>,
        Ondrej Mosnacek <omosnace@redhat.com>,
        Paul Moore <paul@paul-moore.com>,
        Sasha Levin <sashal@kernel.org>
Subject: [PATCH 4.19 066/271] selinux: fix empty write to keycreate file
Date:   Wed, 24 Jul 2019 21:18:55 +0200
Message-Id: <20190724191700.851717639@linuxfoundation.org>
In-Reply-To: <20190724191655.268628197@linuxfoundation.org>
References: <20190724191655.268628197@linuxfoundation.org>
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[ Upstream commit 464c258aa45b09f16aa0f05847ed8895873262d9 ]

When sid == 0 (we are resetting keycreate_sid to the default value), we
should skip the KEY__CREATE check.

Before this patch, doing a zero-sized write to /proc/self/keycreate
would check if the current task can create unlabeled keys (which would
usually fail with -EACCESS and generate an AVC). Now it skips the check
and correctly sets the task's keycreate_sid to 0.

Bug report: https://bugzilla.redhat.com/show_bug.cgi?id=1719067

Tested using the reproducer from the report above.

Fixes: 4eb582cf1fbd ("[PATCH] keys: add a way to store the appropriate context for newly-created keys")
Reported-by: Kir Kolyshkin <kir@sacred.ru>
Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 security/selinux/hooks.c | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
index 70bad15ed7a0..109ab510bdb1 100644
--- a/security/selinux/hooks.c
+++ b/security/selinux/hooks.c
@@ -6550,11 +6550,12 @@ static int selinux_setprocattr(const char *name, void *value, size_t size)
 	} else if (!strcmp(name, "fscreate")) {
 		tsec->create_sid = sid;
 	} else if (!strcmp(name, "keycreate")) {
-		error = avc_has_perm(&selinux_state,
-				     mysid, sid, SECCLASS_KEY, KEY__CREATE,
-				     NULL);
-		if (error)
-			goto abort_change;
+		if (sid) {
+			error = avc_has_perm(&selinux_state, mysid, sid,
+					     SECCLASS_KEY, KEY__CREATE, NULL);
+			if (error)
+				goto abort_change;
+		}
 		tsec->keycreate_sid = sid;
 	} else if (!strcmp(name, "sockcreate")) {
 		tsec->sockcreate_sid = sid;
-- 
2.20.1