linux-kernel - [PATCH 4.9 17/77] target/iscsi: avoid NULL dereference in CHAP auth error path

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Date:   Wed, 21 Feb 2018 13:48:26 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org,
        Markus Elfring <elfring@...rs.sourceforge.net>,
        David Disseldorp <ddiss@...e.de>,
        Nicholas Bellinger <nab@...ux-iscsi.org>
Subject: [PATCH 4.9 17/77] target/iscsi: avoid NULL dereference in CHAP auth error path

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: David Disseldorp <ddiss@...e.de>

commit ce512d79d0466a604793addb6b769d12ee326822 upstream.

If chap_server_compute_md5() fails early, e.g. via CHAP_N mismatch, then
crypto_free_shash() is called with a NULL pointer which gets
dereferenced in crypto_shash_tfm().

Fixes: 69110e3cedbb ("iscsi-target: Use shash and ahash")
Suggested-by: Markus Elfring <elfring@...rs.sourceforge.net>
Signed-off-by: David Disseldorp <ddiss@...e.de>
Cc: stable@...r.kernel.org # 4.6+
Signed-off-by: Nicholas Bellinger <nab@...ux-iscsi.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/target/iscsi/iscsi_target_auth.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/target/iscsi/iscsi_target_auth.c
+++ b/drivers/target/iscsi/iscsi_target_auth.c
@@ -413,7 +413,8 @@ static int chap_server_compute_md5(
 	auth_ret = 0;
 out:
 	kzfree(desc);
-	crypto_free_shash(tfm);
+	if (tfm)
+		crypto_free_shash(tfm);
 	kfree(challenge);
 	kfree(challenge_binhex);
 	return auth_ret;