target/iscsi: avoid NULL dereference in CHAP auth error path

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@users.sourceforge.net>
Signed-off-by: David Disseldorp <ddiss@suse.de>
Cc: stable@vger.kernel.org # 4.6+
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

diff --git a/drivers/target/iscsi/iscsi_target_auth.c b/drivers/target/iscsi/iscsi_target_auth.c
index f9bc8ec6fb6b5eb254b7d584c673a41c939a0ba5..9518ffd8b8bac81cc1b725046857d5f229e58b15 100644 (file)
--- a/drivers/target/iscsi/iscsi_target_auth.c
+++ b/drivers/target/iscsi/iscsi_target_auth.c
@@ -421,7 +421,8 @@ 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;