From 514c9da48b860153079748b0d588cd42191f0b6a Mon Sep 17 00:00:00 2001
From: Guido Vranken <guidovranken@gmail.com>
Date: Mon, 22 Apr 2019 14:11:12 +0200
Subject: [PATCH] Enforce a strict output length check in CRYPTO_ccm128_tag

Return error if the output tag buffer size doesn't match
the tag size exactly. This prevents the caller from
using that portion of the tag buffer that remains
uninitialized after an otherwise succesfull call to
CRYPTO_ccm128_tag.

Bug found by OSS-Fuzz.

Fix suggested by Kurt Roeckx.

Signed-off-by: Guido Vranken <guidovranken@gmail.com>

Reviewed-by: Matthias St. Pierre <Matthias.St.Pierre@ncp-e.com>
Reviewed-by: Paul Dale <paul.dale@oracle.com>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/8810)
---
 crypto/modes/ccm128.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/crypto/modes/ccm128.c b/crypto/modes/ccm128.c
index 9edf0270e2c15..bfa2d4604caf4 100644
--- a/crypto/modes/ccm128.c
+++ b/crypto/modes/ccm128.c
@@ -425,7 +425,7 @@ size_t CRYPTO_ccm128_tag(CCM128_CONTEXT *ctx, unsigned char *tag, size_t len)
 
     M *= 2;
     M += 2;
-    if (len < M)
+    if (len != M)
         return 0;
     memcpy(tag, ctx->cmac.c, M);
     return M;