From 9c674e1e2f9e24fa4392167efe343749008338e0 Mon Sep 17 00:00:00 2001
From: Stephan Mueller <smueller@chronox.de>
Date: Thu, 18 Jan 2018 20:41:09 +0100
Subject: [PATCH] crypto: aesni - handle zero length dst buffer
Git-commit: 9c674e1e2f9e24fa4392167efe343749008338e0
Patch-mainline: v4.16-rc1
References: bsc#1051510

GCM can be invoked with a zero destination buffer. This is possible if
the AAD and the ciphertext have zero lengths and only the tag exists in
the source buffer (i.e. a source buffer cannot be zero). In this case,
the GCM cipher only performs the authentication and no decryption
operation.

When the destination buffer has zero length, it is possible that no page
is mapped to the SG pointing to the destination. In this case,
sg_page(req->dst) is an invalid access. Therefore, page accesses should
only be allowed if the req->dst->length is non-zero which is the
indicator that a page must exist.

This fixes a crash that can be triggered by user space via AF_ALG.

Cc: <stable@vger.kernel.org>
Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: Takashi Iwai <tiwai@suse.de>

---
 arch/x86/crypto/aesni-intel_glue.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/arch/x86/crypto/aesni-intel_glue.c
+++ b/arch/x86/crypto/aesni-intel_glue.c
@@ -827,7 +827,7 @@ static int helper_rfc4106_decrypt(struct
 	if (sg_is_last(req->src) &&
 	    (!PageHighMem(sg_page(req->src)) ||
 	    req->src->offset + req->src->length <= PAGE_SIZE) &&
-	    sg_is_last(req->dst) &&
+	    sg_is_last(req->dst) && req->dst->length &&
 	    (!PageHighMem(sg_page(req->dst)) ||
 	    req->dst->offset + req->dst->length <= PAGE_SIZE)) {
 		one_entry_in_sg = 1;