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Date:   Fri, 22 Mar 2019 12:14:46 +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, Dave Watson <davejwatson@...com>,
        Eric Biggers <ebiggers@...gle.com>,
        Herbert Xu <herbert@...dor.apana.org.au>
Subject: [PATCH 4.19 133/280] crypto: x86/aesni-gcm - fix crash on empty plaintext

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

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

From: Eric Biggers <ebiggers@...gle.com>

commit 3af349639597fea582a93604734d717e59a0e223 upstream.

gcmaes_crypt_by_sg() dereferences the NULL pointer returned by
scatterwalk_ffwd() when encrypting an empty plaintext and the source
scatterlist ends immediately after the associated data.

Fix it by only fast-forwarding to the src/dst data scatterlists if the
data length is nonzero.

This bug is reproduced by the "rfc4543(gcm(aes))" test vectors when run
with the new AEAD test manager.

Fixes: e845520707f8 ("crypto: aesni - Update aesni-intel_glue to use scatter/gather")
Cc: <stable@...r.kernel.org> # v4.17+
Cc: Dave Watson <davejwatson@...com>
Signed-off-by: Eric Biggers <ebiggers@...gle.com>
Signed-off-by: Herbert Xu <herbert@...dor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 arch/x86/crypto/aesni-intel_glue.c |   13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

--- a/arch/x86/crypto/aesni-intel_glue.c
+++ b/arch/x86/crypto/aesni-intel_glue.c
@@ -830,11 +830,14 @@ static int gcmaes_crypt_by_sg(bool enc,
 		scatterwalk_map_and_copy(assoc, req->src, 0, assoclen, 0);
 	}
 
-	src_sg = scatterwalk_ffwd(src_start, req->src, req->assoclen);
-	scatterwalk_start(&src_sg_walk, src_sg);
-	if (req->src != req->dst) {
-		dst_sg = scatterwalk_ffwd(dst_start, req->dst, req->assoclen);
-		scatterwalk_start(&dst_sg_walk, dst_sg);
+	if (left) {
+		src_sg = scatterwalk_ffwd(src_start, req->src, req->assoclen);
+		scatterwalk_start(&src_sg_walk, src_sg);
+		if (req->src != req->dst) {
+			dst_sg = scatterwalk_ffwd(dst_start, req->dst,
+						  req->assoclen);
+			scatterwalk_start(&dst_sg_walk, dst_sg);
+		}
 	}
 
 	kernel_fpu_begin();


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