crypto: caam - fix gfp allocation flags (part I)

Changes in the SW cts (ciphertext stealing) code in
commit 0605c41 ("crypto: cts - Convert to skcipher")
revealed a problem in the CAAM driver:
when cts(cbc(aes)) is executed and cts runs in SW,
cbc(aes) is offloaded in CAAM; cts encrypts the last block
in atomic context and CAAM incorrectly decides to use GFP_KERNEL
for memory allocation.

Fix this by allowing GFP_KERNEL (sleeping) only when MAY_SLEEP flag is
set, i.e. remove MAY_BACKLOG flag.

We split the fix in two parts - first is sent to -stable, while the
second is not (since there is no known failure case).

Link: http://lkml.kernel.org/g/20170602122446.2427-1-david@sigma-star.at
Cc: <stable@vger.kernel.org> # 4.8+
Reported-by: David Gstir <david@sigma-star.at>
Signed-off-by: Horia Geantă <horia.geanta@nxp.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/crypto/caam/caamalg.c

@@ -1475,8 +1475,7 @@ static struct ablkcipher_edesc *ablkcipher_edesc_alloc(struct ablkcipher_request
 	struct crypto_ablkcipher *ablkcipher = crypto_ablkcipher_reqtfm(req);
 	struct caam_ctx *ctx = crypto_ablkcipher_ctx(ablkcipher);
 	struct device *jrdev = ctx->jrdev;
-	gfp_t flags = (req->base.flags & (CRYPTO_TFM_REQ_MAY_BACKLOG |
-					  CRYPTO_TFM_REQ_MAY_SLEEP)) ?
+	gfp_t flags = (req->base.flags & CRYPTO_TFM_REQ_MAY_SLEEP) ?
 		       GFP_KERNEL : GFP_ATOMIC;
 	int src_nents, mapped_src_nents, dst_nents = 0, mapped_dst_nents = 0;
 	struct ablkcipher_edesc *edesc;