crypto: rsa-pkcs1pad - don't allocate buffer on stack

Avoid the s390 compile "warning: 'pkcs1pad_encrypt_sign_complete'
uses dynamic stack allocation" reported by kbuild test robot.  Don't
use a flat zero-filled buffer, instead zero the contents of the SGL.

Signed-off-by: Andrew Zaborowski <andrew.zaborowski@intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

1 files changed, 19 insertions, 8 deletions

diff --git a/crypto/rsa-pkcs1pad.c b/crypto/rsa-pkcs1pad.c
index accc67d16686..50f5c97e1087 100644
--- a/crypto/rsa-pkcs1pad.c
+++ b/crypto/rsa-pkcs1pad.c
@@ -110,21 +110,32 @@ static int pkcs1pad_encrypt_sign_complete(struct akcipher_request *req, int err)
         struct crypto_akcipher *tfm = crypto_akcipher_reqtfm(req);
         struct pkcs1pad_ctx *ctx = akcipher_tfm_ctx(tfm);
         struct pkcs1pad_request *req_ctx = akcipher_request_ctx(req);
-        uint8_t zeros[ctx->key_size - req_ctx->child_req.dst_len];
+        size_t pad_len = ctx->key_size - req_ctx->child_req.dst_len;
+        size_t chunk_len, pad_left;
+        struct sg_mapping_iter miter;
 
         if (!err) {
-                if (req_ctx->child_req.dst_len < ctx->key_size) {
-                        memset(zeros, 0, sizeof(zeros));
-                        sg_copy_from_buffer(req->dst,
-                                        sg_nents_for_len(req->dst,
-                                                sizeof(zeros)),
-                                        zeros, sizeof(zeros));
+                if (pad_len) {
+                        sg_miter_start(&miter, req->dst,
+                                        sg_nents_for_len(req->dst, pad_len),
+                                        SG_MITER_ATOMIC | SG_MITER_TO_SG);
+
+                        pad_left = pad_len;
+                        while (pad_left) {
+                                sg_miter_next(&miter);
+
+                                chunk_len = min(miter.length, pad_left);
+                                memset(miter.addr, 0, chunk_len);
+                                pad_left -= chunk_len;
+                        }
+
+                        sg_miter_stop(&miter);
                 }
 
                 sg_pcopy_from_buffer(req->dst,
                                 sg_nents_for_len(req->dst, ctx->key_size),
                                 req_ctx->out_buf, req_ctx->child_req.dst_len,
-                                sizeof(zeros));
+                                pad_len);
         }
         req->dst_len = ctx->key_size;