fix smb3-encryption breakage when CONFIG_DEBUG_SG=y

We can not use the standard sg_set_buf() fucntion since when
CONFIG_DEBUG_SG=y this adds a check that will BUG_ON for cifs.ko
when we pass it an object from the stack.

Create a new wrapper smb2_sg_set_buf() which avoids doing that particular check
and use it for smb3 encryption instead.

Signed-off-by: Ronnie Sahlberg <lsahlber@redhat.com>
Signed-off-by: Steve French <smfrench@gmail.com>
CC: Stable <stable@vger.kernel.org>

fs/cifs/smb2ops.c

@@ -2066,6 +2066,15 @@ fill_transform_hdr(struct smb2_transform_hdr *tr_hdr, struct smb_rqst *old_rq)
 	inc_rfc1001_len(tr_hdr, orig_len);
 }
 
+/* We can not use the normal sg_set_buf() as we will sometimes pass a
+ * stack object as buf.
+ */
+static inline void smb2_sg_set_buf(struct scatterlist *sg, const void *buf,
+				   unsigned int buflen)
+{
+	sg_set_page(sg, virt_to_page(buf), buflen, offset_in_page(buf));
+}
+
 static struct scatterlist *
 init_sg(struct smb_rqst *rqst, u8 *sign)
 {
@@ -2080,16 +2089,16 @@ init_sg(struct smb_rqst *rqst, u8 *sign)
 		return NULL;
 
 	sg_init_table(sg, sg_len);
-	sg_set_buf(&sg[0], rqst->rq_iov[0].iov_base + 24, assoc_data_len);
+	smb2_sg_set_buf(&sg[0], rqst->rq_iov[0].iov_base + 24, assoc_data_len);
 	for (i = 1; i < rqst->rq_nvec; i++)
-		sg_set_buf(&sg[i], rqst->rq_iov[i].iov_base,
+		smb2_sg_set_buf(&sg[i], rqst->rq_iov[i].iov_base,
 						rqst->rq_iov[i].iov_len);
 	for (j = 0; i < sg_len - 1; i++, j++) {
 		unsigned int len = (j < rqst->rq_npages - 1) ? rqst->rq_pagesz
 							: rqst->rq_tailsz;
 		sg_set_page(&sg[i], rqst->rq_pages[j], len, 0);
 	}
-	sg_set_buf(&sg[sg_len - 1], sign, SMB2_SIGNATURE_SIZE);
+	smb2_sg_set_buf(&sg[sg_len - 1], sign, SMB2_SIGNATURE_SIZE);
 	return sg;
 }