[SMB2] buffer handling

[tridge at samba.org]

Metze,

 > This allows us to distinguish between a NULL buffer and a zero length
 > buffer. And it also handle padding of the buffers.

Following up to our discussion on IRC, what do you think about this
approach?

Note in particulat the smb2_oob() change. We need that as we need to
allow offsets pointing outside the packet, as long as the length is
zero bytes.

Cheers, Tridge

diff --git a/source/libcli/smb2/request.c b/source/libcli/smb2/request.c
index 7a0311f..886ac5a 100644
--- a/source/libcli/smb2/request.c
+++ b/source/libcli/smb2/request.c
@@ -206,6 +206,10 @@ bool smb2_request_is_ok(struct smb2_request *req)
 */
 bool smb2_oob(struct smb2_request_buffer *buf, const uint8_t *ptr, size_t size)
 {
+	if (size == 0) {
+		/* zero bytes is never out of range */
+		return false;
+	}
 	/* be careful with wraparound! */
 	if (ptr < buf->body ||
 	    ptr >= buf->body + buf->body_size ||
@@ -270,7 +274,7 @@ NTSTATUS smb2_pull_o16s16_blob(struct smb2_request_buffer *buf, TALLOC_CTX *mem_
 	}
 	ofs  = SVAL(ptr, 0);
 	size = SVAL(ptr, 2);
-	if (ofs == 0 || size == 0) {
+	if (ofs == 0) {
 		*blob = data_blob(NULL, 0);
 		return NT_STATUS_OK;
 	}
@@ -310,7 +314,10 @@ NTSTATUS smb2_push_o16s16_blob(struct smb2_request_buffer *buf,
 		return NT_STATUS_BUFFER_TOO_SMALL;
 	}
 
-	if (blob.length == 0) {
+	if (blob.data == NULL) {
+		if (blob.length != 0) {
+			return NT_STATUS_INTERNAL_ERROR;
+		}
 		SSVAL(ptr, 0, 0);
 		SSVAL(ptr, 2, 0);
 		return NT_STATUS_OK;
@@ -363,7 +370,10 @@ NTSTATUS smb2_push_o16s32_blob(struct smb2_request_buffer *buf,
 		return NT_STATUS_BUFFER_TOO_SMALL;
 	}
 
-	if (blob.length == 0) {
+	if (blob.data == NULL) {
+		if (blob.length != 0) {
+			return NT_STATUS_INTERNAL_ERROR;
+		}
 		SSVAL(ptr, 0, 0);
 		SIVAL(ptr, 2, 0);
 		return NT_STATUS_OK;
@@ -416,7 +426,10 @@ NTSTATUS smb2_push_o32s32_blob(struct smb2_request_buffer *buf,
 		return NT_STATUS_BUFFER_TOO_SMALL;
 	}
 
-	if (blob.length == 0) {
+	if (blob.data == NULL) {
+		if (blob.length != 0) {
+			return NT_STATUS_INTERNAL_ERROR;
+		}
 		SIVAL(ptr, 0, 0);
 		SIVAL(ptr, 4, 0);
 		return NT_STATUS_OK;
@@ -469,7 +482,10 @@ NTSTATUS smb2_push_s32o32_blob(struct smb2_request_buffer *buf,
 		return NT_STATUS_BUFFER_TOO_SMALL;
 	}
 
-	if (blob.length == 0) {
+	if (blob.data == NULL) {
+		if (blob.length != 0) {
+			return NT_STATUS_INTERNAL_ERROR;
+		}
 		SIVAL(ptr, 0, 0);
 		SIVAL(ptr, 4, 0);
 		return NT_STATUS_OK;
@@ -512,7 +528,7 @@ NTSTATUS smb2_pull_o16s32_blob(struct smb2_request_buffer *buf, TALLOC_CTX *mem_
 	}
 	ofs  = SVAL(ptr, 0);
 	size = IVAL(ptr, 2);
-	if (ofs == 0 || size == 0) {
+	if (ofs == 0) {
 		*blob = data_blob(NULL, 0);
 		return NT_STATUS_OK;
 	}
@@ -536,7 +552,7 @@ NTSTATUS smb2_pull_o32s32_blob(struct smb2_request_buffer *buf, TALLOC_CTX *mem_
 	}
 	ofs  = IVAL(ptr, 0);
 	size = IVAL(ptr, 4);
-	if (ofs == 0 || size == 0) {
+	if (ofs == 0) {
 		*blob = data_blob(NULL, 0);
 		return NT_STATUS_OK;
 	}
@@ -563,7 +579,7 @@ NTSTATUS smb2_pull_o16As32_blob(struct smb2_request_buffer *buf, TALLOC_CTX *mem
 	}
 	ofs  = SVAL(ptr, 0);
 	size = IVAL(ptr, 4);
-	if (ofs == 0 || size == 0) {
+	if (ofs == 0) {
 		*blob = data_blob(NULL, 0);
 		return NT_STATUS_OK;
 	}
@@ -587,7 +603,7 @@ NTSTATUS smb2_pull_s32o32_blob(struct smb2_request_buffer *buf, TALLOC_CTX *mem_
 	}
 	size = IVAL(ptr, 0);
 	ofs  = IVAL(ptr, 4);
-	if (ofs == 0 || size == 0) {
+	if (ofs == 0) {
 		*blob = data_blob(NULL, 0);
 		return NT_STATUS_OK;
 	}
@@ -614,11 +630,13 @@ NTSTATUS smb2_pull_o16s16_string(struct smb2_request_buffer *buf, TALLOC_CTX *me
 	status = smb2_pull_o16s16_blob(buf, mem_ctx, ptr, &blob);
 	NT_STATUS_NOT_OK_RETURN(status);
 
+	if (blob.data == NULL) {
+		*str = NULL;
+		return NT_STATUS_OK;
+	}
+
 	if (blob.length == 0) {
-		char *s;
-		s = talloc_strdup(mem_ctx, "");
-		NT_STATUS_HAVE_NO_MEMORY(s);
-		*str = s;
+		*str = talloc_strdup(mem_ctx, "");
 		return NT_STATUS_OK;
 	}
 
@@ -643,7 +661,7 @@ NTSTATUS smb2_push_o16s16_string(struct smb2_request_buffer *buf,
 	NTSTATUS status;
 	ssize_t size;
 
-	if (strcmp("", str) == 0) {
+	if (str == NULL) {
 		return smb2_push_o16s16_blob(buf, ofs, data_blob(NULL, 0));
 	}