On Tue, Jul 18, 2023 at 02:58:46PM +0200, Ard Biesheuvel wrote:

...

-static int deflate_comp_init(struct deflate_ctx *ctx)
+static int deflate_process(struct acomp_req *req, struct z_stream_s *stream,
+			   int (*process)(struct z_stream_s *, int))
 {
-	int ret = 0;
-	struct z_stream_s *stream = &ctx->comp_stream;
+	unsigned int slen = req->slen;
+	unsigned int dlen = req->dlen;
+	struct scatter_walk src, dst;
+	unsigned int scur, dcur;
+	int ret;
 
-	stream->workspace = vzalloc(zlib_deflate_workspacesize(
-				-DEFLATE_DEF_WINBITS, DEFLATE_DEF_MEMLEVEL));
-	if (!stream->workspace) {
-		ret = -ENOMEM;
-		goto out;
-	}
+	stream->avail_in = stream->avail_out = 0;
+
+	scatterwalk_start(&src, req->src);
+	scatterwalk_start(&dst, req->dst);
+
+	scur = dcur = 0;
+
+	do {
+		if (stream->avail_in == 0) {
+			if (scur) {
+				slen -= scur;
+
+				scatterwalk_unmap(stream->next_in - scur);
+				scatterwalk_advance(&src, scur);
+				scatterwalk_done(&src, 0, slen);
+			}
+
+			scur = scatterwalk_clamp(&src, slen);
+			if (scur) {
+				stream->next_in = scatterwalk_map(&src);
+				stream->avail_in = scur;
+			}
+		}
+
+		if (stream->avail_out == 0) {
+			if (dcur) {
+				dlen -= dcur;
+
+				scatterwalk_unmap(stream->next_out - dcur);
+				scatterwalk_advance(&dst, dcur);
+				scatterwalk_done(&dst, 1, dlen);
+			}
+
+			dcur = scatterwalk_clamp(&dst, dlen);
+			if (!dcur)
+				break;

Hi Ard,

I'm unsure if this can happen. But if this break occurs in the first
iteration of this do loop, then ret will be used uninitialised below.

Smatch noticed this.

+
+			stream->next_out = scatterwalk_map(&dst);
+			stream->avail_out = dcur;
+		}
+
+		ret = process(stream, (slen == scur) ? Z_FINISH : Z_SYNC_FLUSH);
+	} while (ret == Z_OK);
+
+	if (scur)
+		scatterwalk_unmap(stream->next_in - scur);
+	if (dcur)
+		scatterwalk_unmap(stream->next_out - dcur);
+
+	if (ret != Z_STREAM_END)
+		return -EINVAL;
+
+	req->dlen = stream->total_out;
+	return 0;
+}

...