From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
From: Frediano Ziglio <fziglio@redhat.com>
Date: Wed, 27 Jun 2018 10:55:05 +0100
Subject: [PATCH spice-common] canvas_base: Check for overflows decoding LZ4

Check that we have enough data before reading.
This could lead to read buffer overflows being undetected.
This is not a security issue, read happens only in the client not causing
any information leakage, maximum can generate a crash or some garbage on
the screen.

Signed-off-by: Frediano Ziglio <fziglio@redhat.com>
Acked-by: Jonathon Jongsma <jjongsma@redhat.com>
---
 common/canvas_base.c | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/spice-common/common/canvas_base.c b/spice-common/common/canvas_base.c
index 2fd60aa..3283e88 100644
--- a/spice-common/common/canvas_base.c
+++ b/spice-common/common/canvas_base.c
@@ -537,6 +537,10 @@ static pixman_image_t *canvas_get_lz4(CanvasBase *canvas, SpiceImage *image)
     width = image->descriptor.width;
     stride_encoded = width;
     height = image->descriptor.height;
+    if (data + 2 > data_end) {
+        g_warning("missing header in LZ4 data");
+        return NULL;
+    }
     top_down = *(data++);
     spice_format = *(data++);
     switch (spice_format) {
@@ -579,16 +583,22 @@ static pixman_image_t *canvas_get_lz4(CanvasBase *canvas, SpiceImage *image)
     bits = dest;
 
     do {
+        if (data + 4 > data_end) {
+            goto format_error;
+        }
         // Read next compressed block
         enc_size = ntohl(*SPICE_UNALIGNED_CAST(uint32_t *, data));
         data += 4;
+        /* check overflow. This check is a bit different to avoid
+         * possible overflows. From previous check data_end - data cannot overflow.
+         * Computing data + enc_size on 32 bit could cause overflows. */
+        if (enc_size < 0 || data_end - data < (unsigned int) enc_size) {
+            goto format_error;
+        }
         dec_size = LZ4_decompress_safe_continue(stream, (const char *) data,
                                                 (char *) dest, enc_size, available);
         if (dec_size <= 0) {
-            spice_warning("Error decoding LZ4 block\n");
-            pixman_image_unref(surface);
-            surface = NULL;
-            break;
+            goto format_error;
         }
         dest += dec_size;
         available -= dec_size;
@@ -599,6 +609,12 @@ static pixman_image_t *canvas_get_lz4(CanvasBase *canvas, SpiceImage *image)
 
     LZ4_freeStreamDecode(stream);
     return surface;
+
+format_error:
+    spice_warning("Error decoding LZ4 block\n");
+    LZ4_freeStreamDecode(stream);
+    pixman_image_unref(surface);
+    return NULL;
 }
 #endif