[PATCH 3/5] Xephyr: integer overflow in ephyrHostGLXGetStringFromServer()

[Alan Coopersmith]

reply.length & reply.size are CARD32s and need to be bounds checked before
multiplying or adding to come up with the total size to allocate, to avoid
integer overflow leading to underallocation and writing data from the
network past the end of the allocated buffer.

Reported-by: Ilja Van Sprundel <ivansprundel at ioactive.com>
Signed-off-by: Alan Coopersmith <alan.coopersmith at oracle.com>
---
 hw/kdrive/ephyr/ephyrhostglx.c |   40 +++++++++++++++++++++++-----------------
 1 file changed, 23 insertions(+), 17 deletions(-)

diff --git a/hw/kdrive/ephyr/ephyrhostglx.c b/hw/kdrive/ephyr/ephyrhostglx.c
index 5c6c40f..2327fc0 100644
--- a/hw/kdrive/ephyr/ephyrhostglx.c
+++ b/hw/kdrive/ephyr/ephyrhostglx.c
@@ -169,7 +169,8 @@ ephyrHostGLXGetStringFromServer(int a_screen_number,
     int default_screen = DefaultScreen(dpy);
     xGLXGenericGetStringReq *req = NULL;
     xGLXSingleReply reply;
-    int length = 0, numbytes = 0, major_opcode = 0, get_string_op = 0;
+    unsigned long length = 0, numbytes = 0;
+    int major_opcode = 0, get_string_op = 0;
 
     EPHYR_RETURN_VAL_IF_FAIL(dpy && a_string, FALSE);
 
@@ -209,36 +210,41 @@ ephyrHostGLXGetStringFromServer(int a_screen_number,
 
     _XReply(dpy, (xReply *) &reply, 0, False);
 
-    length = reply.length * 4;
-    if (!length) {
-        numbytes = 0;
-    }
-    else {
+#if UINT32_MAX >= (ULONG_MAX / 4)
+    if (reply.length >= (ULONG_MAX / 4))
+        goto eat_out;
+#endif
+    if (reply.length > 0) {
+        length = (unsigned long) reply.length * 4;
         numbytes = reply.size;
     }
     EPHYR_LOG("going to get a string of size:%d\n", numbytes);
 
-    *a_string = (char *) Xmalloc(numbytes + 1);
-    if (!a_string) {
+    if (numbytes < INT_MAX)
+        *a_string = Xcalloc(numbytes + 1, 1);
+    else
+        *a_string = NULL;
+    if (*a_string == NULL) {
         EPHYR_LOG_ERROR("allocation failed\n");
-        goto out;
+        goto eat_out;
     }
 
-    memset(*a_string, 0, numbytes + 1);
     if (_XRead(dpy, *a_string, numbytes)) {
-        UnlockDisplay(dpy);
-        SyncHandle();
         EPHYR_LOG_ERROR("read failed\n");
-        goto out;
+        length = 0; /* if read failed, no idea how much to eat */
+    }
+    else {
+        length -= numbytes;
+        EPHYR_LOG("strname:%#x, strvalue:'%s', strlen:%d\n",
+                  a_string_name, *a_string, numbytes);
+        is_ok = TRUE;
     }
-    length -= numbytes;
+
+ eat_out:
     _XEatData(dpy, length);
     UnlockDisplay(dpy);
     SyncHandle();
-    EPHYR_LOG("strname:%#x, strvalue:'%s', strlen:%d\n",
-              a_string_name, *a_string, numbytes);
 
-    is_ok = TRUE;
  out:
     EPHYR_LOG("leave\n");
     return is_ok;
-- 
1.7.9.2