[glib] gio: Prevent hang writing to a large GMemoryBuffer

[Ross Lagerwall <rossl src gnome org>]

commit 226c292b6ab95014648e9fc0a082bb6c26eeccc8
Author: Ross Lagerwall <rosslagerwall gmail com>
Date:   Wed Oct 29 22:12:39 2014 +0000

    gio: Prevent hang writing to a large GMemoryBuffer
    
    Fix a hang due to overflow by using unsigned numbers and explicitly
    checking if the number overflows to zero.  This also fixes the previous
    logic which assigned an int which may be negative to an unsigned number
    resulting in sign extension and strange results.
    
    Use gsize rather than int to allow for large buffers on 64 bit machines.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=727988

 gio/gdbusmessage.c |   18 ++++++++----------
 1 files changed, 8 insertions(+), 10 deletions(-)
---
diff --git a/gio/gdbusmessage.c b/gio/gdbusmessage.c
index 5ad8694..766609e 100644
--- a/gio/gdbusmessage.c
+++ b/gio/gdbusmessage.c
@@ -204,12 +204,12 @@ g_memory_buffer_read_uint64 (GMemoryBuffer  *mbuf)
 
 #define MIN_ARRAY_SIZE  128
 
-static gint
-g_nearest_pow (gint num)
+static gsize
+g_nearest_pow (gsize num)
 {
-  gint n = 1;
+  gsize n = 1;
 
-  while (n < num)
+  while (n < num && n > 0)
     n <<= 1;
 
   return n;
@@ -261,12 +261,10 @@ g_memory_buffer_write (GMemoryBuffer  *mbuf,
          TODO: This wastes a lot of memory at large buffer sizes.
                Figure out a more rational allocation strategy. */
       new_size = g_nearest_pow (mbuf->pos + count);
-      /* Check for overflow again. We have only checked if
-         pos + count > G_MAXSIZE, but it only catches the case of writing
-         more than 4GiB total on a 32-bit system. There's still the problem
-         of g_nearest_pow overflowing above 0x7fffffff, so we're
-         effectively limited to 2GiB. */
-      if (new_size < mbuf->len)
+      /* Check for overflow again. We have checked if
+         pos + count > G_MAXSIZE, but now check if g_nearest_pow () has
+         overflowed */
+      if (new_size == 0)
         return FALSE;
 
       new_size = MAX (new_size, MIN_ARRAY_SIZE);