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

1 files changed, 8 insertions, 10 deletions

diff --git a/gio/gdbusmessage.c b/gio/gdbusmessage.c
index 5ad86940f..766609ec8 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);