[PATCH-for-5.0 v2 1/4] Revert "prevent crash when executing guest-file-read with large count"

["Philippe Mathieu-Daudé" <philmd@redhat.com>]

By using g_try_malloc() instead of g_malloc() the qemu-guest-agent
Denial-of-Service attack referred in commit 807e2b6fce is reduced,
but still triggerable:

  - bisect file size S until g_try_malloc(S) fails,
  - use S - 1:
    g_try_malloc(S - 1) succeeds, but g_new0() few lines later will
    fail.

 346     buf = g_try_malloc0(count + 1);
 347     if (!buf) {
 348         error_setg(errp,
 349                    "failed to allocate sufficient memory "
 350                    "to complete the requested service");
 351         return NULL;
 352     }
 353     is_ok = ReadFile(fh, buf, count, &read_count, NULL);
 354     if (!is_ok) {
 355         error_setg_win32(errp, GetLastError(), "failed to read file");
 356         slog("guest-file-read failed, handle %" PRId64, handle);
 357     } else {
 358         buf[read_count] = 0;
 359         read_data = g_new0(GuestFileRead, 1);
                         ^^^^^^

Instead we are going to put a low hard limit on 'count' in the next
commits.
This reverts commit 807e2b6fce022707418bc8f61c069d91c613b3d2.

Suggested-by: Daniel P. Berrangé <berrange@redhat.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
 qga/commands-win32.c | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/qga/commands-win32.c b/qga/commands-win32.c
index b49920e201..46cea7d1d9 100644
--- a/qga/commands-win32.c
+++ b/qga/commands-win32.c
@@ -343,13 +343,7 @@ GuestFileRead *qmp_guest_file_read(int64_t handle, bool has_count,
     }
 
     fh = gfh->fh;
-    buf = g_try_malloc0(count + 1);
-    if (!buf) {
-        error_setg(errp,
-                   "failed to allocate sufficient memory "
-                   "to complete the requested service");
-        return NULL;
-    }
+    buf = g_malloc0(count + 1);
     is_ok = ReadFile(fh, buf, count, &read_count, NULL);
     if (!is_ok) {
         error_setg_win32(errp, GetLastError(), "failed to read file");
-- 
2.21.1