[PATCH v3] exec: set map length to zero when returning NULL

[P J P <ppandit@redhat.com>]

From: Prasad J Pandit <pjp@fedoraproject.org>

When mapping physical memory into host's virtual address space,
'address_space_map' may return NULL if BounceBuffer is in_use.
Set and return '*plen = 0' to avoid later NULL pointer dereference.

Reported-by: Alexander Bulekov <alxndr@bu.edu>
Fixes: https://bugs.launchpad.net/qemu/+bug/1878259
Signed-off-by: Prasad J Pandit <pjp@fedoraproject.org>
---
 exec.c | 1 +
 1 file changed, 1 insertion(+)

Update v3: set *plen = 0;
  -> https://lists.gnu.org/archive/html/qemu-devel/2020-05/msg06249.html

diff --git a/exec.c b/exec.c
index 5162f0d12f..4eea84bf66 100644
--- a/exec.c
+++ b/exec.c
@@ -3538,6 +3538,7 @@ void *address_space_map(AddressSpace *as,
 
     if (!memory_access_is_direct(mr, is_write)) {
         if (atomic_xchg(&bounce.in_use, true)) {
+            *plen = 0;
             return NULL;
         }
         /* Avoid unbounded allocations */
-- 
2.26.2