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exec: Stop using memory after free

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memory_region_unref(mr) can free memory.

For example I got:

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0x7f43280d4700 (LWP 4462)]
0x00007f43323283c0 in phys_section_destroy (mr=0x7f43259468b0)
at /home/don/xen/tools/qemu-xen-dir/exec.c:1023
1023 if (mr->subpage) {
(gdb) bt
at /home/don/xen/tools/qemu-xen-dir/exec.c:1023
at /home/don/xen/tools/qemu-xen-dir/exec.c:1034
at /home/don/xen/tools/qemu-xen-dir/exec.c:2205
(gdb) p mr
$1 = (MemoryRegion *) 0x7f43259468b0

And this change prevents this.

Backports commit 55b4e80b047300e1512df02887b7448ba3786b62 from qemu
This commit is contained in:
Don Slutz 2018-02-17 19:11:41 -05:00 committed by Lioncash
parent 5218799171
commit 86436964b5
No known key found for this signature in database
GPG key ID: 4E3C3CC1031BA9C7
1 changed files with 3 additions and 1 deletions
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4
qemu/exec.c
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@ -821,9 +821,11 @@ static uint16_t phys_section_add(PhysPageMap *map,
static void phys_section_destroy(MemoryRegion *mr)
{
bool have_sub_page = mr->subpage;
memory_region_unref(mr);
if (mr->subpage) {
if (have_sub_page) {
subpage_t *subpage = container_of(mr, subpage_t, iomem);
object_unref(mr->uc, OBJECT(&subpage->iomem));
g_free(subpage);