exec: Fix bounce buffer allocation in address_space_map()

This fixes a regression introduced by commit e3127ae0c, which kept the
allocation size of the bounce buffer limited to one page in order to
avoid unbounded allocations (as explained in the commit message of
6d16c2f88), but broke the reporting of the shortened bounce buffer to
the caller. The caller therefore assumes that the full requested size
was provided and causes memory corruption when writing beyond the end of
the actually allocated buffer.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/exec.c b/exec.c
index 2e31ffcb2c..b453713bdb 100644
--- a/exec.c
+++ b/exec.c
@@ -2099,7 +2099,9 @@ void *address_space_map(AddressSpace *as,
         if (bounce.buffer) {
             return NULL;
         }
-        bounce.buffer = qemu_memalign(TARGET_PAGE_SIZE, TARGET_PAGE_SIZE);
+        /* Avoid unbounded allocations */
+        l = MIN(l, TARGET_PAGE_SIZE);
+        bounce.buffer = qemu_memalign(TARGET_PAGE_SIZE, l);
         bounce.addr = addr;
         bounce.len = l;