[PATCH 2/2] hw/nvme: Avoid dynamic stack allocation

[Peter Maydell <peter.maydell@linaro.org>]

Instead of using a variable-length array in nvme_map_prp(),
allocate on the stack with a g_autofree pointer.

The codebase has very few VLAs, and if we can get rid of them all we
can make the compiler error on new additions.  This is a defensive
measure against security bugs where an on-stack dynamic allocation
isn't correctly size-checked (e.g.  CVE-2021-3527).

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
---
Using the approach suggested by RTH in review of Philippe's
original patch:
 https://patchew.org/QEMU/20210505211047.1496765-1-philmd@redhat.com/20210505211047.1496765-9-philmd@redhat.com/
---
 hw/nvme/ctrl.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/hw/nvme/ctrl.c b/hw/nvme/ctrl.c
index d99a6f5c9a2..90687b168ae 100644
--- a/hw/nvme/ctrl.c
+++ b/hw/nvme/ctrl.c
@@ -894,7 +894,7 @@ static uint16_t nvme_map_prp(NvmeCtrl *n, NvmeSg *sg, uint64_t prp1,
     len -= trans_len;
     if (len) {
         if (len > n->page_size) {
-            uint64_t prp_list[n->max_prp_ents];
+            g_autofree uint64_t *prp_list = g_new(uint64_t, n->max_prp_ents);
             uint32_t nents, prp_trans;
             int i = 0;
 
-- 
2.34.1