[PATCH-for-6.2 v2 1/2] hw/nvme/ctrl: Fix buffer overrun in nvme_changed_nslist (CVE-2021-3947)

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

Both 'buf_len' and 'off' arguments are under guest control.
Since nvme_c2h() doesn't check out of boundary access, the
caller must check for eventual buffer overrun on 'trans_len'.

Cc: qemu-stable@nongnu.org
Reported-by: Qiuhao Li <Qiuhao.Li@outlook.com>
Fixes: f432fdfa121 ("support changed namespace asynchronous event")
Signed-off-by: Philippe Mathieu-Daudé <philmd@redhat.com>
---
 hw/nvme/ctrl.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/hw/nvme/ctrl.c b/hw/nvme/ctrl.c
index 6a571d18cfa..93a24464647 100644
--- a/hw/nvme/ctrl.c
+++ b/hw/nvme/ctrl.c
@@ -4168,8 +4168,11 @@ static uint16_t nvme_changed_nslist(NvmeCtrl *n, uint8_t rae, uint32_t buf_len,
     int i = 0;
     uint32_t nsid;
 
-    memset(nslist, 0x0, sizeof(nslist));
     trans_len = MIN(sizeof(nslist) - off, buf_len);
+    if (trans_len >= sizeof(nslist)) {
+        return NVME_INVALID_FIELD | NVME_DNR;
+    }
+    memset(nslist, 0x0, sizeof(nslist));
 
     while ((nsid = find_first_bit(n->changed_nsids, NVME_CHANGED_NSID_SIZE)) !=
             NVME_CHANGED_NSID_SIZE) {
-- 
2.31.1