Merge tag 'ide-pull-request' of https://gitlab.com/jsnow/qemu into staging

Pull request

# gpg: Signature made Wed 01 Dec 2021 10:17:38 PM PST
# gpg:                using RSA key F9B7ABDBBCACDF95BE76CBD07DEF8106AAFC390E
# gpg: Good signature from "John Snow (John Huston) <jsnow@redhat.com>" [full]

* tag 'ide-pull-request' of https://gitlab.com/jsnow/qemu:
  tests/qtest/fdc-test: Add a regression test for CVE-2021-20196
  hw/block/fdc: Kludge missing floppy drive to fix CVE-2021-20196
  hw/block/fdc: Extract blk_create_empty_drive()

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>

1 files changed, 20 insertions, 3 deletions

diff --git a/hw/block/fdc.c b/hw/block/fdc.c
index fa933cd326..21d18ac2e3 100644
--- a/hw/block/fdc.c
+++ b/hw/block/fdc.c
@@ -61,6 +61,12 @@
     } while (0)
 
 
+/* Anonymous BlockBackend for empty drive */
+static BlockBackend *blk_create_empty_drive(void)
+{
+    return blk_new(qemu_get_aio_context(), 0, BLK_PERM_ALL);
+}
+
 /********************************************************/
 /* qdev floppy bus                                      */
 
@@ -486,8 +492,7 @@ static void floppy_drive_realize(DeviceState *qdev, Error **errp)
     }
 
     if (!dev->conf.blk) {
-        /* Anonymous BlockBackend for an empty drive */
-        dev->conf.blk = blk_new(qemu_get_aio_context(), 0, BLK_PERM_ALL);
+        dev->conf.blk = blk_create_empty_drive();
         ret = blk_attach_dev(dev->conf.blk, qdev);
         assert(ret == 0);
 
@@ -1161,7 +1166,19 @@ static FDrive *get_drv(FDCtrl *fdctrl, int unit)
 
 static FDrive *get_cur_drv(FDCtrl *fdctrl)
 {
-    return get_drv(fdctrl, fdctrl->cur_drv);
+    FDrive *cur_drv = get_drv(fdctrl, fdctrl->cur_drv);
+
+    if (!cur_drv->blk) {
+        /*
+         * Kludge: empty drive line selected. Create an anonymous
+         * BlockBackend to avoid NULL deref with various BlockBackend
+         * API calls within this model (CVE-2021-20196).
+         * Due to the controller QOM model limitations, we don't
+         * attach the created to the controller device.
+         */
+        cur_drv->blk = blk_create_empty_drive();
+    }
+    return cur_drv;
 }
 
 /* Status A register : 0x00 (read-only) */