qemu: fix CVE-2021-20196 block fdc null pointer dereference may lead to guest crash

Upstream-Status: Backport [https://gitlab.com/qemu-project/qemu/-/commit/1ab95af033a419e7a64e2d58e67dd96b20af5233]

(From OE-Core rev: 1523fcbb6fef60d30c07377673fca265c5c9781c)

Signed-off-by: Vivek Kumbhar <vkumbhar@mvista.com>
Signed-off-by: Steve Sakoman <steve@sakoman.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

2 files changed, 63 insertions, 0 deletions

diff --git a/meta/recipes-devtools/qemu/qemu.inc b/meta/recipes-devtools/qemu/qemu.inc
index 764f948a28..a915b54c1a 100644
--- a/meta/recipes-devtools/qemu/qemu.inc
+++ b/meta/recipes-devtools/qemu/qemu.inc
@@ -113,6 +113,7 @@ SRC_URI = "https://download.qemu.org/${BPN}-${PV}.tar.xz \
            file://CVE-2022-0216-2.patch \
            file://CVE-2021-3750.patch \
            file://CVE-2021-3638.patch \
+           file://CVE-2021-20196.patch \
            "
 UPSTREAM_CHECK_REGEX = "qemu-(?P<pver>\d+(\.\d+)+)\.tar"
 
diff --git a/meta/recipes-devtools/qemu/qemu/CVE-2021-20196.patch b/meta/recipes-devtools/qemu/qemu/CVE-2021-20196.patch
new file mode 100644
index 0000000000..e9b815740f
--- /dev/null
+++ b/meta/recipes-devtools/qemu/qemu/CVE-2021-20196.patch
@@ -0,0 +1,62 @@
+From 94608c59045791dfd35102bc59b792e96f2cfa30 Mon Sep 17 00:00:00 2001
+From: Vivek Kumbhar <vkumbhar@mvista.com>
+Date: Tue, 29 Nov 2022 15:57:13 +0530
+Subject: [PATCH] CVE-2021-20196
+
+Upstream-Status: Backport [https://gitlab.com/qemu-project/qemu/-/commit/1ab95af033a419e7a64e2d58e67dd96b20af5233]
+CVE: CVE-2021-20196
+Signed-off-by: Vivek Kumbhar <vkumbhar@mvista.com>
+
+hw/block/fdc: Kludge missing floppy drive to fix CVE-2021-20196
+
+Guest might select another drive on the bus by setting the
+DRIVE_SEL bit of the DIGITAL OUTPUT REGISTER (DOR).
+The current controller model doesn't expect a BlockBackend
+to be NULL. A simple way to fix CVE-2021-20196 is to create
+an empty BlockBackend when it is missing. All further
+accesses will be safely handled, and the controller state
+machines keep behaving correctly.
+---
+ hw/block/fdc.c | 19 ++++++++++++++++++-
+ 1 file changed, 18 insertions(+), 1 deletion(-)
+
+diff --git a/hw/block/fdc.c b/hw/block/fdc.c
+index ac5d31e8..e128e975 100644
+--- a/hw/block/fdc.c
++++ b/hw/block/fdc.c
+@@ -58,6 +58,11 @@
+         }                                                       \
+     } 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                                      */
+@@ -1356,7 +1361,19 @@ 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) */
+-- 
+2.25.1
+