Hi Arnd,
Thank you for the patch.
On Thu, Mar 18, 2021 at 02:43:18PM +0100, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@xxxxxxxx>
>
> Syzbot found that passing ioctl command 0xc0505609 into a 64-bit
> kernel from a 32-bit process causes uninitialized kernel memory to
> get passed to drivers instead of the user space data:
>
> BUG: KMSAN: uninit-value in check_array_args drivers/media/v4l2-core/v4l2-ioctl.c:3041 [inline]
> BUG: KMSAN: uninit-value in video_usercopy+0x1631/0x3d30 drivers/media/v4l2-core/v4l2-ioctl.c:3315
> CPU: 0 PID: 19595 Comm: syz-executor.4 Not tainted 5.11.0-rc7-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
> __dump_stack lib/dump_stack.c:79 [inline]
> dump_stack+0x21c/0x280 lib/dump_stack.c:120
> kmsan_report+0xfb/0x1e0 mm/kmsan/kmsan_report.c:118
> __msan_warning+0x5f/0xa0 mm/kmsan/kmsan_instr.c:197
> check_array_args drivers/media/v4l2-core/v4l2-ioctl.c:3041 [inline]
> video_usercopy+0x1631/0x3d30 drivers/media/v4l2-core/v4l2-ioctl.c:3315
> video_ioctl2+0x9f/0xb0 drivers/media/v4l2-core/v4l2-ioctl.c:3391
> v4l2_ioctl+0x255/0x290 drivers/media/v4l2-core/v4l2-dev.c:360
> v4l2_compat_ioctl32+0x2c6/0x370 drivers/media/v4l2-core/v4l2-compat-ioctl32.c:1248
> __do_compat_sys_ioctl fs/ioctl.c:842 [inline]
> __se_compat_sys_ioctl+0x53d/0x1100 fs/ioctl.c:793
> __ia32_compat_sys_ioctl+0x4a/0x70 fs/ioctl.c:793
> do_syscall_32_irqs_on arch/x86/entry/common.c:79 [inline]
> __do_fast_syscall_32+0x102/0x160 arch/x86/entry/common.c:141
> do_fast_syscall_32+0x6a/0xc0 arch/x86/entry/common.c:166
> do_SYSENTER_32+0x73/0x90 arch/x86/entry/common.c:209
> entry_SYSENTER_compat_after_hwframe+0x4d/0x5c
>
> The time32 commands are defined but were never meant to be called on
> 64-bit machines, as those have always used time64 interfaces. I missed
> this in my patch that introduced the time64 handling on 32-bit platforms.
>
> The problem in this case is the mismatch of one function checking for
> the numeric value of the command and another function checking for the
> type of process (native vs compat) instead, with the result being that
> for this combination, nothing gets copied into the buffer at all.
>
> Avoid this by only trying to convert the time32 commands when running
> on a 32-bit kernel where these are defined in a meaningful way.
>
> Fixes: 577c89b0ce72 ("media: v4l2-core: fix v4l2_buffer handling for time64 ABI")
> Reported-by: syzbot+142888ffec98ab194028@xxxxxxxxxxxxxxxxxxxxxxxxx
> Tested-by: Hans Verkuil <hverkuil-cisco@xxxxxxxxx>
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
v4l2_event vs. v4l2_event32 vs. v4l2_event_time32 vs.
v4l2_event32_time32 is a bit confusing. Do I understand correctly that
the code below runs for the non-compat path, thus native userspace
(32-bit on 32-bit machines, 64-bit on 64-bit machines), and handles the
case of a native userspace using a 32-bit time ? If so it indeed doesn't
make sense for 64-bit machines.
Reviewed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> ---
> This patch adds two more changes than the version that Hans tested
> ---
> drivers/media/v4l2-core/v4l2-ioctl.c | 6 +++---
> drivers/media/v4l2-core/v4l2-subdev.c | 2 +-
> 2 files changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
> index 31d1342e61e8..2b1bb68dc27f 100644
> --- a/drivers/media/v4l2-core/v4l2-ioctl.c
> +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
> @@ -3115,7 +3115,7 @@ static int check_array_args(unsigned int cmd, void *parg, size_t *array_size,
> static unsigned int video_translate_cmd(unsigned int cmd)
> {
> switch (cmd) {
> -#ifdef CONFIG_COMPAT_32BIT_TIME
> +#if !defined(CONFIG_64BIT) && defined(CONFIG_COMPAT_32BIT_TIME)
> case VIDIOC_DQEVENT_TIME32:
> return VIDIOC_DQEVENT;
> case VIDIOC_QUERYBUF_TIME32:
> @@ -3169,7 +3169,7 @@ static int video_get_user(void __user *arg, void *parg,
> err = v4l2_compat_get_user(arg, parg, cmd);
> } else {
> switch (cmd) {
> -#ifdef CONFIG_COMPAT_32BIT_TIME
> +#if !defined(CONFIG_64BIT) && defined(CONFIG_COMPAT_32BIT_TIME)
> case VIDIOC_QUERYBUF_TIME32:
> case VIDIOC_QBUF_TIME32:
> case VIDIOC_DQBUF_TIME32:
> @@ -3224,7 +3224,7 @@ static int video_put_user(void __user *arg, void *parg,
> return v4l2_compat_put_user(arg, parg, cmd);
>
> switch (cmd) {
> -#ifdef CONFIG_COMPAT_32BIT_TIME
> +#if !defined(CONFIG_64BIT) && defined(CONFIG_COMPAT_32BIT_TIME)
> case VIDIOC_DQEVENT_TIME32: {
> struct v4l2_event *ev = parg;
> struct v4l2_event_time32 ev32;
> diff --git a/drivers/media/v4l2-core/v4l2-subdev.c b/drivers/media/v4l2-core/v4l2-subdev.c
> index 336133dbc759..9f5573d3b857 100644
> --- a/drivers/media/v4l2-core/v4l2-subdev.c
> +++ b/drivers/media/v4l2-core/v4l2-subdev.c
> @@ -428,7 +428,7 @@ static long subdev_do_ioctl(struct file *file, unsigned int cmd, void *arg)
>
> return v4l2_event_dequeue(vfh, arg, file->f_flags & O_NONBLOCK);
>
> -#ifdef CONFIG_COMPAT_32BIT_TIME
> +#if !defined(CONFIG_64BIT) && defined(CONFIG_COMPAT_32BIT_TIME)
> case VIDIOC_DQEVENT_TIME32: {
> struct v4l2_event_time32 *ev32 = arg;
> struct v4l2_event ev = { };
--
Regards,
Laurent Pinchart
