Re: [PATCH v3 1/8] media: v4l2-core: ignore native time32 ioctls on 64-bit

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Arnd,

Thank you for the patch.

On Mon, Jun 14, 2021 at 12:34:02PM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@arndb.de>
> 
> 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@syzkaller.appspotmail.com
> Tested-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
> This patch adds two more changes than the version that Hans tested
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

> ---
>  drivers/media/v4l2-core/v4l2-ioctl.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
> index 2673f51aafa4..58df927aec7e 100644
> --- a/drivers/media/v4l2-core/v4l2-ioctl.c
> +++ b/drivers/media/v4l2-core/v4l2-ioctl.c
> @@ -3073,7 +3073,7 @@ 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:
> @@ -3127,7 +3127,7 @@ 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:
> @@ -3182,7 +3182,7 @@ 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;

-- 
Regards,

Laurent Pinchart