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media: v4l2-core: explicitly clear ioctl input data

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As seen from a recent syzbot bug report, mistakes in the compat ioctl
implementation can lead to uninitialized kernel stack data getting used
as input for driver ioctl handlers.

The reported bug is now fixed, but it's possible that other related
bugs are still present or get added in the future. As the drivers need
to check user input already, the possible impact is fairly low, but it
might still cause an information leak.

To be on the safe side, always clear the entire ioctl buffer before
calling the conversion handler functions that are meant to initialize
them.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
This commit is contained in:
Arnd Bergmann 2021-06-14 12:34:03 +02:00 committed by Mauro Carvalho Chehab
parent c344f07aa1
commit 7b53cca764
1 changed files with 2 additions and 0 deletions
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2
drivers/media/v4l2-core/v4l2-ioctl.c
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@ -3124,8 +3124,10 @@ static int video_get_user(void __user *arg, void *parg,
if (copy_from_user(parg, (void __user *)arg, n))
err = -EFAULT;
} else if (in_compat_syscall()) {
memset(parg, 0, n);
err = v4l2_compat_get_user(arg, parg, cmd);
} else {
memset(parg, 0, n);
#if !defined(CONFIG_64BIT) && defined(CONFIG_COMPAT_32BIT_TIME)
switch (cmd) {
case VIDIOC_QUERYBUF_TIME32: