linux-kernel - Re: [PATCH v2 01/13] media: v4l2-ctrls-api: fix error handling for v4l2_g

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Message-ID: <20241018082654.04cae950@foz.lan>
Date: Fri, 18 Oct 2024 08:26:54 +0200
From: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
To: Hans Verkuil <hverkuil@...all.nl>
Cc: Ricardo Ribalda <ribalda@...omium.org>, linux-kernel@...r.kernel.org,
 linux-media@...r.kernel.org, stable@...r.kernel.org
Subject: Re: [PATCH v2 01/13] media: v4l2-ctrls-api: fix error handling for
 v4l2_g_ctrl()

Em Fri, 18 Oct 2024 08:13:01 +0200
Hans Verkuil <hverkuil@...all.nl> escreveu:

> On 18/10/2024 07:53, Mauro Carvalho Chehab wrote:
> > As detected by Coverity, the error check logic at get_ctrl() is
> > broken: if ptr_to_user() fails to fill a control due to an error,
> > no errors are returned and v4l2_g_ctrl() returns success on a
> > failed operation, which may cause applications to fail.
> > 
> > Add an error check at get_ctrl() and ensure that it will
> > be returned to userspace without filling the control value if
> > get_ctrl() fails.
> > 
> > Fixes: 71c689dc2e73 ("media: v4l2-ctrls: split up into four source files")
> > Cc: stable@...r.kernel.org
> > Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
> > ---
> >  drivers/media/v4l2-core/v4l2-ctrls-api.c | 16 +++++++++++-----
> >  1 file changed, 11 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/media/v4l2-core/v4l2-ctrls-api.c b/drivers/media/v4l2-core/v4l2-ctrls-api.c
> > index e5a364efd5e6..a0de7eeaf085 100644
> > --- a/drivers/media/v4l2-core/v4l2-ctrls-api.c
> > +++ b/drivers/media/v4l2-core/v4l2-ctrls-api.c
> > @@ -753,9 +753,10 @@ static int get_ctrl(struct v4l2_ctrl *ctrl, struct v4l2_ext_control *c)
> >  		for (i = 0; i < master->ncontrols; i++)
> >  			cur_to_new(master->cluster[i]);
> >  		ret = call_op(master, g_volatile_ctrl);
> > -		new_to_user(c, ctrl);
> > +		if (!ret)
> > +			ret = new_to_user(c, ctrl);
> >  	} else {
> > -		cur_to_user(c, ctrl);
> > +		ret = cur_to_user(c, ctrl);
> >  	}
> >  	v4l2_ctrl_unlock(master);
> >  	return ret;
> > @@ -770,7 +771,10 @@ int v4l2_g_ctrl(struct v4l2_ctrl_handler *hdl, struct v4l2_control *control)
> >  	if (!ctrl || !ctrl->is_int)
> >  		return -EINVAL;
> >  	ret = get_ctrl(ctrl, &c);
> > -	control->value = c.value;
> > +
> > +	if (!ret)
> > +		control->value = c.value;
> > +
> >  	return ret;
> >  }
> >  EXPORT_SYMBOL(v4l2_g_ctrl);
> > @@ -811,10 +815,12 @@ static int set_ctrl_lock(struct v4l2_fh *fh, struct v4l2_ctrl *ctrl,
> >  	int ret;
> >  
> >  	v4l2_ctrl_lock(ctrl);
> > -	user_to_new(c, ctrl);
> > +	ret = user_to_new(c, ctrl);
> > +	if (ret)
> > +		return ret;
> 
> A lock was taken above and that isn't unlocked here.
> 
> It is better to write this as:
> 
> 	if (!ret)
> 		ret = set_ctrl(fh, ctrl, 0);
> 
> >  	ret = set_ctrl(fh, ctrl, 0);
> >  	if (!ret)
> > -		cur_to_user(c, ctrl);
> > +		ret = cur_to_user(c, ctrl);
> >  	v4l2_ctrl_unlock(ctrl);
> >  	return ret;
> >  }

True. See below.

Thanks,
Mauro

-

[PATCH v3] media: v4l2-ctrls-api: fix error handling for v4l2_g_ctrl()

As detected by Coverity, the error check logic at get_ctrl() is
broken: if ptr_to_user() fails to fill a control due to an error,
no errors are returned and v4l2_g_ctrl() returns success on a
failed operation, which may cause applications to fail.

Add an error check at get_ctrl() and ensure that it will
be returned to userspace without filling the control value if
get_ctrl() fails.

Fixes: 71c689dc2e73 ("media: v4l2-ctrls: split up into four source files")
Cc: stable@...r.kernel.org
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@...nel.org>
---
 drivers/media/v4l2-core/v4l2-ctrls-api.c | 17 +++++++++++------
 1 file changed, 11 insertions(+), 6 deletions(-)

diff --git a/drivers/media/v4l2-core/v4l2-ctrls-api.c b/drivers/media/v4l2-core/v4l2-ctrls-api.c
index e5a364efd5e6..95a2202879d8 100644
--- a/drivers/media/v4l2-core/v4l2-ctrls-api.c
+++ b/drivers/media/v4l2-core/v4l2-ctrls-api.c
@@ -753,9 +753,10 @@ static int get_ctrl(struct v4l2_ctrl *ctrl, struct v4l2_ext_control *c)
 		for (i = 0; i < master->ncontrols; i++)
 			cur_to_new(master->cluster[i]);
 		ret = call_op(master, g_volatile_ctrl);
-		new_to_user(c, ctrl);
+		if (!ret)
+			ret = new_to_user(c, ctrl);
 	} else {
-		cur_to_user(c, ctrl);
+		ret = cur_to_user(c, ctrl);
 	}
 	v4l2_ctrl_unlock(master);
 	return ret;
@@ -770,7 +771,10 @@ int v4l2_g_ctrl(struct v4l2_ctrl_handler *hdl, struct v4l2_control *control)
 	if (!ctrl || !ctrl->is_int)
 		return -EINVAL;
 	ret = get_ctrl(ctrl, &c);
-	control->value = c.value;
+
+	if (!ret)
+		control->value = c.value;
+
 	return ret;
 }
 EXPORT_SYMBOL(v4l2_g_ctrl);
@@ -811,10 +815,11 @@ static int set_ctrl_lock(struct v4l2_fh *fh, struct v4l2_ctrl *ctrl,
 	int ret;
 
 	v4l2_ctrl_lock(ctrl);
-	user_to_new(c, ctrl);
-	ret = set_ctrl(fh, ctrl, 0);
+	ret = user_to_new(c, ctrl);
+	if (!ret)
+		ret = set_ctrl(fh, ctrl, 0);
 	if (!ret)
-		cur_to_user(c, ctrl);
+		ret = cur_to_user(c, ctrl);
 	v4l2_ctrl_unlock(ctrl);
 	return ret;
 }
-- 
2.47.0