media: v4l2: prepare compat-ioctl rework

The v4l2-compat-ioctl32() currently takes an extra round trip through user
space pointers when converting the data structure formats. In particular,
this involves using the compat_alloc_user_space() and copy_in_user()
helpers that often lead to worse compat handlers compared to using
in_compat_syscall() checks when copying the data.

The native implementation already gained a simpler method to deal with
the conversion for the time32 conversion.  Hook into the same places to
provide a location for reading and writing user space data from inside
of the generic video_usercopy() helper.

Hans Verkuil rewrote the video_get_user() function here to simplify
the zeroing of the extra input fields and fixed a couple of bugs in
the original implementation.

[hverkuil: fix: CHECK: Please don't use multiple blank lines]
Co-developed-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>

drivers/media/v4l2-core/v4l2-compat-ioctl32.c

@@ -1414,6 +1414,59 @@ static int put_v4l2_edid32(struct v4l2_edid __user *p64,
 #define VIDIOC_G_OUTPUT32	_IOR ('V', 46, s32)
 #define VIDIOC_S_OUTPUT32	_IOWR('V', 47, s32)
 
+unsigned int v4l2_compat_translate_cmd(unsigned int cmd)
+{
+	switch (cmd) {
+	}
+	return cmd;
+}
+
+int v4l2_compat_get_user(void __user *arg, void *parg, unsigned int cmd)
+{
+	switch (cmd) {
+	}
+	return 0;
+}
+
+int v4l2_compat_put_user(void __user *arg, void *parg, unsigned int cmd)
+{
+	switch (cmd) {
+	}
+	return 0;
+}
+
+int v4l2_compat_get_array_args(struct file *file, void *mbuf,
+			       void __user *user_ptr, size_t array_size,
+			       unsigned int cmd, void *arg)
+{
+	int err = 0;
+
+	switch (cmd) {
+	default:
+		if (copy_from_user(mbuf, user_ptr, array_size))
+			err = -EFAULT;
+		break;
+	}
+
+	return err;
+}
+
+int v4l2_compat_put_array_args(struct file *file, void __user *user_ptr,
+			       void *mbuf, size_t array_size,
+			       unsigned int cmd, void *arg)
+{
+	int err = 0;
+
+	switch (cmd) {
+	default:
+		if (copy_to_user(user_ptr, mbuf, array_size))
+			err = -EFAULT;
+		break;
+	}
+
+	return err;
+}
+
 /**
  * alloc_userspace() - Allocates a 64-bits userspace pointer compatible
  *	for calling the native 64-bits version of an ioctl.

drivers/media/v4l2-core/v4l2-ioctl.c

@@ -8,6 +8,7 @@
  *              Mauro Carvalho Chehab <mchehab@kernel.org> (version 2)
  */
 
+#include <linux/compat.h>
 #include <linux/mm.h>
 #include <linux/module.h>
 #include <linux/slab.h>
@@ -3104,14 +3105,18 @@ static unsigned int video_translate_cmd(unsigned int cmd)
 		return VIDIOC_PREPARE_BUF;
 #endif
 	}
+	if (in_compat_syscall())
+		return v4l2_compat_translate_cmd(cmd);
 
 	return cmd;
 }
 
-static int video_get_user(void __user *arg, void *parg, unsigned int cmd,
+static int video_get_user(void __user *arg, void *parg,
+			  unsigned int real_cmd, unsigned int cmd,
 			  bool *always_copy)
 {
-	unsigned int n = _IOC_SIZE(cmd);
+	unsigned int n = _IOC_SIZE(real_cmd);
+	int err = 0;
 
 	if (!(_IOC_DIR(cmd) & _IOC_WRITE)) {
 		/* read-only ioctl */
@@ -3119,6 +3124,27 @@ static int video_get_user(void __user *arg, void *parg, unsigned int cmd,
 		return 0;
 	}
 
+	/*
+	 * In some cases, only a few fields are used as input,
+	 * i.e. when the app sets "index" and then the driver
+	 * fills in the rest of the structure for the thing
+	 * with that index.  We only need to copy up the first
+	 * non-input field.
+	 */
+	if (v4l2_is_known_ioctl(real_cmd)) {
+		u32 flags = v4l2_ioctls[_IOC_NR(real_cmd)].flags;
+
+		if (flags & INFO_FL_CLEAR_MASK)
+			n = (flags & INFO_FL_CLEAR_MASK) >> 16;
+		*always_copy = flags & INFO_FL_ALWAYS_COPY;
+	}
+
+	if (cmd == real_cmd) {
+		if (copy_from_user(parg, (void __user *)arg, n))
+			err = -EFAULT;
+	} else if (in_compat_syscall()) {
+		err = v4l2_compat_get_user(arg, parg, cmd);
+	} else {
 		switch (cmd) {
 #ifdef CONFIG_COMPAT_32BIT_TIME
 		case VIDIOC_QUERYBUF_TIME32:
@@ -3146,46 +3172,34 @@ static int video_get_user(void __user *arg, void *parg, unsigned int cmd,
 					.length		= vb32.length,
 					.request_fd	= vb32.request_fd,
 			};
-
-		if (cmd == VIDIOC_QUERYBUF_TIME32)
-			vb->request_fd = 0;
-
 			break;
 		}
 #endif
-	default:
-		/*
-		 * In some cases, only a few fields are used as input,
-		 * i.e. when the app sets "index" and then the driver
-		 * fills in the rest of the structure for the thing
-		 * with that index.  We only need to copy up the first
-		 * non-input field.
-		 */
-		if (v4l2_is_known_ioctl(cmd)) {
-			u32 flags = v4l2_ioctls[_IOC_NR(cmd)].flags;
-
-			if (flags & INFO_FL_CLEAR_MASK)
-				n = (flags & INFO_FL_CLEAR_MASK) >> 16;
-			*always_copy = flags & INFO_FL_ALWAYS_COPY;
 		}
-
-		if (copy_from_user(parg, (void __user *)arg, n))
-			return -EFAULT;
-
-		/* zero out anything we don't copy from userspace */
-		if (n < _IOC_SIZE(cmd))
-			memset((u8 *)parg + n, 0, _IOC_SIZE(cmd) - n);
-		break;
 	}
 
-	return 0;
+	/* zero out anything we don't copy from userspace */
+	if (!err && n < _IOC_SIZE(real_cmd))
+		memset((u8 *)parg + n, 0, _IOC_SIZE(real_cmd) - n);
+	return err;
 }
 
-static int video_put_user(void __user *arg, void *parg, unsigned int cmd)
+static int video_put_user(void __user *arg, void *parg,
+			  unsigned int real_cmd, unsigned int cmd)
 {
 	if (!(_IOC_DIR(cmd) & _IOC_READ))
 		return 0;
 
+	if (cmd == real_cmd) {
+		/*  Copy results into user buffer  */
+		if (copy_to_user(arg, parg, _IOC_SIZE(cmd)))
+			return -EFAULT;
+		return 0;
+	}
+
+	if (in_compat_syscall())
+		return v4l2_compat_put_user(arg, parg, cmd);
+
 	switch (cmd) {
 #ifdef CONFIG_COMPAT_32BIT_TIME
 	case VIDIOC_DQEVENT_TIME32: {
@@ -3236,11 +3250,6 @@ static int video_put_user(void __user *arg, void *parg, unsigned int cmd)
 		break;
 	}
 #endif
-	default:
-		/*  Copy results into user buffer  */
-		if (copy_to_user(arg, parg, _IOC_SIZE(cmd)))
-			return -EFAULT;
-		break;
 	}
 
 	return 0;
@@ -3274,8 +3283,8 @@ video_usercopy(struct file *file, unsigned int orig_cmd, unsigned long arg,
 			parg = mbuf;
 		}
 
-		err = video_get_user((void __user *)arg, parg, orig_cmd,
-				     &always_copy);
+		err = video_get_user((void __user *)arg, parg, cmd,
+				     orig_cmd, &always_copy);
 		if (err)
 			goto out;
 	}
@@ -3297,7 +3306,14 @@ video_usercopy(struct file *file, unsigned int orig_cmd, unsigned long arg,
 		if (NULL == mbuf)
 			goto out_array_args;
 		err = -EFAULT;
-		if (copy_from_user(mbuf, user_ptr, array_size))
+		if (in_compat_syscall())
+			err = v4l2_compat_get_array_args(file, mbuf, user_ptr,
+							 array_size, orig_cmd,
+							 parg);
+		else
+			err = copy_from_user(mbuf, user_ptr, array_size) ?
+								-EFAULT : 0;
+		if (err)
 			goto out_array_args;
 		*kernel_ptr = mbuf;
 	}
@@ -3318,8 +3334,17 @@ video_usercopy(struct file *file, unsigned int orig_cmd, unsigned long arg,
 
 	if (has_array_args) {
 		*kernel_ptr = (void __force *)user_ptr;
-		if (copy_to_user(user_ptr, mbuf, array_size))
+		if (in_compat_syscall()) {
+			int put_err;
+
+			put_err = v4l2_compat_put_array_args(file, user_ptr, mbuf,
+							     array_size, orig_cmd,
+							     parg);
+			if (put_err)
+				err = put_err;
+		} else if (copy_to_user(user_ptr, mbuf, array_size)) {
 			err = -EFAULT;
+		}
 		goto out_array_args;
 	}
 	/*
@@ -3330,7 +3355,7 @@ video_usercopy(struct file *file, unsigned int orig_cmd, unsigned long arg,
 		goto out;
 
 out_array_args:
-	if (video_put_user((void __user *)arg, parg, orig_cmd))
+	if (video_put_user((void __user *)arg, parg, cmd, orig_cmd))
 		err = -EFAULT;
 out:
 	kvfree(mbuf);

include/media/v4l2-ioctl.h

@@ -686,6 +686,16 @@ long int v4l2_compat_ioctl32(struct file *file, unsigned int cmd,
 			     unsigned long arg);
 #endif
 
+unsigned int v4l2_compat_translate_cmd(unsigned int cmd);
+int v4l2_compat_get_user(void __user *arg, void *parg, unsigned int cmd);
+int v4l2_compat_put_user(void __user *arg, void *parg, unsigned int cmd);
+int v4l2_compat_get_array_args(struct file *file, void *mbuf,
+			       void __user *user_ptr, size_t array_size,
+			       unsigned int cmd, void *arg);
+int v4l2_compat_put_array_args(struct file *file, void __user *user_ptr,
+			       void *mbuf, size_t array_size,
+			       unsigned int cmd, void *arg);
+
 /**
  * typedef v4l2_kioctl - Typedef used to pass an ioctl handler.
  *