[PATCH v2 1/8] media: v4l2: prepare compat-ioctl rework

Arnd Bergmann
2020-10-30T16:55:46Z

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.

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>
---
drivers/media/v4l2-core/v4l2-compat-ioctl32.c | 53 ++++++
drivers/media/v4l2-core/v4l2-ioctl.c | 159 ++++++++++--------
include/media/v4l2-ioctl.h | 11 ++
3 files changed, 156 insertions(+), 67 deletions(-)

diff --git a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c b/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
index a99e82ec9ab6..7c939d5c5232 100644
--- a/drivers/media/v4l2-core/v4l2-compat-ioctl32.c
+++ b/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.
diff --git a/drivers/media/v4l2-core/v4l2-ioctl.c b/drivers/media/v4l2-core/v4l2-ioctl.c
index eeff398fbdcc..b8be61a09776 100644
--- a/drivers/media/v4l2-core/v4l2-ioctl.c
+++ b/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 */
@@ -3119,73 +3124,82 @@ static int video_get_user(void __user *arg, void *parg, unsigned int cmd,
return 0;
}

- switch (cmd) {
-#ifdef CONFIG_COMPAT_32BIT_TIME
- case VIDIOC_QUERYBUF_TIME32:
- case VIDIOC_QBUF_TIME32:
- case VIDIOC_DQBUF_TIME32:
- case VIDIOC_PREPARE_BUF_TIME32: {
- struct v4l2_buffer_time32 vb32;
- struct v4l2_buffer *vb = parg;
-
- if (copy_from_user(&vb32, arg, sizeof(vb32)))
- return -EFAULT;
-
- *vb = (struct v4l2_buffer) {
- .index = vb32.index,
- .type = vb32.type,
- .bytesused = vb32.bytesused,
- .flags = vb32.flags,
- .field = vb32.field,
- .timestamp.tv_sec = vb32.timestamp.tv_sec,
- .timestamp.tv_usec = vb32.timestamp.tv_usec,
- .timecode = vb32.timecode,
- .sequence = vb32.sequence,
- .memory = vb32.memory,
- .m.userptr = vb32.m.userptr,
- .length = vb32.length,
- .request_fd = vb32.request_fd,
- };
-
- if (cmd == VIDIOC_QUERYBUF_TIME32)
- vb->request_fd = 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;

- break;
+ if (flags & INFO_FL_CLEAR_MASK)
+ n = (flags & INFO_FL_CLEAR_MASK) >> 16;
+ *always_copy = flags & INFO_FL_ALWAYS_COPY;
}
-#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 (cmd == real_cmd) {
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;
+ 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:
+ case VIDIOC_QBUF_TIME32:
+ case VIDIOC_DQBUF_TIME32:
+ case VIDIOC_PREPARE_BUF_TIME32: {
+ struct v4l2_buffer_time32 vb32;
+ struct v4l2_buffer *vb = parg;
+
+ if (copy_from_user(&vb32, arg, sizeof(vb32)))
+ return -EFAULT;
+
+ *vb = (struct v4l2_buffer) {
+ .index = vb32.index,
+ .type = vb32.type,
+ .bytesused = vb32.bytesused,
+ .flags = vb32.flags,
+ .field = vb32.field,
+ .timestamp.tv_sec = vb32.timestamp.tv_sec,
+ .timestamp.tv_usec = vb32.timestamp.tv_usec,
+ .timecode = vb32.timecode,
+ .sequence = vb32.sequence,
+ .memory = vb32.memory,
+ .m.userptr = vb32.m.userptr,
+ .length = vb32.length,
+ .request_fd = vb32.request_fd,
+ };
+ break;
+ }
+#endif
+ }
}

- 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);
diff --git a/include/media/v4l2-ioctl.h b/include/media/v4l2-ioctl.h
index 86878fba332b..0db79f36c496 100644
--- a/include/media/v4l2-ioctl.h
+++ b/include/media/v4l2-ioctl.h
@@ -686,6 +686,17 @@ 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.
*
--
2.27.0