Re: uhid: broken interface: 32/64-bit compatibility

From: Dmitry Torokhov
Date: Fri Feb 15 2013 - 15:05:43 EST

On Fri, Feb 15, 2013 at 03:51:41PM +0200, Kirill A. Shutemov wrote:
> Johan Hedberg wrote:
> > Hi David,
> >
> > On Fri, Feb 15, 2013, David Herrmann wrote:
> > > On Fri, Feb 15, 2013 at 12:29 PM, Kirill A. Shutemov
> > > <kirill.shutemov@xxxxxxxxxxxxxxx> wrote:
> > > > Hi David and all,
> > > >
> > > > There's claim in uhid.h that the interface is "compatible even between
> > > > architectures". But it obviously is not true: struct uhid_create_req
> > > > contains pointer which breaks everything.
> > > >
> > > > The easy way to demonstrate the issue is compile uhid-example.c with -m32
> > > > and try to run it on 64 bit kernel. Creating of the device will fail.
> > >
> > > Indeed, we missed that. We should probably also notify the HIDP
> > > developers as "struct hidp_connadd_req" suffers from the same
> > > problems. (CC'ed)
> > >
> > > > I don't see an easy way to fix this. Few options:
> > > >
> > > > 1. Replace the pointer with u64. It will fix the issue, but it breaks ABI
> > > > which is never a good idea. Not sure how many users interface already
> > > > has.
> > >
> > > The only users I am aware of is an HID debugging tool and experimental
> > > HoG Bluetooth support (bluez). Maybe Marcel or Johan can comment
> > > whether this is already used by bluez-5? If it is, then we shouldn't
> > > break ABI and go with #2+#3. Otherwise, I think changing to u64 should
> > > be ok.
> > > On the other hand, it would break any future build for older stable
> > > kernels so not breaking ABI is probably the best idea. Any comments? I
> > > can add a COMPAT fix and a comment to fix this in the next version of
> > > UHID_CREATE.
> >
> > The HoG code in BlueZ 5 does indeed use this API and it's also not
> > anymore behind any kind of experimental flag (i.e. it is an officially
> > supported feature).
> >
> > Johan
>
> Here's my attempt to fix the issue.
>
> Not sure if tricks with padding in a good idea. We can just use __u64
> instead of pointer, but it will require update of userspace to silence
> cast warning and will cause warning if you will try to use updated
> userspace with old kernel headers.
>
> Any comments?

This does not fix anything really, we simply have to deal with compat
interface.

Compiled but not tested.

Thanks.

--
Dmitry

UHID: make creating devices work on 64/32 systems

From: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>

Unfortunately UHID interface, as it was introduced, is broken with 32 bit
userspace running on 64 bit kernels as it uses a pointer in its userspace
facing API.

Fix it by checking if we are executing compat task and munge the request
appropriately.

Reported-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@xxxxxxxxx>
---
drivers/hid/uhid.c | 95 ++++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 92 insertions(+), 3 deletions(-)

diff --git a/drivers/hid/uhid.c b/drivers/hid/uhid.c
index 714cd8c..fc307e0 100644
--- a/drivers/hid/uhid.c
+++ b/drivers/hid/uhid.c
@@ -11,6 +11,7 @@
*/

#include <linux/atomic.h>
+#include <linux/compat.h>
#include <linux/device.h>
#include <linux/fs.h>
#include <linux/hid.h>
@@ -276,6 +277,94 @@ static struct hid_ll_driver uhid_hid_driver = {
.parse = uhid_hid_parse,
};

+#ifdef CONFIG_COMPAT
+
+/* Apparently we haven't stepped on these rakes enough times yet. */
+struct uhid_create_req_compat {
+ __u8 name[128];
+ __u8 phys[64];
+ __u8 uniq[64];
+
+ compat_uptr_t rd_data;
+ __u16 rd_size;
+
+ __u16 bus;
+ __u32 vendor;
+ __u32 product;
+ __u32 version;
+ __u32 country;
+} __attribute__((__packed__));
+
+static int uhid_event_from_user(const char __user *buffer, size_t len,
+ struct uhid_event *event)
+{
+ if (is_compat_task()) {
+ u32 type;
+
+ if (get_user(type, buffer))
+ return -EFAULT;
+
+ if (type == UHID_CREATE) {
+ /*
+ * This is our messed up request with compat pointer.
+ * It is largish (more than 256 bytes) so we better
+ * allocate it from the heap.
+ */
+ struct uhid_create_req_compat *compat;
+
+ compat = kmalloc(sizeof(*compat), GFP_KERNEL);
+ if (!compat)
+ return -ENOMEM;
+
+ buffer += sizeof(type);
+ len -= sizeof(type);
+ if (copy_from_user(compat, buffer,
+ min(len, sizeof(*compat)))) {
+ kfree(compat);
+ return -EFAULT;
+ }
+
+ /* Shuffle the data over to proper structure */
+ event->type = type;
+
+ memcpy(event->u.create.name, compat->name,
+ sizeof(compat->name));
+ memcpy(event->u.create.phys, compat->phys,
+ sizeof(compat->phys));
+ memcpy(event->u.create.uniq, compat->uniq,
+ sizeof(compat->uniq));
+
+ event->u.create.rd_data = compat_ptr(compat->rd_data);
+ event->u.create.rd_size = compat->rd_size;
+
+ event->u.create.bus = compat->bus;
+ event->u.create.vendor = compat->vendor;
+ event->u.create.product = compat->product;
+ event->u.create.version = compat->version;
+ event->u.create.country = compat->country;
+
+ kfree(compat);
+ return 0;
+ }
+ /* All others can be copied directly */
+ }
+
+ if (copy_from_user(event, buffer, min(len, sizeof(*event))))
+ return -EFAULT;
+
+ return 0;
+}
+#else
+static int uhid_event_from_user(const char __user *buffer, size_t len,
+ struct uhid_event *event)
+{
+ if (copy_from_user(event, buffer, min(len, sizeof(*event))))
+ return -EFAULT;
+
+ return 0;
+}
+#endif
+
static int uhid_dev_create(struct uhid_device *uhid,
const struct uhid_event *ev)
{
@@ -498,10 +587,10 @@ static ssize_t uhid_char_write(struct file *file, const char __user *buffer,

memset(&uhid->input_buf, 0, sizeof(uhid->input_buf));
len = min(count, sizeof(uhid->input_buf));
- if (copy_from_user(&uhid->input_buf, buffer, len)) {
- ret = -EFAULT;
+
+ ret = uhid_event_from_user(buffer, len, &uhid->input_buf);
+ if (ret)
goto unlock;
- }

switch (uhid->input_buf.type) {
case UHID_CREATE:

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