diff mbox

HID: uhid: Fixes a bug with userspace bluetooth stacks, which causes hangs during certain operations

Message ID 1461272067-17624-1-git-send-email-roderick@gaikai.com (mailing list archive)
State New, archived
Headers show

Commit Message

Roderick Colenbrander April 21, 2016, 8:54 p.m. UTC 
From: Roderick Colenbrander <roderick.colenbrander@sony.com>

Many devices use userspace bluetooth stacks like BlueZ or Bluedroid in combination
with uhid. If any of these stacks is used with a HID device for which the driver
performs a HID request as part .probe (or technically another HID operation),
this results in a deadlock situation. The deadlock results in a 5 second timeout
for I/O operations in HID drivers, so isn't fatal, but none of the I/O operations
have a chance of succeeding.

The root cause for the problem is that uhid only allows for one request to be
processed at a time per uhid instance and locks out other operations. This means
that if a user space is creating a new HID device through 'UHID_CREATE', which
ultimately triggers '.probe' through the HID layer. Then any HID request e.g. a
read for calibration data would trigger a HID operation on uhid again, but it
won't go out to userspace, because it is still stuck in UHID_CREATE.
In addition bluetooth stacks are typically single threaded, so they wouldn't be
able to handle any requests while waiting on uhid.

Lucikly the UHID spec is somewhat flexible and allows for fixing the issue,
without breaking user space. The idea which the patch implements as discussed
with David Herrmann is to decouple adding of a hid device (which triggers .probe)
from UHID_CREATE. The work will kick off roughly once UHID_CREATE completed (or
else will wait a tiny bit of time in .probe for a lock). A HID driver has to call
HID to call 'hid_hw_start()' as part of .probe once it is ready for I/O, which
triggers UHID_START to user space. Any HID operations should function now within
.probe and won't deadlock because userspace is stuck on UHID_CREATE.

We verified this patch on Bluedroid with Android 6.0 and on desktop Linux with
BlueZ stacks. Prior to the patch they had the deadlock issue.

Signed-off-by: Roderick Colenbrander <roderick.colenbrander@sony.com>
Cc: stable@vger.kernel.org
---
 drivers/hid/uhid.c | 35 +++++++++++++++++++++++++----------
 1 file changed, 25 insertions(+), 10 deletions(-)

Comments

kernel test robot April 21, 2016, 9:15 p.m. UTC | #1 
Hi,

[auto build test ERROR on hid/for-next]
[also build test ERROR on v4.6-rc4 next-20160421]
[if your patch is applied to the wrong git tree, please drop us a note to help improving the system]

url:    https://github.com/0day-ci/linux/commits/roderick-gaikai-com/HID-uhid-Fixes-a-bug-with-userspace-bluetooth-stacks-which-causes-hangs-during-certain-operations/20160422-050505
base:   https://git.kernel.org/pub/scm/linux/kernel/git/jikos/hid.git for-next
config: x86_64-randconfig-x010-201616 (attached as .config)
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

All errors (new ones prefixed by >>):

   drivers/hid/uhid.c: In function 'uhid_event_from_user':
>> drivers/hid/uhid.c:403:6: error: implicit declaration of function 'is_compat_task' [-Werror=implicit-function-declaration]
     if (is_compat_task()) {
         ^
   cc1: some warnings being treated as errors

vim +/is_compat_task +403 drivers/hid/uhid.c

   397		__u32 country;
   398	} __attribute__((__packed__));
   399	
   400	static int uhid_event_from_user(const char __user *buffer, size_t len,
   401					struct uhid_event *event)
   402	{
 > 403		if (is_compat_task()) {
   404			u32 type;
   405	
   406			if (get_user(type, buffer))

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation
kernel test robot April 21, 2016, 9:15 p.m. UTC | #2 
Hi,

[auto build test WARNING on hid/for-next]
[also build test WARNING on v4.6-rc4 next-20160421]
[if your patch is applied to the wrong git tree, please drop us a note to help improving the system]

url:    https://github.com/0day-ci/linux/commits/roderick-gaikai-com/HID-uhid-Fixes-a-bug-with-userspace-bluetooth-stacks-which-causes-hangs-during-certain-operations/20160422-050505
base:   https://git.kernel.org/pub/scm/linux/kernel/git/jikos/hid.git for-next
config: x86_64-randconfig-x003-201616 (attached as .config)
reproduce:
        # save the attached .config to linux build tree
        make ARCH=x86_64 

All warnings (new ones prefixed by >>):

   In file included from arch/x86/include/asm/atomic.h:4:0,
                    from include/linux/atomic.h:4,
                    from drivers/hid/uhid.c:13:
   drivers/hid/uhid.c: In function 'uhid_event_from_user':
   drivers/hid/uhid.c:403:6: error: implicit declaration of function 'is_compat_task' [-Werror=implicit-function-declaration]
     if (is_compat_task()) {
         ^
   include/linux/compiler.h:151:30: note: in definition of macro '__trace_if'
     if (__builtin_constant_p(!!(cond)) ? !!(cond) :   \
                                 ^
>> drivers/hid/uhid.c:403:2: note: in expansion of macro 'if'
     if (is_compat_task()) {
     ^
   cc1: some warnings being treated as errors

vim +/if +403 drivers/hid/uhid.c

   387		__u8 phys[64];
   388		__u8 uniq[64];
   389	
   390		compat_uptr_t rd_data;
   391		__u16 rd_size;
   392	
   393		__u16 bus;
   394		__u32 vendor;
   395		__u32 product;
   396		__u32 version;
   397		__u32 country;
   398	} __attribute__((__packed__));
   399	
   400	static int uhid_event_from_user(const char __user *buffer, size_t len,
   401					struct uhid_event *event)
   402	{
 > 403		if (is_compat_task()) {
   404			u32 type;
   405	
   406			if (get_user(type, buffer))
   407				return -EFAULT;
   408	
   409			if (type == UHID_CREATE) {
   410				/*
   411				 * This is our messed up request with compat pointer.

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation
Roderick Colenbrander April 21, 2016, 9:27 p.m. UTC | #3 
Please ignore this revision of the patch, there was a small merge
conflict on my end.

On Thu, Apr 21, 2016 at 2:15 PM, kbuild test robot <lkp@intel.com> wrote:
> Hi,
>
> [auto build test WARNING on hid/for-next]
> [also build test WARNING on v4.6-rc4 next-20160421]
> [if your patch is applied to the wrong git tree, please drop us a note to help improving the system]
>
> url:    https://github.com/0day-ci/linux/commits/roderick-gaikai-com/HID-uhid-Fixes-a-bug-with-userspace-bluetooth-stacks-which-causes-hangs-during-certain-operations/20160422-050505
> base:   https://git.kernel.org/pub/scm/linux/kernel/git/jikos/hid.git for-next
> config: x86_64-randconfig-x003-201616 (attached as .config)
> reproduce:
>         # save the attached .config to linux build tree
>         make ARCH=x86_64
>
> All warnings (new ones prefixed by >>):
>
>    In file included from arch/x86/include/asm/atomic.h:4:0,
>                     from include/linux/atomic.h:4,
>                     from drivers/hid/uhid.c:13:
>    drivers/hid/uhid.c: In function 'uhid_event_from_user':
>    drivers/hid/uhid.c:403:6: error: implicit declaration of function 'is_compat_task' [-Werror=implicit-function-declaration]
>      if (is_compat_task()) {
>          ^
>    include/linux/compiler.h:151:30: note: in definition of macro '__trace_if'
>      if (__builtin_constant_p(!!(cond)) ? !!(cond) :   \
>                                  ^
>>> drivers/hid/uhid.c:403:2: note: in expansion of macro 'if'
>      if (is_compat_task()) {
>      ^
>    cc1: some warnings being treated as errors
>
> vim +/if +403 drivers/hid/uhid.c
>
>    387          __u8 phys[64];
>    388          __u8 uniq[64];
>    389
>    390          compat_uptr_t rd_data;
>    391          __u16 rd_size;
>    392
>    393          __u16 bus;
>    394          __u32 vendor;
>    395          __u32 product;
>    396          __u32 version;
>    397          __u32 country;
>    398  } __attribute__((__packed__));
>    399
>    400  static int uhid_event_from_user(const char __user *buffer, size_t len,
>    401                                  struct uhid_event *event)
>    402  {
>  > 403          if (is_compat_task()) {
>    404                  u32 type;
>    405
>    406                  if (get_user(type, buffer))
>    407                          return -EFAULT;
>    408
>    409                  if (type == UHID_CREATE) {
>    410                          /*
>    411                           * This is our messed up request with compat pointer.
>
> ---
> 0-DAY kernel test infrastructure                Open Source Technology Center
> https://lists.01.org/pipermail/kbuild-all                   Intel Corporation
diff mbox

Patch

diff --git a/drivers/hid/uhid.c b/drivers/hid/uhid.c
index 16b6f11..1a2032c 100644
--- a/drivers/hid/uhid.c
+++ b/drivers/hid/uhid.c
@@ -51,10 +51,26 @@  struct uhid_device {
 	u32 report_id;
 	u32 report_type;
 	struct uhid_event report_buf;
+	struct work_struct worker;
 };
 
 static struct miscdevice uhid_misc;
 
+static void uhid_device_add_worker(struct work_struct *work)
+{
+	struct uhid_device *uhid = container_of(work, struct uhid_device, worker);
+	int ret;
+
+	ret = hid_add_device(uhid->hid);
+	if (ret) {
+		hid_err(uhid->hid, "Cannot register HID device: error %d\n", ret);
+
+		hid_destroy_device(uhid->hid);
+		uhid->hid = NULL;
+		uhid->running = false;
+	}
+}
+
 static void uhid_queue(struct uhid_device *uhid, struct uhid_event *ev)
 {
 	__u8 newhead;
@@ -384,7 +400,7 @@  struct uhid_create_req_compat {
 static int uhid_event_from_user(const char __user *buffer, size_t len,
 				struct uhid_event *event)
 {
-	if (in_compat_syscall()) {
+	if (is_compat_task()) {
 		u32 type;
 
 		if (get_user(type, buffer))
@@ -498,18 +514,14 @@  static int uhid_dev_create2(struct uhid_device *uhid,
 	uhid->hid = hid;
 	uhid->running = true;
 
-	ret = hid_add_device(hid);
-	if (ret) {
-		hid_err(hid, "Cannot register HID device\n");
-		goto err_hid;
-	}
+	/* Adding of a HID device is done through a worker, to allow HID drivers
+	 * which use feature requests during .probe to work, without they would
+	 * be blocked on devlock, which is held by uhid_char_write.
+	 */
+	schedule_work(&uhid->worker);
 
 	return 0;
 
-err_hid:
-	hid_destroy_device(hid);
-	uhid->hid = NULL;
-	uhid->running = false;
 err_free:
 	kfree(uhid->rd_data);
 	uhid->rd_data = NULL;
@@ -550,6 +562,8 @@  static int uhid_dev_destroy(struct uhid_device *uhid)
 	uhid->running = false;
 	wake_up_interruptible(&uhid->report_wait);
 
+	cancel_work_sync(&uhid->worker);
+
 	hid_destroy_device(uhid->hid);
 	kfree(uhid->rd_data);
 
@@ -612,6 +626,7 @@  static int uhid_char_open(struct inode *inode, struct file *file)
 	init_waitqueue_head(&uhid->waitq);
 	init_waitqueue_head(&uhid->report_wait);
 	uhid->running = false;
+	INIT_WORK(&uhid->worker, uhid_device_add_worker);
 
 	file->private_data = uhid;
 	nonseekable_open(inode, file);