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authorJann Horn <jannh@google.com>2022-01-14 16:33:30 +0300
committerJiri Kosina <jkosina@suse.cz>2022-01-19 17:59:05 +0300
commit4ea5763fb79ed89b3bdad455ebf3f33416a81624 (patch)
tree0b0dcbdef3fa8d32b09e9a99c03729cb58eb7013 /drivers
parente24aeff6db738be7ce24999a41e91299b5fe14be (diff)
downloadlinux-4ea5763fb79ed89b3bdad455ebf3f33416a81624.tar.xz
HID: uhid: Fix worker destroying device without any protection
uhid has to run hid_add_device() from workqueue context while allowing parallel use of the userspace API (which is protected with ->devlock). But hid_add_device() can fail. Currently, that is handled by immediately destroying the associated HID device, without using ->devlock - but if there are concurrent requests from userspace, that's wrong and leads to NULL dereferences and/or memory corruption (via use-after-free). Fix it by leaving the HID device as-is in the worker. We can clean it up later, either in the UHID_DESTROY command handler or in the ->release() handler. Cc: stable@vger.kernel.org Fixes: 67f8ecc550b5 ("HID: uhid: fix timeout when probe races with IO") Signed-off-by: Jann Horn <jannh@google.com> Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Diffstat (limited to 'drivers')
-rw-r--r--drivers/hid/uhid.c29
1 files changed, 25 insertions, 4 deletions
diff --git a/drivers/hid/uhid.c b/drivers/hid/uhid.c
index 8fe3efcb8327..fc06d8bb42e0 100644
--- a/drivers/hid/uhid.c
+++ b/drivers/hid/uhid.c
@@ -28,11 +28,22 @@
struct uhid_device {
struct mutex devlock;
+
+ /* This flag tracks whether the HID device is usable for commands from
+ * userspace. The flag is already set before hid_add_device(), which
+ * runs in workqueue context, to allow hid_add_device() to communicate
+ * with userspace.
+ * However, if hid_add_device() fails, the flag is cleared without
+ * holding devlock.
+ * We guarantee that if @running changes from true to false while you're
+ * holding @devlock, it's still fine to access @hid.
+ */
bool running;
__u8 *rd_data;
uint rd_size;
+ /* When this is NULL, userspace may use UHID_CREATE/UHID_CREATE2. */
struct hid_device *hid;
struct uhid_event input_buf;
@@ -63,9 +74,18 @@ static void uhid_device_add_worker(struct work_struct *work)
if (ret) {
hid_err(uhid->hid, "Cannot register HID device: error %d\n", ret);
- hid_destroy_device(uhid->hid);
- uhid->hid = NULL;
+ /* We used to call hid_destroy_device() here, but that's really
+ * messy to get right because we have to coordinate with
+ * concurrent writes from userspace that might be in the middle
+ * of using uhid->hid.
+ * Just leave uhid->hid as-is for now, and clean it up when
+ * userspace tries to close or reinitialize the uhid instance.
+ *
+ * However, we do have to clear the ->running flag and do a
+ * wakeup to make sure userspace knows that the device is gone.
+ */
uhid->running = false;
+ wake_up_interruptible(&uhid->report_wait);
}
}
@@ -474,7 +494,7 @@ static int uhid_dev_create2(struct uhid_device *uhid,
void *rd_data;
int ret;
- if (uhid->running)
+ if (uhid->hid)
return -EALREADY;
rd_size = ev->u.create2.rd_size;
@@ -556,7 +576,7 @@ static int uhid_dev_create(struct uhid_device *uhid,
static int uhid_dev_destroy(struct uhid_device *uhid)
{
- if (!uhid->running)
+ if (!uhid->hid)
return -EINVAL;
uhid->running = false;
@@ -565,6 +585,7 @@ static int uhid_dev_destroy(struct uhid_device *uhid)
cancel_work_sync(&uhid->worker);
hid_destroy_device(uhid->hid);
+ uhid->hid = NULL;
kfree(uhid->rd_data);
return 0;