HID: hidraw: fix data race on device refcount

The hidraw_open() function increments the hidraw device reference
counter. The counter has no dedicated synchronization mechanism,
resulting in a potential data race when concurrently opening a device.

The race is a regression introduced by commit 8590222e4b02 ("HID:
hidraw: Replace hidraw device table mutex with a rwsem"). While
minors_rwsem is intended to protect the hidraw_table itself, by instead
acquiring the lock for writing, the reference counter is also protected.
This is symmetrical to hidraw_release().

Link: https://github.com/systemd/systemd/issues/27947
Fixes: 8590222e4b02 ("HID: hidraw: Replace hidraw device table mutex with a rwsem")
Cc: stable@vger.kernel.org
Signed-off-by: Ludvig Michaelsson <ludvig.michaelsson@yubico.com>
Link: https://lore.kernel.org/r/20230621-hidraw-race-v1-1-a58e6ac69bab@yubico.com
Signed-off-by: Benjamin Tissoires <benjamin.tissoires@redhat.com>

diff --git a/drivers/hid/hidraw.c b/drivers/hid/hidraw.c
index 197b1e7bf029e64f4a1874f80ae4b24d2553621c..b617aada50b06dfdb7805a64923ffdce325e9cb5 100644 (file)
--- a/drivers/hid/hidraw.c
+++ b/drivers/hid/hidraw.c
@@ -272,7 +272,12 @@ static int hidraw_open(struct inode *inode, struct file *file)
                goto out;
        }
 
-       down_read(&minors_rwsem);
+       /*
+        * Technically not writing to the hidraw_table but a write lock is
+        * required to protect the device refcount. This is symmetrical to
+        * hidraw_release().
+        */
+       down_write(&minors_rwsem);
        if (!hidraw_table[minor] || !hidraw_table[minor]->exist) {
                err = -ENODEV;
                goto out_unlock;
@@ -301,7 +306,7 @@ static int hidraw_open(struct inode *inode, struct file *file)
        spin_unlock_irqrestore(&hidraw_table[minor]->list_lock, flags);
        file->private_data = list;
 out_unlock:
-       up_read(&minors_rwsem);
+       up_write(&minors_rwsem);
 out:
        if (err < 0)
                kfree(list);