1 files changed, 20 insertions, 1 deletions

diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c
index ef8c2ed792c3..a92d81567559 100644
--- a/drivers/input/evdev.c
+++ b/drivers/input/evdev.c
@@ -647,8 +647,10 @@ static int str_to_user(const char *str, unsigned int maxlen, void __user *p)
         return copy_to_user(p, str, len) ? -EFAULT : len;
 }
 
+#define OLD_KEY_MAX     0x1ff
 static int handle_eviocgbit(struct input_dev *dev, unsigned int cmd, void __user *p, int compat_mode)
 {
+        static unsigned long keymax_warn_time;
         unsigned long *bits;
         int len;
 
@@ -665,9 +667,26 @@ static int handle_eviocgbit(struct input_dev *dev, unsigned int cmd, void __user
         case EV_SW:  bits = dev->swbit;  len = SW_MAX;  break;
         default: return -EINVAL;
         }
+
+        /*
+         * Work around bugs in userspace programs that like to do
+         * EVIOCGBIT(EV_KEY, KEY_MAX) and not realize that 'len'
+         * should be in bytes, not in bits.
+         */
+        if ((_IOC_NR(cmd) & EV_MAX) == EV_KEY && _IOC_SIZE(cmd) == OLD_KEY_MAX) {
+                len = OLD_KEY_MAX;
+                if (printk_timed_ratelimit(&keymax_warn_time, 10 * 1000))
+                        printk(KERN_WARNING
+                                "evdev.c(EVIOCGBIT): Suspicious buffer size %d, "
+                                "limiting output to %d bytes. See "
+                                "http://userweb.kernel.org/~dtor/eviocgbit-bug.html\n",
+                                OLD_KEY_MAX,
+                                BITS_TO_LONGS(OLD_KEY_MAX) * sizeof(long));
+        }
+
         return bits_to_user(bits, len, _IOC_SIZE(cmd), p, compat_mode);
 }
-
+#undef OLD_KEY_MAX
 
 static long evdev_do_ioctl(struct file *file, unsigned int cmd,
                            void __user *p, int compat_mode)