mei: revamp read and write length checks

1. Return zero on zero length read and writes
2. For a too large write return -EFBIG as defined in man write(2)
EFBIG  An attempt was made to write a file that
        exceeds the implementation-defined maximum
        file size or the process's file size limit,
        or to  write  at  a  position  past  the  maximum
        allowed offset.

Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 14 insertions, 2 deletions

diff --git a/drivers/misc/mei/main.c b/drivers/misc/mei/main.c
index 5ff810b1e8b3..7404584e65e1 100644
--- a/drivers/misc/mei/main.c
+++ b/drivers/misc/mei/main.c
@@ -203,12 +203,18 @@ static ssize_t mei_read(struct file *file, char __user *ubuf,
 
         dev = cl->dev;
 
+
         mutex_lock(&dev->device_lock);
         if (dev->dev_state != MEI_DEV_ENABLED) {
                 rets = -ENODEV;
                 goto out;
         }
 
+        if (length == 0) {
+                rets = 0;
+                goto out;
+        }
+
         if (cl == &dev->iamthif_cl) {
                 rets = mei_amthif_read(dev, file, ubuf, length, offset);
                 goto out;
@@ -350,8 +356,14 @@ static ssize_t mei_write(struct file *file, const char __user *ubuf,
                 rets = -ENODEV;
                 goto out;
         }
-        if (length > dev->me_clients[id].props.max_msg_length || length <= 0) {
-                rets = -EMSGSIZE;
+
+        if (length == 0) {
+                rets = 0;
+                goto out;
+        }
+
+        if (length > dev->me_clients[id].props.max_msg_length) {
+                rets = -EFBIG;
                 goto out;
         }