ioutil: fix memory access error on from mog_iou_write

sizeof(buf) returns the size of the pointer if buf is a passed
parameter, even if it the function prototype dictates a fixed
size for buf as we do in mog_iou_write.  While we're at it,
make our mog_iou_write buf parameter const.

This bug was introduced in:
commit a960a351b2248a196c91cdbf6256f98e1bc2ef37
"split iostat util% tracking from mountlist"
and never affected an official release of cmogstored.

This bug was caught while testing on a 32-bit GNU/Linux machine.
My normal 32-bit FreeBSD 9.0 environment did not catch this as
iostat on that platform only reports integer percentages and
does not need more than 4 bytes.

2 files changed, 4 insertions, 4 deletions

diff --git a/cmogstored.h b/cmogstored.h
index d5f6137..73e1353 100644
--- a/cmogstored.h
+++ b/cmogstored.h
@@ -486,7 +486,7 @@ bool mog_valid_put_path(const char *buf, size_t len);
 void mog_iou_cleanup_begin(void);
 void mog_iou_cleanup_finish(void);
 void mog_iou_read(dev_t, char buf[MOG_IOUTIL_LEN]);
-void mog_iou_write(dev_t, char buf[MOG_IOUTIL_LEN]);
+void mog_iou_write(dev_t, const char buf[MOG_IOUTIL_LEN]);
 void mog_iou_active(dev_t);
 
 #include "activeq.h"
diff --git a/ioutil.c b/ioutil.c
index 88050a5..9323a32 100644
--- a/ioutil.c
+++ b/ioutil.c
@@ -121,17 +121,17 @@ void mog_iou_read(dev_t st_dev, char buf[MOG_IOUTIL_LEN])
 
         CHECK(int, 0, pthread_mutex_lock(&iou_lock));
         iou = iou_vivify(st_dev);
-        memcpy(buf, iou->util, sizeof(buf));
+        memcpy(buf, iou->util, MOG_IOUTIL_LEN);
         CHECK(int, 0, pthread_mutex_unlock(&iou_lock));
 }
 
-void mog_iou_write(dev_t st_dev, char buf[MOG_IOUTIL_LEN])
+void mog_iou_write(dev_t st_dev, const char buf[MOG_IOUTIL_LEN])
 {
         struct ioutil *iou;
 
         CHECK(int, 0, pthread_mutex_lock(&iou_lock));
         iou = iou_vivify(st_dev);
-        memcpy(iou->util, buf, sizeof(iou->util));
+        memcpy(iou->util, buf, MOG_IOUTIL_LEN);
         CHECK(int, 0, pthread_mutex_unlock(&iou_lock));
 }