[PATCH] fat: Fix for invalid cluster sizes

[Sebastian Huber]

A cluster size > 32KiB resulted in an infinite loop in
fat_init_volume_info() due to an integer overflow.

Close #2717.
---
 cpukit/libfs/src/dosfs/fat.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/cpukit/libfs/src/dosfs/fat.c b/cpukit/libfs/src/dosfs/fat.c
index 59f5309..2176ff3 100644
--- a/cpukit/libfs/src/dosfs/fat.c
+++ b/cpukit/libfs/src/dosfs/fat.c
@@ -574,12 +574,14 @@ fat_init_volume_info(fat_fs_info_t *fs_info, const char *device)
     /*
      * "bytes per cluster" value greater than 32K is invalid
      */
-    if ((vol->bpc = vol->bps << vol->spc_log2) > MS_BYTES_PER_CLUSTER_LIMIT)
+    if (vol->bps > (MS_BYTES_PER_CLUSTER_LIMIT >> vol->spc_log2))
     {
         close(vol->fd);
         rtems_set_errno_and_return_minus_one(EINVAL);
     }
 
+    vol->bpc = vol->bps << vol->spc_log2;
+
     for (vol->bpc_log2 = 0, i = vol->bpc; (i & 1) == 0;
          i >>= 1, vol->bpc_log2++);
 
-- 
1.8.4.5