libfs: Fix shift bug in generic_check_addressable()

generic_check_addressable() erroneously shifts pages down by a block
factor when it should be shifting up.  To prevent overflow, we shift
blocks down to pages.

Signed-off-by: Joel Becker <joel.becker@oracle.com>

1 files changed, 4 insertions, 4 deletions

diff --git a/fs/libfs.c b/fs/libfs.c
index 8debe7b33769..62baa0387d6e 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -925,6 +925,8 @@ EXPORT_SYMBOL(generic_file_fsync);
 int generic_check_addressable(unsigned blocksize_bits, u64 num_blocks)
 {
         u64 last_fs_block = num_blocks - 1;
+        u64 last_fs_page =
+                last_fs_block >> (PAGE_CACHE_SHIFT - blocksize_bits);
 
         if (unlikely(num_blocks == 0))
                 return 0;
@@ -932,10 +934,8 @@ int generic_check_addressable(unsigned blocksize_bits, u64 num_blocks)
         if ((blocksize_bits < 9) || (blocksize_bits > PAGE_CACHE_SHIFT))
                 return -EINVAL;
 
-        if ((last_fs_block >
-             (sector_t)(~0ULL) >> (blocksize_bits - 9)) ||
-            (last_fs_block >
-             (pgoff_t)(~0ULL) >> (PAGE_CACHE_SHIFT - blocksize_bits))) {
+        if ((last_fs_block > (sector_t)(~0ULL) >> (blocksize_bits - 9)) ||
+            (last_fs_page > (pgoff_t)(~0ULL))) {
                 return -EFBIG;
         }
         return 0;