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>

diff --git a/fs/libfs.c b/fs/libfs.c
index 8debe7b..62baa03 100644 (file)
--- 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;