From: Joel Becker <joel.becker@oracle.com>
Date: Mon, 16 Aug 2010 19:10:17 +0000 (-0700)
Subject: libfs: Fix shift bug in generic_check_addressable()
X-Git-Url: http://drtracing.org/?a=commitdiff_plain;h=a33f13efe05192e7a805018a2ce2b2afddd04057;p=deliverable%2Flinux.git

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 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;