[PATCH] fix possible PAGE_CACHE_SHIFT overflows

We've had two instances recently of overflows when doing

	64_bit_value = (32_bit_value << PAGE_CACHE_SHIFT)

I did a tree-wide grep of `<<.*PAGE_CACHE_SHIFT' and this is the result.

- afs_rxfs_fetch_descriptor.offset is of type off_t, which seems broken.

- jfs and jffs are limited to 4GB anyway.

- reiserfs map_block_for_writepage() takes an unsigned long for the block -
  it should take sector_t.  (It'll fail for huge filesystems with
  blocksize<PAGE_CACHE_SIZE)

- cramfs_read() needs to use sector_t (I think cramsfs is busted on large
  filesystems anyway)

- affs is limited in file size anyway.

- I generally didn't fix 32-bit overflows in directory operations.

- arm's __flush_dcache_page() is peculiar.  What if the page lies beyond 4G?

- gss_wrap_req_priv() needs checking (snd_buf->page_base)

Cc: Oleg Drokin <[email protected]>
Cc: David Howells <[email protected]>
Cc: David Woodhouse <[email protected]>
Cc: <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Anton Altaparmakov <[email protected]>
Cc: Jeff Dike <[email protected]>
Cc: Paolo 'Blaisorblade' Giarrusso <[email protected]>
Cc: Roman Zippel <[email protected]>
Cc: <[email protected]>
Cc: Miklos Szeredi <[email protected]>
Cc: Russell King <[email protected]>
Cc: Trond Myklebust <[email protected]>
Cc: Neil Brown <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

fs/afs/dir.c

@@ -137,7 +137,7 @@ static inline void afs_dir_check_page(struct inode *dir, struct page *page)
 #endif
 
 	/* determine how many magic numbers there should be in this page */
-	latter = dir->i_size - (page->index << PAGE_CACHE_SHIFT);
+	latter = dir->i_size - page_offset(page);
 	if (latter >= PAGE_SIZE)
 		qty = PAGE_SIZE;
 	else