[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/romfs/inode.c

@@ -418,7 +418,7 @@ static int
 romfs_readpage(struct file *file, struct page * page)
 {
 	struct inode *inode = page->mapping->host;
-	unsigned long offset, avail, readlen;
+	loff_t offset, avail, readlen;
 	void *buf;
 	int result = -EIO;
 
@@ -429,8 +429,8 @@ romfs_readpage(struct file *file, struct page * page)
 		goto err_out;
 
 	/* 32 bit warning -- but not for us :) */
-	offset = page->index << PAGE_CACHE_SHIFT;
-	if (offset < inode->i_size) {
+	offset = page_offset(page);
+	if (offset < i_size_read(inode)) {
 		avail = inode->i_size-offset;
 		readlen = min_t(unsigned long, avail, PAGE_SIZE);
 		if (romfs_copyfrom(inode, buf, ROMFS_I(inode)->i_dataoffset+offset, readlen) == readlen) {