Squashfs: fix variable overflow triggered by sysbot

Sysbot reports a slab out of bounds write in squashfs_readahead().

This is ultimately caused by a file reporting an (infeasibly) large file
size (1407374883553280 bytes) with the minimum block size of 4K.

This causes variable overflow.

Link: https://lkml.kernel.org/r/20231113160901.6444-1-phillip@squashfs.org.ukSigned-off-by: Phillip Lougher <phillip@squashfs.org.uk>
Reported-by: syzbot+604424eb051c2f696163@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/000000000000b1fda20609ede0d1@google.com/Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

fs/squashfs/file.c

@@ -544,7 +544,8 @@ static void squashfs_readahead(struct readahead_control *ractl)
 	struct squashfs_page_actor *actor;
 	unsigned int nr_pages = 0;
 	struct page **pages;
-	int i, file_end = i_size_read(inode) >> msblk->block_log;
+	int i;
+	loff_t file_end = i_size_read(inode) >> msblk->block_log;
 	unsigned int max_pages = 1UL << shift;
 
 	readahead_expand(ractl, start, (len | mask) + 1);

fs/squashfs/file_direct.c

@@ -26,10 +26,10 @@ int squashfs_readpage_block(struct page *target_page, u64 block, int bsize,
 	struct inode *inode = target_page->mapping->host;
 	struct squashfs_sb_info *msblk = inode->i_sb->s_fs_info;
 
-	int file_end = (i_size_read(inode) - 1) >> PAGE_SHIFT;
+	loff_t file_end = (i_size_read(inode) - 1) >> PAGE_SHIFT;
 	int mask = (1 << (msblk->block_log - PAGE_SHIFT)) - 1;
-	int start_index = target_page->index & ~mask;
-	int end_index = start_index | mask;
+	loff_t start_index = target_page->index & ~mask;
+	loff_t end_index = start_index | mask;
 	int i, n, pages, bytes, res = -ENOMEM;
 	struct page **page;
 	struct squashfs_page_actor *actor;