f2fs: Restrict max filesize for 16K f2fs

Blocks are tracked by u32, so the max permitted filesize is
(U32_MAX + 1) * BLOCK_SIZE. Additionally, in order to support crypto
data unit sizes of 4K with a 16K block with IV_INO_LBLK_{32,64}, we must
further restrict max filesize to (U32_MAX + 1) * 4096. This does not
affect 4K blocksize f2fs as the natural limit for files are well below
that.

Fixes: d7e9a903 ("f2fs: Support Block Size == Page Size")
Signed-off-by: Daniel Rosenberg <drosen@google.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/super.c

@@ -3359,6 +3359,14 @@ loff_t max_file_blocks(struct inode *inode)
 	leaf_count *= NIDS_PER_BLOCK;
 	result += leaf_count;
 
+	/*
+	 * For compatibility with FSCRYPT_POLICY_FLAG_IV_INO_LBLK_{64,32} with
+	 * a 4K crypto data unit, we must restrict the max filesize to what can
+	 * fit within U32_MAX + 1 data units.
+	 */
+
+	result = min(result, (((loff_t)U32_MAX + 1) * 4096) >> F2FS_BLKSIZE_BITS);
+
 	return result;
 }