[PATCH] ext2: Avoid rec_len overflow with 64KB block size

[Theodore Ts'o <tytso@mit.edu>]

From: Jan Kara <jack@suse.cz>

With 64KB blocksize, a directory entry can have size 64KB which does not fit
into 16 bits we have for entry lenght. So we store 0xffff instead and convert
value when read from / written to disk.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Mingming Cao <cmm@us.ibm.com>
---
 fs/ext2/dir.c           |   43 +++++++++++++++++++++++++++++++------------
 include/linux/ext2_fs.h |    1 +
 2 files changed, 32 insertions(+), 12 deletions(-)

diff --git a/fs/ext2/dir.c b/fs/ext2/dir.c
index 2bf49d7..1329bdb 100644
--- a/fs/ext2/dir.c
+++ b/fs/ext2/dir.c
@@ -26,6 +26,24 @@
 
 typedef struct ext2_dir_entry_2 ext2_dirent;
 
+static inline unsigned ext2_rec_len_from_disk(__le16 dlen)
+{
+	unsigned len = le16_to_cpu(dlen);
+
+	if (len == EXT2_MAX_REC_LEN)
+		return 1 << 16;
+	return len;
+}
+
+static inline __le16 ext2_rec_len_to_disk(unsigned len)
+{
+	if (len == (1 << 16))
+		return cpu_to_le16(EXT2_MAX_REC_LEN);
+	else if (len > (1 << 16))
+		BUG();
+	return cpu_to_le16(len);
+}
+
 /*
  * ext2 uses block-sized chunks. Arguably, sector-sized ones would be
  * more robust, but we have what we have
@@ -95,7 +113,7 @@ static void ext2_check_page(struct page *page)
 	}
 	for (offs = 0; offs <= limit - EXT2_DIR_REC_LEN(1); offs += rec_len) {
 		p = (ext2_dirent *)(kaddr + offs);
-		rec_len = le16_to_cpu(p->rec_len);
+		rec_len = ext2_rec_len_from_disk(p->rec_len);
 
 		if (rec_len < EXT2_DIR_REC_LEN(1))
 			goto Eshort;
@@ -193,7 +211,8 @@ static inline int ext2_match (int len, const char * const name,
  */
 static inline ext2_dirent *ext2_next_entry(ext2_dirent *p)
 {
-	return (ext2_dirent *)((char*)p + le16_to_cpu(p->rec_len));
+	return (ext2_dirent *)((char*)p +
+			ext2_rec_len_from_disk(p->rec_len));
 }
 
 static inline unsigned 
@@ -305,7 +324,7 @@ ext2_readdir (struct file * filp, void * dirent, filldir_t filldir)
 					return 0;
 				}
 			}
-			filp->f_pos += le16_to_cpu(de->rec_len);
+			filp->f_pos += ext2_rec_len_from_disk(de->rec_len);
 		}
 		ext2_put_page(page);
 	}
@@ -413,7 +432,7 @@ void ext2_set_link(struct inode *dir, struct ext2_dir_entry_2 *de,
 			struct page *page, struct inode *inode)
 {
 	unsigned from = (char *) de - (char *) page_address(page);
-	unsigned to = from + le16_to_cpu(de->rec_len);
+	unsigned to = from + ext2_rec_len_from_disk(de->rec_len);
 	int err;
 
 	lock_page(page);
@@ -469,7 +488,7 @@ int ext2_add_link (struct dentry *dentry, struct inode *inode)
 				/* We hit i_size */
 				name_len = 0;
 				rec_len = chunk_size;
-				de->rec_len = cpu_to_le16(chunk_size);
+				de->rec_len = ext2_rec_len_to_disk(chunk_size);
 				de->inode = 0;
 				goto got_it;
 			}
@@ -483,7 +502,7 @@ int ext2_add_link (struct dentry *dentry, struct inode *inode)
 			if (ext2_match (namelen, name, de))
 				goto out_unlock;
 			name_len = EXT2_DIR_REC_LEN(de->name_len);
-			rec_len = le16_to_cpu(de->rec_len);
+			rec_len = ext2_rec_len_from_disk(de->rec_len);
 			if (!de->inode && rec_len >= reclen)
 				goto got_it;
 			if (rec_len >= name_len + reclen)
@@ -504,8 +523,8 @@ got_it:
 		goto out_unlock;
 	if (de->inode) {
 		ext2_dirent *de1 = (ext2_dirent *) ((char *) de + name_len);
-		de1->rec_len = cpu_to_le16(rec_len - name_len);
-		de->rec_len = cpu_to_le16(name_len);
+		de1->rec_len = ext2_rec_len_to_disk(rec_len - name_len);
+		de->rec_len = ext2_rec_len_to_disk(name_len);
 		de = de1;
 	}
 	de->name_len = namelen;
@@ -536,7 +555,7 @@ int ext2_delete_entry (struct ext2_dir_entry_2 * dir, struct page * page )
 	struct inode *inode = mapping->host;
 	char *kaddr = page_address(page);
 	unsigned from = ((char*)dir - kaddr) & ~(ext2_chunk_size(inode)-1);
-	unsigned to = ((char*)dir - kaddr) + le16_to_cpu(dir->rec_len);
+	unsigned to = ((char*)dir - kaddr) + ext2_rec_len_from_disk(dir->rec_len);
 	ext2_dirent * pde = NULL;
 	ext2_dirent * de = (ext2_dirent *) (kaddr + from);
 	int err;
@@ -557,7 +576,7 @@ int ext2_delete_entry (struct ext2_dir_entry_2 * dir, struct page * page )
 	err = mapping->a_ops->prepare_write(NULL, page, from, to);
 	BUG_ON(err);
 	if (pde)
-		pde->rec_len = cpu_to_le16(to-from);
+		pde->rec_len = ext2_rec_len_to_disk(to-from);
 	dir->inode = 0;
 	err = ext2_commit_chunk(page, from, to);
 	inode->i_ctime = inode->i_mtime = CURRENT_TIME_SEC;
@@ -591,14 +610,14 @@ int ext2_make_empty(struct inode *inode, struct inode *parent)
 	memset(kaddr, 0, chunk_size);
 	de = (struct ext2_dir_entry_2 *)kaddr;
 	de->name_len = 1;
-	de->rec_len = cpu_to_le16(EXT2_DIR_REC_LEN(1));
+	de->rec_len = ext2_rec_len_to_disk(EXT2_DIR_REC_LEN(1));
 	memcpy (de->name, ".\0\0", 4);
 	de->inode = cpu_to_le32(inode->i_ino);
 	ext2_set_de_type (de, inode);
 
 	de = (struct ext2_dir_entry_2 *)(kaddr + EXT2_DIR_REC_LEN(1));
 	de->name_len = 2;
-	de->rec_len = cpu_to_le16(chunk_size - EXT2_DIR_REC_LEN(1));
+	de->rec_len = ext2_rec_len_to_disk(chunk_size - EXT2_DIR_REC_LEN(1));
 	de->inode = cpu_to_le32(parent->i_ino);
 	memcpy (de->name, "..\0", 4);
 	ext2_set_de_type (de, inode);
diff --git a/include/linux/ext2_fs.h b/include/linux/ext2_fs.h
index 910a705..41063d5 100644
--- a/include/linux/ext2_fs.h
+++ b/include/linux/ext2_fs.h
@@ -557,5 +557,6 @@ enum {
 #define EXT2_DIR_ROUND 			(EXT2_DIR_PAD - 1)
 #define EXT2_DIR_REC_LEN(name_len)	(((name_len) + 8 + EXT2_DIR_ROUND) & \
 					 ~EXT2_DIR_ROUND)
+#define EXT2_MAX_REC_LEN		((1<<16)-1)
 
 #endif	/* _LINUX_EXT2_FS_H */
-- 
1.5.3.2.81.g17ed