ext4 crypto: add symlink encryption

Signed-off-by: Uday Savagaonkar <savagaon@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/ext4.h

@@ -2233,6 +2233,7 @@ extern int ext4_group_add_blocks(handle_t *handle, struct super_block *sb,
 extern int ext4_trim_fs(struct super_block *, struct fstrim_range *);
 
 /* inode.c */
+int ext4_inode_is_fast_symlink(struct inode *inode);
 struct buffer_head *ext4_getblk(handle_t *, struct inode *, ext4_lblk_t, int);
 struct buffer_head *ext4_bread(handle_t *, struct inode *, ext4_lblk_t, int);
 int ext4_get_block_write(struct inode *inode, sector_t iblock,

fs/ext4/ext4_crypto.h

@@ -124,4 +124,24 @@ struct ext4_fname_crypto_ctx {
 	unsigned ctfm_key_is_ready : 1;
 };
 
+/**
+ * For encrypted symlinks, the ciphertext length is stored at the beginning
+ * of the string in little-endian format.
+ */
+struct ext4_encrypted_symlink_data {
+	__le16 len;
+	char encrypted_path[1];
+} __attribute__((__packed__));
+
+/**
+ * This function is used to calculate the disk space required to
+ * store a filename of length l in encrypted symlink format.
+ */
+static inline u32 encrypted_symlink_data_len(u32 l)
+{
+	if (l < EXT4_CRYPTO_BLOCK_SIZE)
+		l = EXT4_CRYPTO_BLOCK_SIZE;
+	return (l + sizeof(struct ext4_encrypted_symlink_data) - 1);
+}
+
 #endif	/* _EXT4_CRYPTO_H */

fs/ext4/inode.c

@@ -139,7 +139,7 @@ static int ext4_meta_trans_blocks(struct inode *inode, int lblocks,
 /*
  * Test whether an inode is a fast symlink.
  */
-static int ext4_inode_is_fast_symlink(struct inode *inode)
+int ext4_inode_is_fast_symlink(struct inode *inode)
 {
         int ea_blocks = EXT4_I(inode)->i_file_acl ?
 		EXT4_CLUSTER_SIZE(inode->i_sb) >> 9 : 0;
@@ -4215,7 +4215,8 @@ struct inode *ext4_iget(struct super_block *sb, unsigned long ino)
 		inode->i_op = &ext4_dir_inode_operations;
 		inode->i_fop = &ext4_dir_operations;
 	} else if (S_ISLNK(inode->i_mode)) {
-		if (ext4_inode_is_fast_symlink(inode)) {
+		if (ext4_inode_is_fast_symlink(inode) &&
+		    !ext4_encrypted_inode(inode)) {
 			inode->i_op = &ext4_fast_symlink_inode_operations;
 			nd_terminate_link(ei->i_data, inode->i_size,
 				sizeof(ei->i_data) - 1);

fs/ext4/namei.c

@@ -3193,16 +3193,24 @@ static int ext4_symlink(struct inode *dir,
 {
 	handle_t *handle;
 	struct inode *inode;
-	int l, err, retries = 0;
+	int err, len = strlen(symname);
 	int credits;
+	bool encryption_required;
+	struct ext4_str disk_link;
+	struct ext4_encrypted_symlink_data *sd = NULL;
 
-	l = strlen(symname)+1;
+	disk_link.len = len + 1;
-	if (l > dir->i_sb->s_blocksize)
+	disk_link.name = (char *) symname;
+
+	encryption_required = ext4_encrypted_inode(dir);
+	if (encryption_required)
+		disk_link.len = encrypted_symlink_data_len(len) + 1;
+	if (disk_link.len > dir->i_sb->s_blocksize)
 		return -ENAMETOOLONG;
 
 	dquot_initialize(dir);
 
-	if (l > EXT4_N_BLOCKS * 4) {
+	if ((disk_link.len > EXT4_N_BLOCKS * 4)) {
 		/*
 		 * For non-fast symlinks, we just allocate inode and put it on
 		 * orphan list in the first transaction => we need bitmap,
@@ -3221,16 +3229,49 @@ static int ext4_symlink(struct inode *dir,
 		credits = EXT4_DATA_TRANS_BLOCKS(dir->i_sb) +
 			  EXT4_INDEX_EXTRA_TRANS_BLOCKS + 3;
 	}
-retry:
+
 	inode = ext4_new_inode_start_handle(dir, S_IFLNK|S_IRWXUGO,
 					    &dentry->d_name, 0, NULL,
 					    EXT4_HT_DIR, credits);
 	handle = ext4_journal_current_handle();
-	err = PTR_ERR(inode);
+	if (IS_ERR(inode)) {
-	if (IS_ERR(inode))
+		if (handle)
-		goto out_stop;
+			ext4_journal_stop(handle);
+		return PTR_ERR(inode);
+	}
 
-	if (l > EXT4_N_BLOCKS * 4) {
+	if (encryption_required) {
+		struct ext4_fname_crypto_ctx *ctx = NULL;
+		struct qstr istr;
+		struct ext4_str ostr;
+
+		sd = kzalloc(disk_link.len, GFP_NOFS);
+		if (!sd) {
+			err = -ENOMEM;
+			goto err_drop_inode;
+		}
+		err = ext4_inherit_context(dir, inode);
+		if (err)
+			goto err_drop_inode;
+		ctx = ext4_get_fname_crypto_ctx(inode,
+						inode->i_sb->s_blocksize);
+		if (IS_ERR_OR_NULL(ctx)) {
+			/* We just set the policy, so ctx should not be NULL */
+			err = (ctx == NULL) ? -EIO : PTR_ERR(ctx);
+			goto err_drop_inode;
+		}
+		istr.name = (const unsigned char *) symname;
+		istr.len = len;
+		ostr.name = sd->encrypted_path;
+		err = ext4_fname_usr_to_disk(ctx, &istr, &ostr);
+		ext4_put_fname_crypto_ctx(&ctx);
+		if (err < 0)
+			goto err_drop_inode;
+		sd->len = cpu_to_le16(ostr.len);
+		disk_link.name = (char *) sd;
+	}
+
+	if ((disk_link.len > EXT4_N_BLOCKS * 4)) {
 		inode->i_op = &ext4_symlink_inode_operations;
 		ext4_set_aops(inode);
 		/*
@@ -3246,9 +3287,10 @@ retry:
 		drop_nlink(inode);
 		err = ext4_orphan_add(handle, inode);
 		ext4_journal_stop(handle);
+		handle = NULL;
 		if (err)
 			goto err_drop_inode;
-		err = __page_symlink(inode, symname, l, 1);
+		err = __page_symlink(inode, disk_link.name, disk_link.len, 1);
 		if (err)
 			goto err_drop_inode;
 		/*
@@ -3260,34 +3302,37 @@ retry:
 				EXT4_INDEX_EXTRA_TRANS_BLOCKS + 1);
 		if (IS_ERR(handle)) {
 			err = PTR_ERR(handle);
+			handle = NULL;
 			goto err_drop_inode;
 		}
 		set_nlink(inode, 1);
 		err = ext4_orphan_del(handle, inode);
-		if (err) {
+		if (err)
-			ext4_journal_stop(handle);
-			clear_nlink(inode);
 			goto err_drop_inode;
-		}
 	} else {
 		/* clear the extent format for fast symlink */
 		ext4_clear_inode_flag(inode, EXT4_INODE_EXTENTS);
-		inode->i_op = &ext4_fast_symlink_inode_operations;
+		inode->i_op = encryption_required ?
-		memcpy((char *)&EXT4_I(inode)->i_data, symname, l);
+			&ext4_symlink_inode_operations :
-		inode->i_size = l-1;
+			&ext4_fast_symlink_inode_operations;
+		memcpy((char *)&EXT4_I(inode)->i_data, disk_link.name,
+		       disk_link.len);
+		inode->i_size = disk_link.len - 1;
 	}
 	EXT4_I(inode)->i_disksize = inode->i_size;
 	err = ext4_add_nondir(handle, dentry, inode);
 	if (!err && IS_DIRSYNC(dir))
 		ext4_handle_sync(handle);
 
-out_stop:
 	if (handle)
 		ext4_journal_stop(handle);
-	if (err == -ENOSPC && ext4_should_retry_alloc(dir->i_sb, &retries))
+	kfree(sd);
-		goto retry;
 	return err;
 err_drop_inode:
+	if (handle)
+		ext4_journal_stop(handle);
+	kfree(sd);
+	clear_nlink(inode);
 	unlock_new_inode(inode);
 	iput(inode);
 	return err;

fs/ext4/symlink.c

@@ -22,7 +22,96 @@
 #include "ext4.h"
 #include "xattr.h"
 
+#ifdef CONFIG_EXT4_FS_ENCRYPTION
 static void *ext4_follow_link(struct dentry *dentry, struct nameidata *nd)
+{
+	struct page *cpage = NULL;
+	char *caddr, *paddr = NULL;
+	struct ext4_str cstr, pstr;
+	struct inode *inode = dentry->d_inode;
+	struct ext4_fname_crypto_ctx *ctx = NULL;
+	struct ext4_encrypted_symlink_data *sd;
+	loff_t size = min_t(loff_t, i_size_read(inode), PAGE_SIZE - 1);
+	int res;
+	u32 plen, max_size = inode->i_sb->s_blocksize;
+
+	if (!ext4_encrypted_inode(inode))
+		return page_follow_link_light(dentry, nd);
+
+	ctx = ext4_get_fname_crypto_ctx(inode, inode->i_sb->s_blocksize);
+	if (IS_ERR(ctx))
+		return ctx;
+
+	if (ext4_inode_is_fast_symlink(inode)) {
+		caddr = (char *) EXT4_I(dentry->d_inode)->i_data;
+		max_size = sizeof(EXT4_I(dentry->d_inode)->i_data);
+	} else {
+		cpage = read_mapping_page(inode->i_mapping, 0, NULL);
+		if (IS_ERR(cpage)) {
+			ext4_put_fname_crypto_ctx(&ctx);
+			return cpage;
+		}
+		caddr = kmap(cpage);
+		caddr[size] = 0;
+	}
+
+	/* Symlink is encrypted */
+	sd = (struct ext4_encrypted_symlink_data *)caddr;
+	cstr.name = sd->encrypted_path;
+	cstr.len  = le32_to_cpu(sd->len);
+	if ((cstr.len +
+	     sizeof(struct ext4_encrypted_symlink_data) - 1) >
+	    max_size) {
+		/* Symlink data on the disk is corrupted */
+		res = -EIO;
+		goto errout;
+	}
+	plen = (cstr.len < EXT4_FNAME_CRYPTO_DIGEST_SIZE*2) ?
+		EXT4_FNAME_CRYPTO_DIGEST_SIZE*2 : cstr.len;
+	paddr = kmalloc(plen + 1, GFP_NOFS);
+	if (!paddr) {
+		res = -ENOMEM;
+		goto errout;
+	}
+	pstr.name = paddr;
+	res = _ext4_fname_disk_to_usr(ctx, &cstr, &pstr);
+	if (res < 0)
+		goto errout;
+	/* Null-terminate the name */
+	if (res <= plen)
+		paddr[res] = '\0';
+	nd_set_link(nd, paddr);
+	ext4_put_fname_crypto_ctx(&ctx);
+	if (cpage) {
+		kunmap(cpage);
+		page_cache_release(cpage);
+	}
+	return NULL;
+errout:
+	ext4_put_fname_crypto_ctx(&ctx);
+	if (cpage) {
+		kunmap(cpage);
+		page_cache_release(cpage);
+	}
+	kfree(paddr);
+	return ERR_PTR(res);
+}
+
+static void ext4_put_link(struct dentry *dentry, struct nameidata *nd,
+			  void *cookie)
+{
+	struct page *page = cookie;
+
+	if (!page) {
+		kfree(nd_get_link(nd));
+	} else {
+		kunmap(page);
+		page_cache_release(page);
+	}
+}
+#endif
+
+static void *ext4_follow_fast_link(struct dentry *dentry, struct nameidata *nd)
 {
 	struct ext4_inode_info *ei = EXT4_I(dentry->d_inode);
 	nd_set_link(nd, (char *) ei->i_data);
@@ -31,8 +120,13 @@ static void *ext4_follow_link(struct dentry *dentry, struct nameidata *nd)
 
 const struct inode_operations ext4_symlink_inode_operations = {
 	.readlink	= generic_readlink,
+#ifdef CONFIG_EXT4_FS_ENCRYPTION
+	.follow_link    = ext4_follow_link,
+	.put_link       = ext4_put_link,
+#else
 	.follow_link	= page_follow_link_light,
 	.put_link	= page_put_link,
+#endif
 	.setattr	= ext4_setattr,
 	.setxattr	= generic_setxattr,
 	.getxattr	= generic_getxattr,
@@ -42,7 +136,7 @@ const struct inode_operations ext4_symlink_inode_operations = {
 
 const struct inode_operations ext4_fast_symlink_inode_operations = {
 	.readlink	= generic_readlink,
-	.follow_link	= ext4_follow_link,
+	.follow_link    = ext4_follow_fast_link,
 	.setattr	= ext4_setattr,
 	.setxattr	= generic_setxattr,
 	.getxattr	= generic_getxattr,