[PATCH] eCryptfs: Encrypted passthrough

Provide an option to provide a view of the encrypted files such that the
metadata is always in the header of the files, regardless of whether the
metadata is actually in the header or in the extended attribute.  This mode of
operation is useful for applications like incremental backup utilities that do
not preserve the extended attributes when directly accessing the lower files.

With this option enabled, the files under the eCryptfs mount point will be
read-only.
Signed-off-by: Michael Halcrow <mhalcrow@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/ecryptfs/crypto.c

@@ -1256,8 +1256,9 @@ out:
 }
 
 
-static void
-write_header_metadata(char *virt, struct ecryptfs_crypt_stat *crypt_stat,
+void
+ecryptfs_write_header_metadata(char *virt,
+			       struct ecryptfs_crypt_stat *crypt_stat,
 			       size_t *written)
 {
 	u32 header_extent_size;
@@ -1320,7 +1321,8 @@ static int ecryptfs_write_headers_virt(char *page_virt, size_t *size,
 	offset += written;
 	write_ecryptfs_flags((page_virt + offset), crypt_stat, &written);
 	offset += written;
-	write_header_metadata((page_virt + offset), crypt_stat, &written);
+	ecryptfs_write_header_metadata((page_virt + offset), crypt_stat,
+				       &written);
 	offset += written;
 	rc = ecryptfs_generate_key_packet_set((page_virt + offset), crypt_stat,
 					      ecryptfs_dentry, &written,
@@ -1606,7 +1608,12 @@ int ecryptfs_read_metadata(struct dentry *ecryptfs_dentry,
 	ssize_t bytes_read;
 	struct ecryptfs_crypt_stat *crypt_stat =
 	    &ecryptfs_inode_to_private(ecryptfs_dentry->d_inode)->crypt_stat;
+	struct ecryptfs_mount_crypt_stat *mount_crypt_stat =
+		&ecryptfs_superblock_to_private(
+			ecryptfs_dentry->d_sb)->mount_crypt_stat;
 
+	ecryptfs_copy_mount_wide_flags_to_inode_flags(crypt_stat,
+						      mount_crypt_stat);
 	/* Read the first page from the underlying file */
 	page_virt = kmem_cache_alloc(ecryptfs_header_cache_1, GFP_USER);
 	if (!page_virt) {

fs/ecryptfs/ecryptfs_kernel.h

@@ -559,7 +559,7 @@ ssize_t ecryptfs_getxattr(struct dentry *dentry, const char *name, void *value,
 int
 ecryptfs_setxattr(struct dentry *dentry, const char *name, const void *value,
 		  size_t size, int flags);
-
+int ecryptfs_read_xattr_region(char *page_virt, struct dentry *ecryptfs_dentry);
 int ecryptfs_process_helo(unsigned int transport, uid_t uid, pid_t pid);
 int ecryptfs_process_quit(uid_t uid, pid_t pid);
 int ecryptfs_process_response(struct ecryptfs_message *msg, uid_t uid,
@@ -582,6 +582,9 @@ int ecryptfs_send_connector(char *data, int data_len,
 			    u16 msg_flags, pid_t daemon_pid);
 int ecryptfs_init_connector(void);
 void ecryptfs_release_connector(void);
-
+void
+ecryptfs_write_header_metadata(char *virt,
+			       struct ecryptfs_crypt_stat *crypt_stat,
+			       size_t *written);
 
 #endif /* #ifndef ECRYPTFS_KERNEL_H */

fs/ecryptfs/file.c

@@ -250,6 +250,17 @@ static int ecryptfs_open(struct inode *inode, struct file *file)
 	struct ecryptfs_file_info *file_info;
 	int lower_flags;
 
+	mount_crypt_stat = &ecryptfs_superblock_to_private(
+		ecryptfs_dentry->d_sb)->mount_crypt_stat;
+	if ((mount_crypt_stat->flags & ECRYPTFS_ENCRYPTED_VIEW_ENABLED)
+	    && ((file->f_flags & O_WRONLY) || (file->f_flags & O_RDWR)
+		|| (file->f_flags & O_CREAT) || (file->f_flags & O_TRUNC)
+		|| (file->f_flags & O_APPEND))) {
+		printk(KERN_WARNING "Mount has encrypted view enabled; "
+		       "files may only be read\n");
+		rc = -EPERM;
+		goto out;
+	}
 	/* Released in ecryptfs_release or end of function if failure */
 	file_info = kmem_cache_zalloc(ecryptfs_file_info_cache, GFP_KERNEL);
 	ecryptfs_set_file_private(file, file_info);
@@ -261,8 +272,6 @@ static int ecryptfs_open(struct inode *inode, struct file *file)
 	}
 	lower_dentry = ecryptfs_dentry_to_lower(ecryptfs_dentry);
 	crypt_stat = &ecryptfs_inode_to_private(inode)->crypt_stat;
-	mount_crypt_stat = &ecryptfs_superblock_to_private(
-		ecryptfs_dentry->d_sb)->mount_crypt_stat;
 	mutex_lock(&crypt_stat->cs_mutex);
 	if (!ECRYPTFS_CHECK_FLAG(crypt_stat->flags, ECRYPTFS_POLICY_APPLIED)) {
 		ecryptfs_printk(KERN_DEBUG, "Setting flags for stat...\n");

fs/ecryptfs/inode.c

@@ -289,6 +289,7 @@ static struct dentry *ecryptfs_lookup(struct inode *dir, struct dentry *dentry,
 	char *encoded_name;
 	unsigned int encoded_namelen;
 	struct ecryptfs_crypt_stat *crypt_stat = NULL;
+	struct ecryptfs_mount_crypt_stat *mount_crypt_stat;
 	char *page_virt = NULL;
 	struct inode *lower_inode;
 	u64 file_size;
@@ -388,8 +389,18 @@ static struct dentry *ecryptfs_lookup(struct inode *dir, struct dentry *dentry,
 		}
 		crypt_stat->flags |= ECRYPTFS_METADATA_IN_XATTR;
 	}
+	mount_crypt_stat = &ecryptfs_superblock_to_private(
+		dentry->d_sb)->mount_crypt_stat;
+	if (mount_crypt_stat->flags & ECRYPTFS_ENCRYPTED_VIEW_ENABLED) {
+		if (crypt_stat->flags & ECRYPTFS_METADATA_IN_XATTR)
+			file_size = (crypt_stat->header_extent_size
+				     + i_size_read(lower_dentry->d_inode));
+		else
+			file_size = i_size_read(lower_dentry->d_inode);
+	} else {
 		memcpy(&file_size, page_virt, sizeof(file_size));
 		file_size = be64_to_cpu(file_size);
+	}
 	i_size_write(dentry->d_inode, (loff_t)file_size);
 	kmem_cache_free(ecryptfs_header_cache_2, page_virt);
 	goto out;

fs/ecryptfs/mmap.c

@@ -260,6 +260,33 @@ out:
 		ClearPageUptodate(page);
 	return rc;
 }
+/**
+ *   Header Extent:
+ *     Octets 0-7:        Unencrypted file size (big-endian)
+ *     Octets 8-15:       eCryptfs special marker
+ *     Octets 16-19:      Flags
+ *      Octet 16:         File format version number (between 0 and 255)
+ *      Octets 17-18:     Reserved
+ *      Octet 19:         Bit 1 (lsb): Reserved
+ *                        Bit 2: Encrypted?
+ *                        Bits 3-8: Reserved
+ *     Octets 20-23:      Header extent size (big-endian)
+ *     Octets 24-25:      Number of header extents at front of file
+ *                        (big-endian)
+ *     Octet  26:         Begin RFC 2440 authentication token packet set
+ */
+static void set_header_info(char *page_virt,
+			    struct ecryptfs_crypt_stat *crypt_stat)
+{
+	size_t written;
+	int save_num_header_extents_at_front =
+		crypt_stat->num_header_extents_at_front;
+
+	crypt_stat->num_header_extents_at_front = 1;
+	ecryptfs_write_header_metadata(page_virt + 20, crypt_stat, &written);
+	crypt_stat->num_header_extents_at_front =
+		save_num_header_extents_at_front;
+}
 
 /**
  * ecryptfs_readpage
@@ -289,10 +316,55 @@ static int ecryptfs_readpage(struct file *file, struct page *page)
 					"[%d]\n", rc);
 			goto out;
 		}
+	} else if (crypt_stat->flags & ECRYPTFS_VIEW_AS_ENCRYPTED) {
+		if (crypt_stat->flags & ECRYPTFS_METADATA_IN_XATTR) {
+			int num_pages_in_header_region =
+				(crypt_stat->header_extent_size
+				 / PAGE_CACHE_SIZE);
+
+			if (page->index < num_pages_in_header_region) {
+				char *page_virt;
+
+				page_virt = (char *)kmap(page);
+				if (!page_virt) {
+					rc = -ENOMEM;
+					printk(KERN_ERR "Error mapping page\n");
+					goto out;
+				}
+				memset(page_virt, 0, PAGE_CACHE_SIZE);
+				if (page->index == 0) {
+					rc = ecryptfs_read_xattr_region(
+						page_virt, file->f_path.dentry);
+					set_header_info(page_virt, crypt_stat);
+				}
+				kunmap(page);
+				if (rc) {
+					printk(KERN_ERR "Error reading xattr "
+					       "region\n");
+					goto out;
+				}
+			} else {
+				rc = ecryptfs_do_readpage(
+					file, page,
+					(page->index
+					 - num_pages_in_header_region));
+				if (rc) {
+					printk(KERN_ERR "Error reading page; "
+					       "rc = [%d]\n", rc);
+					goto out;
+				}
+			}
+		} else {
+			rc = ecryptfs_do_readpage(file, page, page->index);
+			if (rc) {
+				printk(KERN_ERR "Error reading page; rc = "
+				       "[%d]\n", rc);
+				goto out;
+			}
+		}
 	} else {
 		rc = ecryptfs_decrypt_page(file, page);
 		if (rc) {
-
 			ecryptfs_printk(KERN_ERR, "Error decrypting page; "
 					"rc = [%d]\n", rc);
 			goto out;