[PATCH 3/3] eCryptfs: Encrypted passthrough

[Michael Halcrow <mhalcrow@us.ibm.com>]

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>

---

 fs/ecryptfs/crypto.c          |   15 ++++++--
 fs/ecryptfs/ecryptfs_kernel.h |    7 +++-
 fs/ecryptfs/file.c            |   13 ++++++-
 fs/ecryptfs/inode.c           |   15 +++++++-
 fs/ecryptfs/mmap.c            |   74 ++++++++++++++++++++++++++++++++++++++++-
 5 files changed, 113 insertions(+), 11 deletions(-)

996f24f59d4bf43b67fe5aa4d4686bd75f09a73e
diff --git a/fs/ecryptfs/crypto.c b/fs/ecryptfs/crypto.c
index e7f5441..8fbc38c 100644
--- a/fs/ecryptfs/crypto.c
+++ b/fs/ecryptfs/crypto.c
@@ -1258,9 +1258,10 @@ out:
 }
 
 
-static void
-write_header_metadata(char *virt, struct ecryptfs_crypt_stat *crypt_stat,
-		      size_t *written)
+void
+ecryptfs_write_header_metadata(char *virt,
+			       struct ecryptfs_crypt_stat *crypt_stat,
+			       size_t *written)
 {
 	u32 header_extent_size;
 	u16 num_header_extents_at_front;
@@ -1322,7 +1323,8 @@ int ecryptfs_write_headers_virt(char *pa
 	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,
@@ -1608,7 +1610,12 @@ int ecryptfs_read_metadata(struct 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) {
diff --git a/fs/ecryptfs/ecryptfs_kernel.h b/fs/ecryptfs/ecryptfs_kernel.h
index aecca2f..859d31b 100644
--- a/fs/ecryptfs/ecryptfs_kernel.h
+++ b/fs/ecryptfs/ecryptfs_kernel.h
@@ -578,7 +578,7 @@ ssize_t ecryptfs_getxattr(struct dentry 
 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,
@@ -601,6 +601,9 @@ int ecryptfs_send_connector(char *data, 
 			    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 */
diff --git a/fs/ecryptfs/file.c b/fs/ecryptfs/file.c
index f22c3a7..652ed77 100644
--- a/fs/ecryptfs/file.c
+++ b/fs/ecryptfs/file.c
@@ -250,6 +250,17 @@ static int ecryptfs_open(struct inode *i
 	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 *i
 	}
 	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");
diff --git a/fs/ecryptfs/inode.c b/fs/ecryptfs/inode.c
index 6b45b29..bbc1b4f 100644
--- a/fs/ecryptfs/inode.c
+++ b/fs/ecryptfs/inode.c
@@ -289,6 +289,7 @@ static struct dentry *ecryptfs_lookup(st
 	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(st
 		}
 		crypt_stat->flags |= ECRYPTFS_METADATA_IN_XATTR;
 	}
-	memcpy(&file_size, page_virt, sizeof(file_size));
-	file_size = be64_to_cpu(file_size);
+	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;
diff --git a/fs/ecryptfs/mmap.c b/fs/ecryptfs/mmap.c
index ba3650d..3386014 100644
--- a/fs/ecryptfs/mmap.c
+++ b/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
 					"[%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;
-- 
1.3.3