[PATCH 1/1] eCryptfs: Initialize empty lower files when opening them

[Colin King]

From: Colin Ian King <colin.king at canonical.com>

Historically, eCryptfs has only initialized lower files in the
ecryptfs_create() path. Lower file initialization is the act of writing
the cryptographic metadata from the inode's crypt_stat to the header of
the file. The ecryptfs_open() path already expects that metadata to be
in the header of the file.

A number of users have reported empty lower files in beneath their
eCryptfs mounts. Most of the causes for those empty files being left
around have been addressed, but the presence of empty files causes
problems due to the lack of proper cryptographic metadata.

To transparently solve this problem, this patch initializes empty lower
files in the ecryptfs_open() error path. If the metadata is unreadable
due to the lower inode size being 0, plaintext passthrough support is
not in use, and the metadata is stored in the header of the file (as
opposed to the user.ecryptfs extended attribute), the lower file will be
initialized.

The number of nested conditionals in ecryptfs_open() was getting out of
hand, so a helper function was created. To avoid the same nested
conditional problem, the conditional logic was reversed inside of the
helper function.

https://launchpad.net/bugs/911507

Signed-off-by: Tyler Hicks <tyhicks at canonical.com>
Cc: John Johansen <john.johansen at canonical.com>
Cc: Colin Ian King <colin.king at canonical.com>
(backport from upstream commit e3ccaa9761200952cc269b1f4b7d7bb77a5e071b)
Signed-off-by: Colin Ian King <colin.king at canonical.com>
---
 fs/ecryptfs/ecryptfs_kernel.h |    1 +
 fs/ecryptfs/file.c            |   71 ++++++++++++++++++++++++++---------------
 fs/ecryptfs/inode.c           |    2 +-
 3 files changed, 47 insertions(+), 27 deletions(-)

diff --git a/fs/ecryptfs/ecryptfs_kernel.h b/fs/ecryptfs/ecryptfs_kernel.h
index 4181136..f3a94b5 100644
--- a/fs/ecryptfs/ecryptfs_kernel.h
+++ b/fs/ecryptfs/ecryptfs_kernel.h
@@ -630,6 +630,7 @@ int ecryptfs_interpose(struct dentry *hidden_dentry,
 		       struct dentry *this_dentry, struct super_block *sb,
 		       u32 flags);
 void ecryptfs_i_size_init(const char *page_virt, struct inode *inode);
+int ecryptfs_initialize_file(struct dentry *ecryptfs_dentry);
 int ecryptfs_lookup_and_interpose_lower(struct dentry *ecryptfs_dentry,
 					struct dentry *lower_dentry,
 					struct inode *ecryptfs_dir_inode,
diff --git a/fs/ecryptfs/file.c b/fs/ecryptfs/file.c
index 502b09f..669dd8d 100644
--- a/fs/ecryptfs/file.c
+++ b/fs/ecryptfs/file.c
@@ -141,6 +141,48 @@ out:
 
 struct kmem_cache *ecryptfs_file_info_cache;
 
+static int read_or_initialize_metadata(struct dentry *dentry)
+{
+	struct inode *inode = dentry->d_inode;
+	struct ecryptfs_mount_crypt_stat *mount_crypt_stat;
+	struct ecryptfs_crypt_stat *crypt_stat;
+	int rc;
+
+	crypt_stat = &ecryptfs_inode_to_private(inode)->crypt_stat;
+	mount_crypt_stat = &ecryptfs_superblock_to_private(
+						inode->i_sb)->mount_crypt_stat;
+	mutex_lock(&crypt_stat->cs_mutex);
+
+	if (crypt_stat->flags & ECRYPTFS_POLICY_APPLIED &&
+	    crypt_stat->flags & ECRYPTFS_KEY_VALID) {
+		rc = 0;
+		goto out;
+	}
+
+	rc = ecryptfs_read_metadata(dentry);
+	if (!rc)
+		goto out;
+
+	if (mount_crypt_stat->flags & ECRYPTFS_PLAINTEXT_PASSTHROUGH_ENABLED) {
+		crypt_stat->flags &= ~(ECRYPTFS_I_SIZE_INITIALIZED
+				       | ECRYPTFS_ENCRYPTED);
+		rc = 0;
+		goto out;
+	}
+
+	if (!(mount_crypt_stat->flags & ECRYPTFS_XATTR_METADATA_ENABLED) &&
+	    !i_size_read(ecryptfs_inode_to_lower(inode))) {
+		rc = ecryptfs_initialize_file(dentry);
+		if (!rc)
+			goto out;
+	}
+
+	rc = -EIO;
+out:
+	mutex_unlock(&crypt_stat->cs_mutex);
+	return rc;
+}
+
 /**
  * ecryptfs_open
  * @inode: inode speciying file to open
@@ -218,32 +260,9 @@ static int ecryptfs_open(struct inode *inode, struct file *file)
 		rc = 0;
 		goto out;
 	}
-	mutex_lock(&crypt_stat->cs_mutex);
-	if (!(crypt_stat->flags & ECRYPTFS_POLICY_APPLIED)
-	    || !(crypt_stat->flags & ECRYPTFS_KEY_VALID)) {
-		rc = ecryptfs_read_metadata(ecryptfs_dentry);
-		if (rc) {
-			ecryptfs_printk(KERN_DEBUG,
-					"Valid headers not found\n");
-			if (!(mount_crypt_stat->flags
-			      & ECRYPTFS_PLAINTEXT_PASSTHROUGH_ENABLED)) {
-				rc = -EIO;
-				printk(KERN_WARNING "Either the lower file "
-				       "is not in a valid eCryptfs format, "
-				       "or the key could not be retrieved. "
-				       "Plaintext passthrough mode is not "
-				       "enabled; returning -EIO\n");
-				mutex_unlock(&crypt_stat->cs_mutex);
-				goto out_free;
-			}
-			rc = 0;
-			crypt_stat->flags &= ~(ECRYPTFS_I_SIZE_INITIALIZED
-						| ECRYPTFS_ENCRYPTED);
-			mutex_unlock(&crypt_stat->cs_mutex);
-			goto out;
-		}
-	}
-	mutex_unlock(&crypt_stat->cs_mutex);
+	rc = read_or_initialize_metadata(ecryptfs_dentry);
+	if (rc)
+		goto out_free;
 	ecryptfs_printk(KERN_DEBUG, "inode w/ addr = [0x%p], i_ino = [0x%.16x] "
 			"size: [0x%.16x]\n", inode, inode->i_ino,
 			i_size_read(inode));
diff --git a/fs/ecryptfs/inode.c b/fs/ecryptfs/inode.c
index 3c1dbc0..7d6574c 100644
--- a/fs/ecryptfs/inode.c
+++ b/fs/ecryptfs/inode.c
@@ -173,7 +173,7 @@ static int grow_file(struct dentry *ecryptfs_dentry)
  *
  * Returns zero on success
  */
-static int ecryptfs_initialize_file(struct dentry *ecryptfs_dentry)
+int ecryptfs_initialize_file(struct dentry *ecryptfs_dentry)
 {
 	struct ecryptfs_crypt_stat *crypt_stat =
 		&ecryptfs_inode_to_private(ecryptfs_dentry->d_inode)->crypt_stat;
-- 
1.7.9.5