eCryptfs: read_write.c routines

Add a set of functions through which all I/O to lower files is consolidated.
This patch adds a new inode_info reference to a persistent lower file for each
eCryptfs inode; another patch later in this series will set that up.  This
persistent lower file is what the read_write.c functions use to call
vfs_read() and vfs_write() on the lower filesystem, so even when reads and
writes come in through aops->readpage and aops->writepage, we can satisfy them
without resorting to direct access to the lower inode's address space.
Several function declarations are going to be changing with this patchset.
For now, in order to keep from breaking the build, I am putting dummy
parameters in for those functions.

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>

1 files changed, 359 insertions, 0 deletions

diff --git a/fs/ecryptfs/read_write.c b/fs/ecryptfs/read_write.c
new file mode 100644
index 000000000000..e59c94add127
--- /dev/null
+++ b/fs/ecryptfs/read_write.c
@@ -0,0 +1,359 @@
+/**
+ * eCryptfs: Linux filesystem encryption layer
+ *
+ * Copyright (C) 2007 International Business Machines Corp.
+ *   Author(s): Michael A. Halcrow <mahalcro@us.ibm.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License as
+ * published by the Free Software Foundation; either version 2 of the
+ * License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
+ * 02111-1307, USA.
+ */
+
+#include <linux/fs.h>
+#include <linux/pagemap.h>
+#include "ecryptfs_kernel.h"
+
+/**
+ * ecryptfs_write_lower
+ * @ecryptfs_inode: The eCryptfs inode
+ * @data: Data to write
+ * @offset: Byte offset in the lower file to which to write the data
+ * @size: Number of bytes from @data to write at @offset in the lower
+ *        file
+ *
+ * Write data to the lower file.
+ *
+ * Returns zero on success; non-zero on error
+ */
+int ecryptfs_write_lower(struct inode *ecryptfs_inode, char *data,
+			 loff_t offset, size_t size)
+{
+	struct ecryptfs_inode_info *inode_info;
+	ssize_t octets_written;
+	mm_segment_t fs_save;
+	int rc = 0;
+
+	inode_info = ecryptfs_inode_to_private(ecryptfs_inode);
+	mutex_lock(&inode_info->lower_file_mutex);
+	BUG_ON(!inode_info->lower_file);
+	inode_info->lower_file->f_pos = offset;
+	fs_save = get_fs();
+	set_fs(get_ds());
+	octets_written = vfs_write(inode_info->lower_file, data, size,
+				   &inode_info->lower_file->f_pos);
+	set_fs(fs_save);
+	if (octets_written < 0) {
+		printk(KERN_ERR "%s: octets_written = [%td]; "
+		       "expected [%td]\n", __FUNCTION__, octets_written, size);
+		rc = -EINVAL;
+	}
+	mutex_unlock(&inode_info->lower_file_mutex);
+	mark_inode_dirty_sync(ecryptfs_inode);
+	return rc;
+}
+
+/**
+ * ecryptfs_write_lower_page_segment
+ * @ecryptfs_inode: The eCryptfs inode
+ * @page_for_lower: The page containing the data to be written to the
+ *                  lower file
+ * @offset_in_page: The offset in the @page_for_lower from which to
+ *                  start writing the data
+ * @size: The amount of data from @page_for_lower to write to the
+ *        lower file
+ *
+ * Determines the byte offset in the file for the given page and
+ * offset within the page, maps the page, and makes the call to write
+ * the contents of @page_for_lower to the lower inode.
+ *
+ * Returns zero on success; non-zero otherwise
+ */
+int ecryptfs_write_lower_page_segment(struct inode *ecryptfs_inode,
+				      struct page *page_for_lower,
+				      size_t offset_in_page, size_t size)
+{
+	char *virt;
+	loff_t offset;
+	int rc;
+
+	offset = (page_for_lower->index << PAGE_CACHE_SHIFT) + offset_in_page;
+	virt = kmap(page_for_lower);
+	rc = ecryptfs_write_lower(ecryptfs_inode, virt, offset, size);
+	kunmap(page_for_lower);
+	return rc;
+}
+
+/**
+ * ecryptfs_write
+ * @ecryptfs_file: The eCryptfs file into which to write
+ * @data: Virtual address where data to write is located
+ * @offset: Offset in the eCryptfs file at which to begin writing the
+ *          data from @data
+ * @size: The number of bytes to write from @data
+ *
+ * Write an arbitrary amount of data to an arbitrary location in the
+ * eCryptfs inode page cache. This is done on a page-by-page, and then
+ * by an extent-by-extent, basis; individual extents are encrypted and
+ * written to the lower page cache (via VFS writes). This function
+ * takes care of all the address translation to locations in the lower
+ * filesystem; it also handles truncate events, writing out zeros
+ * where necessary.
+ *
+ * Returns zero on success; non-zero otherwise
+ */
+int ecryptfs_write(struct file *ecryptfs_file, char *data, loff_t offset,
+		   size_t size)
+{
+	struct page *ecryptfs_page;
+	char *ecryptfs_page_virt;
+	u64 ecryptfs_file_size = i_size_read(ecryptfs_file->f_dentry->d_inode);
+	loff_t data_offset = 0;
+	loff_t pos;
+	int rc = 0;
+
+	if (offset > ecryptfs_file_size)
+		pos = ecryptfs_file_size;
+	else
+		pos = offset;
+	while (pos < (offset + size)) {
+		pgoff_t ecryptfs_page_idx = (pos >> PAGE_CACHE_SHIFT);
+		size_t start_offset_in_page = (pos & ~PAGE_CACHE_MASK);
+		size_t num_bytes = (PAGE_CACHE_SIZE - start_offset_in_page);
+		size_t total_remaining_bytes = ((offset + size) - pos);
+
+		if (num_bytes > total_remaining_bytes)
+			num_bytes = total_remaining_bytes;
+		if (pos < offset) {
+			size_t total_remaining_zeros = (offset - pos);
+
+			if (num_bytes > total_remaining_zeros)
+				num_bytes = total_remaining_zeros;
+		}
+		ecryptfs_page = ecryptfs_get1page(ecryptfs_file,
+						  ecryptfs_page_idx);
+		if (IS_ERR(ecryptfs_page)) {
+			rc = PTR_ERR(ecryptfs_page);
+			printk(KERN_ERR "%s: Error getting page at "
+			       "index [%ld] from eCryptfs inode "
+			       "mapping; rc = [%d]\n", __FUNCTION__,
+			       ecryptfs_page_idx, rc);
+			goto out;
+		}
+		if (start_offset_in_page) {
+			/* Read in the page from the lower
+			 * into the eCryptfs inode page cache,
+			 * decrypting */
+			if ((rc = ecryptfs_decrypt_page(NULL, /* placeholder for git-bisect */
+							ecryptfs_page))) {
+				printk(KERN_ERR "%s: Error decrypting "
+				       "page; rc = [%d]\n",
+				       __FUNCTION__, rc);
+				page_cache_release(ecryptfs_page);
+				goto out;
+			}
+		}
+		ecryptfs_page_virt = kmap_atomic(ecryptfs_page, KM_USER0);
+		if (pos >= offset) {
+			memcpy(((char *)ecryptfs_page_virt
+				+ start_offset_in_page),
+			       (data + data_offset), num_bytes);
+			data_offset += num_bytes;
+		} else {
+			/* We are extending past the previous end of the file.
+			 * Fill in zero values up to the start of where we
+			 * will be writing data. */
+			memset(((char *)ecryptfs_page_virt
+				+ start_offset_in_page), 0, num_bytes);
+		}
+		kunmap_atomic(ecryptfs_page_virt, KM_USER0);
+		flush_dcache_page(ecryptfs_page);
+		rc = ecryptfs_encrypt_page(NULL /* placeholder for git-bisect */);
+		if (rc) {
+			printk(KERN_ERR "%s: Error encrypting "
+			       "page; rc = [%d]\n", __FUNCTION__, rc);
+			page_cache_release(ecryptfs_page);
+			goto out;
+		}
+		page_cache_release(ecryptfs_page);
+		pos += num_bytes;
+	}
+	if ((offset + size) > ecryptfs_file_size) {
+		i_size_write(ecryptfs_file->f_dentry->d_inode, (offset + size));
+		rc = ecryptfs_write_inode_size_to_metadata(NULL, NULL, NULL,
+							   NULL, 0); /* placeholders for git-bisect */
+		if (rc) {
+			printk(KERN_ERR	"Problem with "
+			       "ecryptfs_write_inode_size_to_metadata; "
+			       "rc = [%d]\n", rc);
+			goto out;
+		}
+	}
+out:
+	return rc;
+}
+
+/**
+ * ecryptfs_read_lower
+ * @data: The read data is stored here by this function
+ * @offset: Byte offset in the lower file from which to read the data
+ * @size: Number of bytes to read from @offset of the lower file and
+ *        store into @data
+ * @ecryptfs_inode: The eCryptfs inode
+ *
+ * Read @size bytes of data at byte offset @offset from the lower
+ * inode into memory location @data.
+ *
+ * Returns zero on success; non-zero on error
+ */
+int ecryptfs_read_lower(char *data, loff_t offset, size_t size,
+			struct inode *ecryptfs_inode)
+{
+	struct ecryptfs_inode_info *inode_info =
+		ecryptfs_inode_to_private(ecryptfs_inode);
+	ssize_t octets_read;
+	mm_segment_t fs_save;
+	size_t i;
+	int rc = 0;
+
+	mutex_lock(&inode_info->lower_file_mutex);
+	BUG_ON(!inode_info->lower_file);
+	inode_info->lower_file->f_pos = offset;
+	fs_save = get_fs();
+	set_fs(get_ds());
+	octets_read = vfs_read(inode_info->lower_file, data, size,
+			       &inode_info->lower_file->f_pos);
+	set_fs(fs_save);
+	if (octets_read < 0) {
+		printk(KERN_ERR "%s: octets_read = [%td]; "
+		       "expected [%td]\n", __FUNCTION__, octets_read, size);
+		rc = -EINVAL;
+	}
+	mutex_unlock(&inode_info->lower_file_mutex);
+	for (i = 0; i < size; i += PAGE_CACHE_SIZE) {
+		struct page *data_page;
+
+		data_page = virt_to_page(data + i);
+		flush_dcache_page(data_page);
+		if (rc)
+			ClearPageUptodate(data_page);
+		else
+			SetPageUptodate(data_page);
+	}
+	return rc;
+}
+
+/**
+ * ecryptfs_read_lower_page_segment
+ * @page_for_ecryptfs: The page into which data for eCryptfs will be
+ *                     written
+ * @offset_in_page: Offset in @page_for_ecryptfs from which to start
+ *                  writing
+ * @size: The number of bytes to write into @page_for_ecryptfs
+ * @ecryptfs_inode: The eCryptfs inode
+ *
+ * Determines the byte offset in the file for the given page and
+ * offset within the page, maps the page, and makes the call to read
+ * the contents of @page_for_ecryptfs from the lower inode.
+ *
+ * Returns zero on success; non-zero otherwise
+ */
+int ecryptfs_read_lower_page_segment(struct page *page_for_ecryptfs,
+				     pgoff_t page_index,
+				     size_t offset_in_page, size_t size,
+				     struct inode *ecryptfs_inode)
+{
+	char *virt;
+	loff_t offset;
+	int rc;
+
+	offset = ((page_index << PAGE_CACHE_SHIFT) + offset_in_page);
+	virt = kmap(page_for_ecryptfs);
+	rc = ecryptfs_read_lower(virt, offset, size, ecryptfs_inode);
+	kunmap(page_for_ecryptfs);
+	return rc;
+}
+
+/**
+ * ecryptfs_read
+ * @data: The virtual address into which to write the data read (and
+ *        possibly decrypted) from the lower file
+ * @offset: The offset in the decrypted view of the file from which to
+ *          read into @data
+ * @size: The number of bytes to read into @data
+ * @ecryptfs_file: The eCryptfs file from which to read
+ *
+ * Read an arbitrary amount of data from an arbitrary location in the
+ * eCryptfs page cache. This is done on an extent-by-extent basis;
+ * individual extents are decrypted and read from the lower page
+ * cache (via VFS reads). This function takes care of all the
+ * address translation to locations in the lower filesystem.
+ *
+ * Returns zero on success; non-zero otherwise
+ */
+int ecryptfs_read(char *data, loff_t offset, size_t size,
+		  struct file *ecryptfs_file)
+{
+	struct page *ecryptfs_page;
+	char *ecryptfs_page_virt;
+	u64 ecryptfs_file_size = i_size_read(ecryptfs_file->f_dentry->d_inode);
+	loff_t data_offset = 0;
+	loff_t pos;
+	int rc = 0;
+
+	if ((offset + size) > ecryptfs_file_size) {
+		rc = -EINVAL;
+		printk(KERN_ERR "%s: Attempt to read data past the end of the "
+			"file; offset = [%lld]; size = [%td]; "
+		       "ecryptfs_file_size = [%lld]\n",
+		       __FUNCTION__, offset, size, ecryptfs_file_size);
+		goto out;
+	}
+	pos = offset;
+	while (pos < (offset + size)) {
+		pgoff_t ecryptfs_page_idx = (pos >> PAGE_CACHE_SHIFT);
+		size_t start_offset_in_page = (pos & ~PAGE_CACHE_MASK);
+		size_t num_bytes = (PAGE_CACHE_SIZE - start_offset_in_page);
+		size_t total_remaining_bytes = ((offset + size) - pos);
+
+		if (num_bytes > total_remaining_bytes)
+			num_bytes = total_remaining_bytes;
+		ecryptfs_page = ecryptfs_get1page(ecryptfs_file,
+						  ecryptfs_page_idx);
+		if (IS_ERR(ecryptfs_page)) {
+			rc = PTR_ERR(ecryptfs_page);
+			printk(KERN_ERR "%s: Error getting page at "
+			       "index [%ld] from eCryptfs inode "
+			       "mapping; rc = [%d]\n", __FUNCTION__,
+			       ecryptfs_page_idx, rc);
+			goto out;
+		}
+		rc = ecryptfs_decrypt_page(NULL /* placeholder for git-bisect */, ecryptfs_page);
+		if (rc) {
+			printk(KERN_ERR "%s: Error decrypting "
+			       "page; rc = [%d]\n", __FUNCTION__, rc);
+			page_cache_release(ecryptfs_page);
+			goto out;
+		}
+		ecryptfs_page_virt = kmap_atomic(ecryptfs_page, KM_USER0);
+		memcpy((data + data_offset),
+		       ((char *)ecryptfs_page_virt + start_offset_in_page),
+		       num_bytes);
+		kunmap_atomic(ecryptfs_page_virt, KM_USER0);
+		page_cache_release(ecryptfs_page);
+		pos += num_bytes;
+		data_offset += num_bytes;
+	}
+out:
+	return rc;
+}