1 files changed, 247 insertions, 0 deletions
diff --git a/fs/f2fs/verity.c b/fs/f2fs/verity.c
new file mode 100644
index 000000000000..a401ef72bc82
--- /dev/null
+++ b/fs/f2fs/verity.c
@@ -0,0 +1,247 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * fs/f2fs/verity.c: fs-verity support for f2fs
+ *
+ * Copyright 2019 Google LLC
+ */
+
+/*
+ * Implementation of fsverity_operations for f2fs.
+ *
+ * Like ext4, f2fs stores the verity metadata (Merkle tree and
+ * fsverity_descriptor) past the end of the file, starting at the first 64K
+ * boundary beyond i_size.  This approach works because (a) verity files are
+ * readonly, and (b) pages fully beyond i_size aren't visible to userspace but
+ * can be read/written internally by f2fs with only some relatively small
+ * changes to f2fs.  Extended attributes cannot be used because (a) f2fs limits
+ * the total size of an inode's xattr entries to 4096 bytes, which wouldn't be
+ * enough for even a single Merkle tree block, and (b) f2fs encryption doesn't
+ * encrypt xattrs, yet the verity metadata *must* be encrypted when the file is
+ * because it contains hashes of the plaintext data.
+ *
+ * Using a 64K boundary rather than a 4K one keeps things ready for
+ * architectures with 64K pages, and it doesn't necessarily waste space on-disk
+ * since there can be a hole between i_size and the start of the Merkle tree.
+ */
+
+#include <linux/f2fs_fs.h>
+
+#include "f2fs.h"
+#include "xattr.h"
+
+static inline loff_t f2fs_verity_metadata_pos(const struct inode *inode)
+{
+	return round_up(inode->i_size, 65536);
+}
+
+/*
+ * Read some verity metadata from the inode.  __vfs_read() can't be used because
+ * we need to read beyond i_size.
+ */
+static int pagecache_read(struct inode *inode, void *buf, size_t count,
+			  loff_t pos)
+{
+	while (count) {
+		size_t n = min_t(size_t, count,
+				 PAGE_SIZE - offset_in_page(pos));
+		struct page *page;
+		void *addr;
+
+		page = read_mapping_page(inode->i_mapping, pos >> PAGE_SHIFT,
+					 NULL);
+		if (IS_ERR(page))
+			return PTR_ERR(page);
+
+		addr = kmap_atomic(page);
+		memcpy(buf, addr + offset_in_page(pos), n);
+		kunmap_atomic(addr);
+
+		put_page(page);
+
+		buf += n;
+		pos += n;
+		count -= n;
+	}
+	return 0;
+}
+
+/*
+ * Write some verity metadata to the inode for FS_IOC_ENABLE_VERITY.
+ * kernel_write() can't be used because the file descriptor is readonly.
+ */
+static int pagecache_write(struct inode *inode, const void *buf, size_t count,
+			   loff_t pos)
+{
+	if (pos + count > inode->i_sb->s_maxbytes)
+		return -EFBIG;
+
+	while (count) {
+		size_t n = min_t(size_t, count,
+				 PAGE_SIZE - offset_in_page(pos));
+		struct page *page;
+		void *fsdata;
+		void *addr;
+		int res;
+
+		res = pagecache_write_begin(NULL, inode->i_mapping, pos, n, 0,
+					    &page, &fsdata);
+		if (res)
+			return res;
+
+		addr = kmap_atomic(page);
+		memcpy(addr + offset_in_page(pos), buf, n);
+		kunmap_atomic(addr);
+
+		res = pagecache_write_end(NULL, inode->i_mapping, pos, n, n,
+					  page, fsdata);
+		if (res < 0)
+			return res;
+		if (res != n)
+			return -EIO;
+
+		buf += n;
+		pos += n;
+		count -= n;
+	}
+	return 0;
+}
+
+/*
+ * Format of f2fs verity xattr.  This points to the location of the verity
+ * descriptor within the file data rather than containing it directly because
+ * the verity descriptor *must* be encrypted when f2fs encryption is used.  But,
+ * f2fs encryption does not encrypt xattrs.
+ */
+struct fsverity_descriptor_location {
+	__le32 version;
+	__le32 size;
+	__le64 pos;
+};
+
+static int f2fs_begin_enable_verity(struct file *filp)
+{
+	struct inode *inode = file_inode(filp);
+	int err;
+
+	if (f2fs_verity_in_progress(inode))
+		return -EBUSY;
+
+	if (f2fs_is_atomic_file(inode) || f2fs_is_volatile_file(inode))
+		return -EOPNOTSUPP;
+
+	/*
+	 * Since the file was opened readonly, we have to initialize the quotas
+	 * here and not rely on ->open() doing it.  This must be done before
+	 * evicting the inline data.
+	 */
+	err = dquot_initialize(inode);
+	if (err)
+		return err;
+
+	err = f2fs_convert_inline_inode(inode);
+	if (err)
+		return err;
+
+	set_inode_flag(inode, FI_VERITY_IN_PROGRESS);
+	return 0;
+}
+
+static int f2fs_end_enable_verity(struct file *filp, const void *desc,
+				  size_t desc_size, u64 merkle_tree_size)
+{
+	struct inode *inode = file_inode(filp);
+	u64 desc_pos = f2fs_verity_metadata_pos(inode) + merkle_tree_size;
+	struct fsverity_descriptor_location dloc = {
+		.version = cpu_to_le32(1),
+		.size = cpu_to_le32(desc_size),
+		.pos = cpu_to_le64(desc_pos),
+	};
+	int err = 0;
+
+	if (desc != NULL) {
+		/* Succeeded; write the verity descriptor. */
+		err = pagecache_write(inode, desc, desc_size, desc_pos);
+
+		/* Write all pages before clearing FI_VERITY_IN_PROGRESS. */
+		if (!err)
+			err = filemap_write_and_wait(inode->i_mapping);
+	}
+
+	/* If we failed, truncate anything we wrote past i_size. */
+	if (desc == NULL || err)
+		f2fs_truncate(inode);
+
+	clear_inode_flag(inode, FI_VERITY_IN_PROGRESS);
+
+	if (desc != NULL && !err) {
+		err = f2fs_setxattr(inode, F2FS_XATTR_INDEX_VERITY,
+				    F2FS_XATTR_NAME_VERITY, &dloc, sizeof(dloc),
+				    NULL, XATTR_CREATE);
+		if (!err) {
+			file_set_verity(inode);
+			f2fs_set_inode_flags(inode);
+			f2fs_mark_inode_dirty_sync(inode, true);
+		}
+	}
+	return err;
+}
+
+static int f2fs_get_verity_descriptor(struct inode *inode, void *buf,
+				      size_t buf_size)
+{
+	struct fsverity_descriptor_location dloc;
+	int res;
+	u32 size;
+	u64 pos;
+
+	/* Get the descriptor location */
+	res = f2fs_getxattr(inode, F2FS_XATTR_INDEX_VERITY,
+			    F2FS_XATTR_NAME_VERITY, &dloc, sizeof(dloc), NULL);
+	if (res < 0 && res != -ERANGE)
+		return res;
+	if (res != sizeof(dloc) || dloc.version != cpu_to_le32(1)) {
+		f2fs_warn(F2FS_I_SB(inode), "unknown verity xattr format");
+		return -EINVAL;
+	}
+	size = le32_to_cpu(dloc.size);
+	pos = le64_to_cpu(dloc.pos);
+
+	/* Get the descriptor */
+	if (pos + size < pos || pos + size > inode->i_sb->s_maxbytes ||
+	    pos < f2fs_verity_metadata_pos(inode) || size > INT_MAX) {
+		f2fs_warn(F2FS_I_SB(inode), "invalid verity xattr");
+		return -EFSCORRUPTED;
+	}
+	if (buf_size) {
+		if (size > buf_size)
+			return -ERANGE;
+		res = pagecache_read(inode, buf, size, pos);
+		if (res)
+			return res;
+	}
+	return size;
+}
+
+static struct page *f2fs_read_merkle_tree_page(struct inode *inode,
+					       pgoff_t index)
+{
+	index += f2fs_verity_metadata_pos(inode) >> PAGE_SHIFT;
+
+	return read_mapping_page(inode->i_mapping, index, NULL);
+}
+
+static int f2fs_write_merkle_tree_block(struct inode *inode, const void *buf,
+					u64 index, int log_blocksize)
+{
+	loff_t pos = f2fs_verity_metadata_pos(inode) + (index << log_blocksize);
+
+	return pagecache_write(inode, buf, 1 << log_blocksize, pos);
+}
+
+const struct fsverity_operations f2fs_verityops = {
+	.begin_enable_verity	= f2fs_begin_enable_verity,
+	.end_enable_verity	= f2fs_end_enable_verity,
+	.get_verity_descriptor	= f2fs_get_verity_descriptor,
+	.read_merkle_tree_page	= f2fs_read_merkle_tree_page,
+	.write_merkle_tree_block = f2fs_write_merkle_tree_block,
+};