ext4 crypto: add symlink encryption

Signed-off-by: Uday Savagaonkar <savagaon@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

1 files changed, 95 insertions, 1 deletions

diff --git a/fs/ext4/symlink.c b/fs/ext4/symlink.c
index 489b34333ea4..136ca0e911fd 100644
--- a/fs/ext4/symlink.c
+++ b/fs/ext4/symlink.c
@@ -22,8 +22,97 @@
 #include "ext4.h"
 #include "xattr.h"
 
+#ifdef CONFIG_EXT4_FS_ENCRYPTION
 static void *ext4_follow_link(struct dentry *dentry, struct nameidata *nd)
 {
+	struct page *cpage = NULL;
+	char *caddr, *paddr = NULL;
+	struct ext4_str cstr, pstr;
+	struct inode *inode = dentry->d_inode;
+	struct ext4_fname_crypto_ctx *ctx = NULL;
+	struct ext4_encrypted_symlink_data *sd;
+	loff_t size = min_t(loff_t, i_size_read(inode), PAGE_SIZE - 1);
+	int res;
+	u32 plen, max_size = inode->i_sb->s_blocksize;
+
+	if (!ext4_encrypted_inode(inode))
+		return page_follow_link_light(dentry, nd);
+
+	ctx = ext4_get_fname_crypto_ctx(inode, inode->i_sb->s_blocksize);
+	if (IS_ERR(ctx))
+		return ctx;
+
+	if (ext4_inode_is_fast_symlink(inode)) {
+		caddr = (char *) EXT4_I(dentry->d_inode)->i_data;
+		max_size = sizeof(EXT4_I(dentry->d_inode)->i_data);
+	} else {
+		cpage = read_mapping_page(inode->i_mapping, 0, NULL);
+		if (IS_ERR(cpage)) {
+			ext4_put_fname_crypto_ctx(&ctx);
+			return cpage;
+		}
+		caddr = kmap(cpage);
+		caddr[size] = 0;
+	}
+
+	/* Symlink is encrypted */
+	sd = (struct ext4_encrypted_symlink_data *)caddr;
+	cstr.name = sd->encrypted_path;
+	cstr.len  = le32_to_cpu(sd->len);
+	if ((cstr.len +
+	     sizeof(struct ext4_encrypted_symlink_data) - 1) >
+	    max_size) {
+		/* Symlink data on the disk is corrupted */
+		res = -EIO;
+		goto errout;
+	}
+	plen = (cstr.len < EXT4_FNAME_CRYPTO_DIGEST_SIZE*2) ?
+		EXT4_FNAME_CRYPTO_DIGEST_SIZE*2 : cstr.len;
+	paddr = kmalloc(plen + 1, GFP_NOFS);
+	if (!paddr) {
+		res = -ENOMEM;
+		goto errout;
+	}
+	pstr.name = paddr;
+	res = _ext4_fname_disk_to_usr(ctx, &cstr, &pstr);
+	if (res < 0)
+		goto errout;
+	/* Null-terminate the name */
+	if (res <= plen)
+		paddr[res] = '\0';
+	nd_set_link(nd, paddr);
+	ext4_put_fname_crypto_ctx(&ctx);
+	if (cpage) {
+		kunmap(cpage);
+		page_cache_release(cpage);
+	}
+	return NULL;
+errout:
+	ext4_put_fname_crypto_ctx(&ctx);
+	if (cpage) {
+		kunmap(cpage);
+		page_cache_release(cpage);
+	}
+	kfree(paddr);
+	return ERR_PTR(res);
+}
+
+static void ext4_put_link(struct dentry *dentry, struct nameidata *nd,
+			  void *cookie)
+{
+	struct page *page = cookie;
+
+	if (!page) {
+		kfree(nd_get_link(nd));
+	} else {
+		kunmap(page);
+		page_cache_release(page);
+	}
+}
+#endif
+
+static void *ext4_follow_fast_link(struct dentry *dentry, struct nameidata *nd)
+{
 	struct ext4_inode_info *ei = EXT4_I(dentry->d_inode);
 	nd_set_link(nd, (char *) ei->i_data);
 	return NULL;
@@ -31,8 +120,13 @@ static void *ext4_follow_link(struct dentry *dentry, struct nameidata *nd)
 
 const struct inode_operations ext4_symlink_inode_operations = {
 	.readlink	= generic_readlink,
+#ifdef CONFIG_EXT4_FS_ENCRYPTION
+	.follow_link    = ext4_follow_link,
+	.put_link       = ext4_put_link,
+#else
 	.follow_link	= page_follow_link_light,
 	.put_link	= page_put_link,
+#endif
 	.setattr	= ext4_setattr,
 	.setxattr	= generic_setxattr,
 	.getxattr	= generic_getxattr,
@@ -42,7 +136,7 @@ const struct inode_operations ext4_symlink_inode_operations = {
 
 const struct inode_operations ext4_fast_symlink_inode_operations = {
 	.readlink	= generic_readlink,
-	.follow_link	= ext4_follow_link,
+	.follow_link    = ext4_follow_fast_link,
 	.setattr	= ext4_setattr,
 	.setxattr	= generic_setxattr,
 	.getxattr	= generic_getxattr,