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Date:	Thu,  2 Apr 2015 18:10:57 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Ext4 Developers List <linux-ext4@...r.kernel.org>
Cc:	jaegeuk@...nel.org, mhalcrow@...gle.com,
	Theodore Ts'o <tytso@....edu>,
	Uday Savagaonkar <savagaon@...gle.com>
Subject: [PATCH 20/22] ext4 crypto: Add symlink encryption

Change-Id: Ic92ebe4c615721650ccaf16b3175c2f4e931af2d
Signed-off-by: Uday Savagaonkar <savagaon@...gle.com>
Signed-off-by: Theodore Ts'o <tytso@....edu>
---
 fs/ext4/ext4_crypto.h |  20 ++++++++++
 fs/ext4/namei.c       |  63 +++++++++++++++++++++++++++---
 fs/ext4/symlink.c     | 104 +++++++++++++++++++++++++++++++++++++++++++++++++-
 3 files changed, 180 insertions(+), 7 deletions(-)

diff --git a/fs/ext4/ext4_crypto.h b/fs/ext4/ext4_crypto.h
index 68e95d8..4597530 100644
--- a/fs/ext4/ext4_crypto.h
+++ b/fs/ext4/ext4_crypto.h
@@ -117,4 +117,24 @@ struct ext4_fname_crypto_ctx {
 	unsigned ctfm_key_is_ready : 1;
 };
 
+/**
+ * For encrypted symlinks, the ciphertext length is stored at the beginning
+ * of the string in little-endian format.
+ */
+struct ext4_encrypted_symlink_data {
+	__le32 len;
+	char encrypted_path[1];
+} __attribute__((__packed__));
+
+/**
+ * This function is used to calculate the disk space required to
+ * store a filename of length l in encrypted symlink format.
+ */
+static inline u32 encrypted_symlink_data_len(u32 l)
+{
+	return ((l + EXT4_CRYPTO_BLOCK_SIZE - 1) / EXT4_CRYPTO_BLOCK_SIZE)
+		* EXT4_CRYPTO_BLOCK_SIZE
+		+ sizeof(struct ext4_encrypted_symlink_data) - 1;
+}
+
 #endif	/* _EXT4_CRYPTO_H */
diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index 80a3979..57db793 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -3198,14 +3198,31 @@ static int ext4_symlink(struct inode *dir,
 	struct inode *inode;
 	int l, err, retries = 0;
 	int credits;
+	bool encryption_required = false;
+#ifdef CONFIG_EXT4_FS_ENCRYPTION
+	int l2;
+	struct ext4_fname_crypto_ctx *ctx = NULL;
+	struct qstr istr;
+	struct ext4_str ostr;
+	struct ext4_encrypted_symlink_data *sd = NULL;
+	struct ext4_sb_info *sbi = EXT4_SB(dir->i_sb);
+#endif
 
-	l = strlen(symname)+1;
+	l = strlen(symname) + 1;
+#ifdef CONFIG_EXT4_FS_ENCRYPTION
+	l2 = encrypted_symlink_data_len(l - 1);
+	encryption_required = (ext4_encrypted_inode(dir) ||
+			       unlikely(sbi->s_mount_flags &
+					EXT4_MF_TEST_DUMMY_ENCRYPTION));
+	if (encryption_required && l2 > dir->i_sb->s_blocksize)
+#else
 	if (l > dir->i_sb->s_blocksize)
+#endif
 		return -ENAMETOOLONG;
 
 	dquot_initialize(dir);
 
-	if (l > EXT4_N_BLOCKS * 4) {
+	if ((l > EXT4_N_BLOCKS * 4) || encryption_required) {
 		/*
 		 * For non-fast symlinks, we just allocate inode and put it on
 		 * orphan list in the first transaction => we need bitmap,
@@ -3233,7 +3250,7 @@ retry:
 	if (IS_ERR(inode))
 		goto out_stop;
 
-	if (l > EXT4_N_BLOCKS * 4) {
+	if ((l > EXT4_N_BLOCKS * 4) || encryption_required) {
 		inode->i_op = &ext4_symlink_inode_operations;
 		ext4_set_aops(inode);
 		/*
@@ -3251,9 +3268,40 @@ retry:
 		ext4_journal_stop(handle);
 		if (err)
 			goto err_drop_inode;
-		err = __page_symlink(inode, symname, l, 1);
-		if (err)
-			goto err_drop_inode;
+		if (!encryption_required) {
+			err = __page_symlink(inode, symname, l, 1);
+			if (err)
+				goto err_drop_inode;
+		}
+#ifdef CONFIG_EXT4_FS_ENCRYPTION
+		else {
+			sd = kmalloc(l2 + 1, GFP_NOFS);
+			if (!sd) {
+				err = -ENOMEM;
+				goto err_drop_inode;
+			}
+			sd->encrypted_path[l2] = '\0';
+			err = ext4_inherit_context(dir, inode);
+			ctx = ext4_get_fname_crypto_ctx(
+				inode, inode->i_sb->s_blocksize);
+			if (IS_ERR_OR_NULL(ctx)) {
+				/* We just set the policy, so ctx should
+				   not be NULL */
+				err = (ctx == NULL) ? -EIO : PTR_ERR(ctx);
+				goto err_drop_inode;
+			}
+			istr.name = (const unsigned char *) symname;
+			istr.len = l - 1;
+			ostr.name = sd->encrypted_path;
+			err = ext4_fname_usr_to_disk(ctx, &istr, &ostr);
+			ext4_put_fname_crypto_ctx(&ctx);
+			if (err < 0)
+				goto err_drop_inode;
+			sd->len = cpu_to_le32(ostr.len);
+			err = __page_symlink(inode, (char *)sd, l2 + 1, 1);
+
+		}
+#endif
 		/*
 		 * Now inode is being linked into dir (EXT4_DATA_TRANS_BLOCKS
 		 * + EXT4_INDEX_EXTRA_TRANS_BLOCKS), inode is also modified
@@ -3293,6 +3341,9 @@ out_stop:
 err_drop_inode:
 	unlock_new_inode(inode);
 	iput(inode);
+#ifdef CONFIG_EXT4_FS_ENCRYPTION
+	kfree(sd);
+#endif
 	return err;
 }
 
diff --git a/fs/ext4/symlink.c b/fs/ext4/symlink.c
index ff37119..d788891 100644
--- a/fs/ext4/symlink.c
+++ b/fs/ext4/symlink.c
@@ -22,9 +22,106 @@
 #include <linux/namei.h>
 #include "ext4.h"
 #include "xattr.h"
+#include "ext4_crypto.h"
 
+#ifdef CONFIG_EXT4_FS_ENCRYPTION
 static void *ext4_follow_link(struct dentry *dentry, struct nameidata *nd)
 {
+	struct page *cpage = NULL;
+	char *caddr, *paddr;
+	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(inode->i_size, (loff_t) PAGE_SIZE-1);
+	int res;
+	u32 plen, plen2;
+
+	ctx = ext4_get_fname_crypto_ctx(inode, inode->i_sb->s_blocksize);
+	if (IS_ERR(ctx))
+		return ctx;
+
+	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;
+
+	if (!ctx) {
+		/* Symlink is unencrypted */
+		plen = strnlen((char *)caddr, inode->i_sb->s_blocksize);
+		plen2 = (plen < inode->i_sb->s_blocksize) ? plen + 1 : plen;
+		paddr = kmalloc(plen2, GFP_NOFS);
+		if (!paddr) {
+			ext4_put_fname_crypto_ctx(&ctx);
+			kunmap(cpage);
+			page_cache_release(cpage);
+			return ERR_PTR(-ENOMEM);
+		}
+		memcpy(paddr, caddr, plen);
+		if (plen < inode->i_sb->s_blocksize)
+			paddr[plen] = '\0';
+	} else {
+		/* 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)
+			> inode->i_sb->s_blocksize) {
+			/* Symlink data on the disk is corrupted */
+			kunmap(cpage);
+			page_cache_release(cpage);
+			return ERR_PTR(-EIO);
+		}
+		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) {
+			ext4_put_fname_crypto_ctx(&ctx);
+			kunmap(cpage);
+			page_cache_release(cpage);
+			return ERR_PTR(-ENOMEM);
+		}
+		pstr.name = paddr;
+		res = _ext4_fname_disk_to_usr(ctx, &cstr, &pstr);
+		if (res < 0) {
+			ext4_put_fname_crypto_ctx(&ctx);
+			kunmap(cpage);
+			page_cache_release(cpage);
+			kfree(paddr);
+			return ERR_PTR(res);
+		}
+		/* Null-terminate the name */
+		if (res <= plen)
+			paddr[res] = '\0';
+	}
+	nd_set_link(nd, paddr);
+	ext4_put_fname_crypto_ctx(&ctx);
+	return cpage;
+}
+
+static void ext4_put_link(struct dentry *dentry, struct nameidata *nd,
+			  void *cookie)
+{
+	struct page *page = cookie;
+	char *buf = nd_get_link(nd);
+
+	if (page) {
+		kunmap(page);
+		page_cache_release(page);
+	}
+	if (buf) {
+		nd_set_link(nd, NULL);
+		kfree(buf);
+	}
+}
+#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;
@@ -32,8 +129,13 @@ 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,
@@ -43,7 +145,7 @@ 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,
-- 
2.3.0

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