ext4 crypto: reorganize how we store keys in the inode

This is a pretty massive patch which does a number of different things:

1) The per-inode encryption information is now stored in an allocated
   data structure, ext4_crypt_info, instead of directly in the node.
   This reduces the size usage of an in-memory inode when it is not
   using encryption.

2) We drop the ext4_fname_crypto_ctx entirely, and use the per-inode
   encryption structure instead.  This remove an unnecessary memory
   allocation and free for the fname_crypto_ctx as well as allowing us
   to reuse the ctfm in a directory for multiple lookups and file
   creations.

3) We also cache the inode's policy information in the ext4_crypt_info
   structure so we don't have to continually read it out of the
   extended attributes.

4) We now keep the keyring key in the inode's encryption structure
   instead of releasing it after we are done using it to derive the
   per-inode key.  This allows us to test to see if the key has been
   revoked; if it has, we prevent the use of the derived key and free
   it.

5) When an inode is released (or when the derived key is freed), we
   will use memset_explicit() to zero out the derived key, so it's not
   left hanging around in memory.  This implies that when a user logs
   out, it is important to first revoke the key, and then unlink it,
   and then finally, to use "echo 3 > /proc/sys/vm/drop_caches" to
   release any decrypted pages and dcache entries from the system
   caches.

6) All this, and we also shrink the number of lines of code by around
   100.  :-)

Signed-off-by: Theodore Ts'o <tytso@mit.edu>

1 files changed, 13 insertions, 29 deletions

diff --git a/fs/ext4/namei.c b/fs/ext4/namei.c
index b3406434c267..9bed99fdd81a 100644
--- a/fs/ext4/namei.c
+++ b/fs/ext4/namei.c
@@ -607,17 +607,14 @@ static struct stats dx_show_leaf(struct inode *dir,
 				char *name;
 				struct ext4_str fname_crypto_str
 					= {.name = NULL, .len = 0};
-				struct ext4_fname_crypto_ctx *ctx = NULL;
 				int res;
 
 				name  = de->name;
 				len = de->name_len;
-				ctx = ext4_get_fname_crypto_ctx(dir,
-								EXT4_NAME_LEN);
-				if (IS_ERR(ctx)) {
-					printk(KERN_WARNING "Error acquiring"
-					" crypto ctxt--skipping crypto\n");
-					ctx = NULL;
+				res = ext4_setup_fname_crypto(dir);
+				if (res) {
+					printk(KERN_WARNING "Error setting up"
+					       " fname crypto: %d\n", res);
 				}
 				if (ctx == NULL) {
 					/* Directory is not encrypted */
@@ -637,7 +634,6 @@ static struct stats dx_show_leaf(struct inode *dir,
 							"allocating crypto "
 							"buffer--skipping "
 							"crypto\n");
-						ext4_put_fname_crypto_ctx(&ctx);
 						ctx = NULL;
 					}
 					res = ext4_fname_disk_to_usr(ctx, NULL, de,
@@ -658,7 +654,6 @@ static struct stats dx_show_leaf(struct inode *dir,
 					printk("%*.s:(E)%x.%u ", len, name,
 					       h.hash, (unsigned) ((char *) de
 								   - base));
-					ext4_put_fname_crypto_ctx(&ctx);
 					ext4_fname_crypto_free_buffer(
 						&fname_crypto_str);
 				}
@@ -944,7 +939,6 @@ static int htree_dirblock_to_tree(struct file *dir_file,
 	struct buffer_head *bh;
 	struct ext4_dir_entry_2 *de, *top;
 	int err = 0, count = 0;
-	struct ext4_fname_crypto_ctx *ctx = NULL;
 	struct ext4_str fname_crypto_str = {.name = NULL, .len = 0}, tmp_str;
 
 	dxtrace(printk(KERN_INFO "In htree dirblock_to_tree: block %lu\n",
@@ -959,17 +953,15 @@ static int htree_dirblock_to_tree(struct file *dir_file,
 					   EXT4_DIR_REC_LEN(0));
 #ifdef CONFIG_EXT4_FS_ENCRYPTION
 	/* Check if the directory is encrypted */
-	ctx = ext4_get_fname_crypto_ctx(dir, EXT4_NAME_LEN);
-	if (IS_ERR(ctx)) {
-		err = PTR_ERR(ctx);
+	err = ext4_setup_fname_crypto(dir);
+	if (err) {
 		brelse(bh);
 		return err;
 	}
-	if (ctx != NULL) {
-		err = ext4_fname_crypto_alloc_buffer(ctx, EXT4_NAME_LEN,
+	if (ext4_encrypted_inode(dir)) {
+		err = ext4_fname_crypto_alloc_buffer(dir, EXT4_NAME_LEN,
 						     &fname_crypto_str);
 		if (err < 0) {
-			ext4_put_fname_crypto_ctx(&ctx);
 			brelse(bh);
 			return err;
 		}
@@ -990,8 +982,7 @@ static int htree_dirblock_to_tree(struct file *dir_file,
 			continue;
 		if (de->inode == 0)
 			continue;
-		if (ctx == NULL) {
-			/* Directory is not encrypted */
+		if (!ext4_encrypted_inode(dir)) {
 			tmp_str.name = de->name;
 			tmp_str.len = de->name_len;
 			err = ext4_htree_store_dirent(dir_file,
@@ -1001,7 +992,7 @@ static int htree_dirblock_to_tree(struct file *dir_file,
 			int save_len = fname_crypto_str.len;
 
 			/* Directory is encrypted */
-			err = ext4_fname_disk_to_usr(ctx, hinfo, de,
+			err = ext4_fname_disk_to_usr(dir, hinfo, de,
 						     &fname_crypto_str);
 			if (err < 0) {
 				count = err;
@@ -1021,7 +1012,6 @@ static int htree_dirblock_to_tree(struct file *dir_file,
 errout:
 	brelse(bh);
 #ifdef CONFIG_EXT4_FS_ENCRYPTION
-	ext4_put_fname_crypto_ctx(&ctx);
 	ext4_fname_crypto_free_buffer(&fname_crypto_str);
 #endif
 	return count;
@@ -3107,7 +3097,6 @@ static int ext4_symlink(struct inode *dir,
 	}
 
 	if (encryption_required) {
-		struct ext4_fname_crypto_ctx *ctx = NULL;
 		struct qstr istr;
 		struct ext4_str ostr;
 
@@ -3119,19 +3108,14 @@ static int ext4_symlink(struct inode *dir,
 		err = ext4_inherit_context(dir, inode);
 		if (err)
 			goto err_drop_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);
+		err = ext4_setup_fname_crypto(inode);
+		if (err)
 			goto err_drop_inode;
-		}
 		istr.name = (const unsigned char *) symname;
 		istr.len = len;
 		ostr.name = sd->encrypted_path;
 		ostr.len = disk_link.len;
-		err = ext4_fname_usr_to_disk(ctx, &istr, &ostr);
-		ext4_put_fname_crypto_ctx(&ctx);
+		err = ext4_fname_usr_to_disk(inode, &istr, &ostr);
 		if (err < 0)
 			goto err_drop_inode;
 		sd->len = cpu_to_le16(ostr.len);