ext4 crypto: handle unexpected lack of encryption keys

Fix up attempts by users to try to write to a file when they don't
have access to the encryption key.
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/crypto.c

@@ -104,7 +104,8 @@ struct ext4_crypto_ctx *ext4_get_crypto_ctx(struct inode *inode)
 	unsigned long flags;
 	struct ext4_crypt_info *ci = EXT4_I(inode)->i_crypt_info;
 
-	BUG_ON(ci == NULL);
+	if (ci == NULL)
+		return ERR_PTR(-ENOKEY);
 
 	/*
 	 * We first try getting the ctx from a free list because in

fs/ext4/crypto_policy.c

@@ -183,7 +183,8 @@ int ext4_inherit_context(struct inode *parent, struct inode *child)
 	if (res < 0)
 		return res;
 	ci = EXT4_I(parent)->i_crypt_info;
-	BUG_ON(ci == NULL);
+	if (ci == NULL)
+		return -ENOKEY;
 
 	ctx.format = EXT4_ENCRYPTION_CONTEXT_FORMAT_V1;
 	if (DUMMY_ENCRYPTION_ENABLED(EXT4_SB(parent->i_sb))) {

fs/ext4/file.c

@@ -226,6 +226,8 @@ static int ext4_file_mmap(struct file *file, struct vm_area_struct *vma)
 		int err = ext4_get_encryption_info(inode);
 		if (err)
 			return 0;
+		if (ext4_encryption_info(inode) == NULL)
+			return -ENOKEY;
 	}
 	file_accessed(file);
 	if (IS_DAX(file_inode(file))) {
@@ -278,6 +280,13 @@ static int ext4_file_open(struct inode * inode, struct file * filp)
 			ext4_journal_stop(handle);
 		}
 	}
+	if (ext4_encrypted_inode(inode)) {
+		ret = ext4_get_encryption_info(inode);
+		if (ret)
+			return -EACCES;
+		if (ext4_encryption_info(inode) == NULL)
+			return -ENOKEY;
+	}
 	/*
 	 * Set up the jbd2_inode if we are opening the inode for
 	 * writing and the journal is present
@@ -287,13 +296,7 @@ static int ext4_file_open(struct inode * inode, struct file * filp)
 		if (ret < 0)
 			return ret;
 	}
-	ret = dquot_file_open(inode, filp);
-	if (!ret && ext4_encrypted_inode(inode)) {
-		ret = ext4_get_encryption_info(inode);
-		if (ret)
-			ret = -EACCES;
-	}
-	return ret;
+	return dquot_file_open(inode, filp);
 }
 
 /*