[PATCH v5 04/18] fscrypt: add extent-based encryption

[Sweet Tea Dorminy <sweettea-kernel@dorminy.me>]

Some filesystems need to encrypt data based on extents, rather than on
inodes, due to features incompatible with inode-based encryption. For
instance, btrfs can have multiple inodes referencing a single block of
data, and moves logical data blocks to different physical locations on
disk in the background; these two features mean traditional inode-based
file contents encryption will not work for btrfs.

This change introduces fscrypt_extent_context objects, in analogy to
existing context objects based on inodes. For a filesystem which opts to
use extent-based encryption, a new hook provides a new
fscrypt_extent_context. During file content encryption/decryption, the
existing fscrypt_context object provides key information, while the new
fscrypt_extent_context provides nonce information. For filename encryption,
the existing IV generation methods are still used, since filenames are
not stored in extents.

Only direct key policies are allowed, but any encryption mode is allowed
within that constraint.

Signed-off-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
---
 fs/crypto/crypto.c          | 20 +++++++++--
 fs/crypto/fscrypt_private.h | 25 +++++++++++++-
 fs/crypto/inline_crypt.c    | 28 ++++++++++++----
 fs/crypto/policy.c          | 66 +++++++++++++++++++++++++++++++++++++
 include/linux/fscrypt.h     | 47 ++++++++++++++++++++++++++
 5 files changed, 176 insertions(+), 10 deletions(-)

diff --git a/fs/crypto/crypto.c b/fs/crypto/crypto.c
index 7fe5979fbea2..08b495dc5c0c 100644
--- a/fs/crypto/crypto.c
+++ b/fs/crypto/crypto.c
@@ -81,8 +81,22 @@ void fscrypt_generate_iv(union fscrypt_iv *iv, u64 lblk_num,
 			 const struct fscrypt_info *ci)
 {
 	u8 flags = fscrypt_policy_flags(&ci->ci_policy);
+	struct inode *inode = ci->ci_inode;
+	const struct fscrypt_operations *s_cop = inode->i_sb->s_cop;
 
-	memset(iv, 0, ci->ci_mode->ivsize);
+	memset(iv, 0, sizeof(*iv));
+	if (s_cop->get_extent_context && lblk_num != U64_MAX) {
+		size_t extent_offset;
+		union fscrypt_extent_context ctx;
+		int ret;
+
+		ret = fscrypt_get_extent_context(inode, lblk_num, &ctx,
+						 &extent_offset, NULL);
+		WARN_ON_ONCE(ret);
+		memcpy(iv->raw, ctx.v1.iv.raw, sizeof(*iv));
+		iv->lblk_num += cpu_to_le64(extent_offset);
+		return;
+	}
 
 	/*
 	 * Filename encryption. For inode-based policies, filenames are
@@ -93,8 +107,8 @@ void fscrypt_generate_iv(union fscrypt_iv *iv, u64 lblk_num,
 
 	if (flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_64) {
 		WARN_ON_ONCE(lblk_num > U32_MAX);
-		WARN_ON_ONCE(ci->ci_inode->i_ino > U32_MAX);
-		lblk_num |= (u64)ci->ci_inode->i_ino << 32;
+		WARN_ON_ONCE(inode->i_ino > U32_MAX);
+		lblk_num |= (u64)inode->i_ino << 32;
 	} else if (flags & FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32) {
 		WARN_ON_ONCE(lblk_num > U32_MAX);
 		lblk_num = (u32)(ci->ci_hashed_ino + lblk_num);
diff --git a/fs/crypto/fscrypt_private.h b/fs/crypto/fscrypt_private.h
index d5f68a0c5d15..9c4cae2580de 100644
--- a/fs/crypto/fscrypt_private.h
+++ b/fs/crypto/fscrypt_private.h
@@ -280,7 +280,6 @@ fscrypt_msg(const struct inode *inode, const char *level, const char *fmt, ...);
 	fscrypt_msg((inode), KERN_ERR, fmt, ##__VA_ARGS__)
 
 #define FSCRYPT_MAX_IV_SIZE	32
-
 union fscrypt_iv {
 	struct {
 		/* logical block number within the file */
@@ -293,6 +292,27 @@ union fscrypt_iv {
 	__le64 dun[FSCRYPT_MAX_IV_SIZE / sizeof(__le64)];
 };
 
+
+/*
+ * fscrypt_extent_context - the encryption context for an extent
+ *
+ * For filesystems that support extent encryption, this context provides the
+ * necessary randomly-initialized IV in order to encrypt/decrypt the data
+ * stored in the extent. It is stored alongside each extent, and is
+ * insufficient to decrypt the extent: the extent's owning inode(s) provide the
+ * policy information (including key identifier) necessary to decrypt.
+ */
+struct fscrypt_extent_context_v1 {
+	u8 version;
+	union fscrypt_iv iv;
+} __packed;
+
+union fscrypt_extent_context {
+	u8 version;
+	struct fscrypt_extent_context_v1 v1;
+};
+
+
 void fscrypt_generate_iv(union fscrypt_iv *iv, u64 lblk_num,
 			 const struct fscrypt_info *ci);
 
@@ -662,5 +682,8 @@ int fscrypt_policy_from_context(union fscrypt_policy *policy_u,
 				const union fscrypt_context *ctx_u,
 				int ctx_size);
 const union fscrypt_policy *fscrypt_policy_to_inherit(struct inode *dir);
+int fscrypt_get_extent_context(const struct inode *inode, u64 lblk_num,
+			       union fscrypt_extent_context *ctx,
+			       size_t *extent_offset, size_t *extent_length);
 
 #endif /* _FSCRYPT_PRIVATE_H */
diff --git a/fs/crypto/inline_crypt.c b/fs/crypto/inline_crypt.c
index cea8b14007e6..6adb72c52ce2 100644
--- a/fs/crypto/inline_crypt.c
+++ b/fs/crypto/inline_crypt.c
@@ -460,6 +460,7 @@ EXPORT_SYMBOL_GPL(fscrypt_dio_supported);
  */
 u64 fscrypt_limit_io_blocks(const struct inode *inode, u64 lblk, u64 nr_blocks)
 {
+	const struct fscrypt_operations *s_cop = inode->i_sb->s_cop;
 	const struct fscrypt_info *ci;
 	u32 dun;
 
@@ -470,14 +471,29 @@ u64 fscrypt_limit_io_blocks(const struct inode *inode, u64 lblk, u64 nr_blocks)
 		return nr_blocks;
 
 	ci = inode->i_crypt_info;
-	if (!(fscrypt_policy_flags(&ci->ci_policy) &
-	      FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32))
-		return nr_blocks;
 
-	/* With IV_INO_LBLK_32, the DUN can wrap around from U32_MAX to 0. */
+	if (s_cop->get_extent_context) {
+		size_t extent_offset, extent_length;
+		int ret = fscrypt_get_extent_context(inode, lblk, NULL,
+						     &extent_offset,
+						     &extent_length);
+		if (ret < 0) {
+			WARN_ON_ONCE(ret < 0);
+			return 1;
+		}
+		return extent_length - extent_offset;
+	}
 
-	dun = ci->ci_hashed_ino + lblk;
+	if ((fscrypt_policy_flags(&ci->ci_policy) &
+	      FSCRYPT_POLICY_FLAG_IV_INO_LBLK_32)) {
+		/*
+		 * With IV_INO_LBLK_32, the DUN can wrap around from U32_MAX to
+		 * 0.
+		 */
+		dun = ci->ci_hashed_ino + lblk;
+		return min_t(u64, nr_blocks, (u64)U32_MAX + 1 - dun);
+	}
 
-	return min_t(u64, nr_blocks, (u64)U32_MAX + 1 - dun);
+	return nr_blocks;
 }
 EXPORT_SYMBOL_GPL(fscrypt_limit_io_blocks);
diff --git a/fs/crypto/policy.c b/fs/crypto/policy.c
index 715870d4e530..a874afcf9652 100644
--- a/fs/crypto/policy.c
+++ b/fs/crypto/policy.c
@@ -222,6 +222,10 @@ static bool fscrypt_supported_v2_policy(const struct fscrypt_policy_v2 *policy,
 		return false;
 	}
 
+	if (inode->i_sb->s_cop->get_extent_context &&
+	    !(policy->flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY))
+		return false;
+
 	if ((policy->flags & FSCRYPT_POLICY_FLAG_DIRECT_KEY) &&
 	    !supported_direct_key_modes(inode, policy->contents_encryption_mode,
 					policy->filenames_encryption_mode))
@@ -786,6 +790,68 @@ int fscrypt_set_context(struct inode *inode, void *fs_data)
 }
 EXPORT_SYMBOL_GPL(fscrypt_set_context);
 
+/**
+ * fscrypt_get_extent_context() - Get the fscrypt extent context for a location
+ *
+ * @inode: an inode associated with the extent
+ * @lblk_num: a logical block number within the inode owned by the extent
+ * @ctx: a pointer to return the context found (may be NULL)
+ * @extent_offset: a pointer to return the offset of @lblk_num within the
+ *                 extent (may be NULL)
+ * @extent_length: a pointer to return the length of the extent found (may be
+ *                 NULL)
+ *
+ * Return: 0 on success, -errno on failure
+ */
+int fscrypt_get_extent_context(const struct inode *inode, u64 lblk_num,
+			       union fscrypt_extent_context *ctx,
+			       size_t *extent_offset, size_t *extent_length)
+{
+	int ret;
+	int ctxsize = (ctx == NULL ? 0 : sizeof(*ctx));
+
+	if (!IS_ENCRYPTED(inode))
+		return -ENODATA;
+
+	ret = inode->i_sb->s_cop->get_extent_context(inode, lblk_num, ctx,
+						     ctxsize, extent_offset,
+						     extent_length);
+	if (ret == ctxsize && (!ctx || ctx->version == 1))
+		return 0;
+	if (ret >= 0)
+		return -EINVAL;
+	return ret;
+}
+EXPORT_SYMBOL_GPL(fscrypt_get_extent_context);
+
+/**
+ * fscrypt_set_extent_context() - Set an extent's fscrypt context
+ *
+ * @inode: an inode to which the extent belongs
+ * @lblk_num: the offset into the inode at which the extent starts
+ * @extent: private data referring to the extent, given by the FS and passed
+ *          to ->set_extent_context()
+ *
+ * This should be called after fscrypt_prepare_new_inode(), generally during a
+ * filesystem transaction.  Everything here must be %GFP_NOFS-safe.
+ *
+ * Return: 0 on success, -errno on failure
+ */
+int fscrypt_set_extent_context(struct inode *inode, u64 lblk_num, void *extent)
+{
+	union fscrypt_extent_context ctx;
+
+	if (!IS_ENCRYPTED(inode))
+		return -ENODATA;
+
+	ctx.v1.version = 1;
+	get_random_bytes(ctx.v1.nonce, FSCRYPT_FILE_NONCE_SIZE);
+
+	return inode->i_sb->s_cop->set_extent_context(extent,
+						      &ctx, sizeof(ctx));
+}
+EXPORT_SYMBOL_GPL(fscrypt_set_extent_context);
+
 /**
  * fscrypt_parse_test_dummy_encryption() - parse the test_dummy_encryption mount option
  * @param: the mount option
diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
index 0069f92ee3da..402fc0ca7abf 100644
--- a/include/linux/fscrypt.h
+++ b/include/linux/fscrypt.h
@@ -94,6 +94,13 @@ struct fscrypt_nokey_name {
 /* Maximum value for the third parameter of fscrypt_operations.set_context(). */
 #define FSCRYPT_SET_CONTEXT_MAX_SIZE	40
 
+/*
+ * Maximum value for the third parameter of
+ * fscrypt_operations.set_extent_context(). Update if fscrypt_private.h:
+ * FSCRYPT_MAX_IVSIZE changes
+ */
+#define FSCRYPT_EXTENT_CONTEXT_MAX_SIZE	33
+
 #ifdef CONFIG_FS_ENCRYPTION
 
 /*
@@ -150,6 +157,39 @@ struct fscrypt_operations {
 	int (*set_context)(struct inode *inode, const void *ctx, size_t len,
 			   void *fs_data);
 
+	/*
+	 * Get the fscrypt extent context for a given inode and lblk number.
+	 *
+	 * @inode: the inode to which the extent belongs
+	 * @lblk_num: the block number within the file whose extent is being
+	 *            queried
+	 * @ctx: the buffer into which to get the context (may be NULL)
+	 * @len: the length of the @ctx buffer in bytes
+	 * @extent_offset: a pointer to return the offset of @lblk_num within
+	 *                 the extent whose context is returned (may be NULL)
+	 * @extent_length: a pointer to return the total length of the extent
+	 *                 whose context was found (may be NULL)
+	 *
+	 * Return: On success, returns the length of the context in bytes,
+	 * which may be less than @len. On failure, returns -ENODATA if the
+	 * extent doesn't have a context, -ERANGE if the context is longer
+	 * than @len, or another -errno code.
+	 */
+	int (*get_extent_context)(const struct inode *inode, u64 lblk_num,
+				  void *ctx, size_t len,
+				  size_t *extent_offset, size_t *extent_length);
+
+	/*
+	 * Set the fscrypt extent context for an extent.
+	 *
+	 * @extent: an opaque pointer to the filesystem's extent object
+	 * @ctx: the buffer containing the extent context to set
+	 * @len: the length of the @ctx buffer in bytes
+	 *
+	 * Return: 0 on success, -errno on failure.
+	 */
+	int (*set_extent_context)(void *extent, void *ctx, size_t len);
+
 	/*
 	 * Get the dummy fscrypt policy in use on the filesystem (if any).
 	 *
@@ -322,6 +362,7 @@ int fscrypt_ioctl_get_nonce(struct file *filp, void __user *arg);
 int fscrypt_has_permitted_context(struct inode *parent, struct inode *child);
 int fscrypt_context_for_new_inode(void *ctx, struct inode *inode);
 int fscrypt_set_context(struct inode *inode, void *fs_data);
+int fscrypt_set_extent_context(struct inode *inode, u64 offset, void *extent);
 
 struct fscrypt_dummy_policy {
 	const union fscrypt_policy *policy;
@@ -531,6 +572,12 @@ static inline int fscrypt_set_context(struct inode *inode, void *fs_data)
 	return -EOPNOTSUPP;
 }
 
+static inline int fscrypt_set_extent_context(struct inode *inode, u64 offset,
+					     void *extent)
+{
+	return -EOPNOTSUPP;
+}
+
 struct fscrypt_dummy_policy {
 };
 
-- 
2.37.3