[RFC,06/13] fscrypt: allow load/save of extent contexts

Commit Message

Sweet Tea Dorminy Sept. 2, 2023, 5:54 a.m. UTC

The other half of using per-extent infos is saving and loading them from
disk.

This is the one change which cares about whether a lightweight or
heavyweight extent context is stored on disk. This implements the
lightweight version.

Signed-off-by: Sweet Tea Dorminy <[e-mail]>
---
 fs/crypto/keysetup.c    | 39 +++++++++++++++++++++++++++++++++++++++
 fs/crypto/policy.c      | 22 ++++++++++++++++++++++
 include/linux/fscrypt.h | 19 +++++++++++++++++++
 3 files changed, 80 insertions(+)

Patch

diff --git a/fs/crypto/keysetup.c b/fs/crypto/keysetup.c
index c9c16acf4c9b..90143377cc61 100644
--- a/fs/crypto/keysetup.c
+++ b/fs/crypto/keysetup.c
@@ -1044,6 +1044,45 @@  int fscrypt_prepare_new_extent(struct inode *inode,
 }
 EXPORT_SYMBOL_GPL(fscrypt_prepare_new_extent);
 
+/**
+ * fscrypt_load_extent_info() - load a preexisting extent's fscrypt_extent_info
+ * @inode: the inode to which the extent belongs. Must be encrypted.
+ * @buf: a buffer containing the extent's stored context
+ * @len: the length of the @ctx buffer
+ * @info_ptr: a pointer to return the extent's fscrypt_extent_info into
+ *
+ * This is not %GFP_NOFS safe, so the caller is expected to call
+ * memalloc_nofs_save/restore() if appropriate.
+ *
+ * Return: 0 if successful, or -errno if it fails.
+ */
+int fscrypt_load_extent_info(struct inode *inode, void *buf, size_t len,
+			     struct fscrypt_extent_info **info_ptr)
+{
+	int res;
+	union fscrypt_context ctx;
+	const union fscrypt_policy *policy;
+
+	if (!fscrypt_has_encryption_key(inode))
+		return -EINVAL;
+
+	if (len != FSCRYPT_FILE_NONCE_SIZE) {
+		fscrypt_warn(inode,
+			     "Unrecognized or corrupt encryption context");
+		return -EINVAL;
+	}
+
+	policy = fscrypt_policy_to_inherit(inode);
+	if (policy == NULL)
+		return 0;
+	if (IS_ERR(policy))
+		return PTR_ERR(policy);
+
+	return fscrypt_setup_extent_info(inode, policy, buf,
+					 info_ptr);
+}
+EXPORT_SYMBOL_GPL(fscrypt_load_extent_info);
+
 /**
  * fscrypt_free_extent_info() - free an extent's fscrypt_extent_info
  * @info_ptr: a pointer containing the extent's fscrypt_extent_info pointer.
diff --git a/fs/crypto/policy.c b/fs/crypto/policy.c
index ceb648669832..cfbe83aee847 100644
--- a/fs/crypto/policy.c
+++ b/fs/crypto/policy.c
@@ -763,6 +763,28 @@  int fscrypt_set_context(struct inode *inode, void *fs_data)
 }
 EXPORT_SYMBOL_GPL(fscrypt_set_context);
 
+/**
+ * fscrypt_set_extent_context() - Set the fscrypt extent context for an extent
+ * @ci: info from which to fetch policy and nonce
+ * @ctx: where context should be written
+ * @len: the size of ctx
+ *
+ * Given an fscrypt_extent_info belonging to an extent (generated via
+ * fscrypt_prepare_new_extent()), generate a new context and write it to @ctx.
+ * len is checked to be at least FSCRYPT_EXTENT_CONTEXT_MAX_SIZE bytes.
+ *
+ * Return: size of the resulting context or a negative error code.
+ */
+int fscrypt_set_extent_context(struct fscrypt_extent_info *ci, void *ctx,
+			       size_t len)
+{
+	if (len < FSCRYPT_EXTENT_CONTEXT_MAX_SIZE)
+		return -EINVAL;
+	memcpy(ctx, ci->info.ci_nonce, FSCRYPT_FILE_NONCE_SIZE);
+	return FSCRYPT_FILE_NONCE_SIZE;
+}
+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 cc5de5ec888c..b57fc5645076 100644
--- a/include/linux/fscrypt.h
+++ b/include/linux/fscrypt.h
@@ -57,6 +57,7 @@  struct fscrypt_name {
 
 /* Maximum value for the third parameter of fscrypt_operations.set_context(). */
 #define FSCRYPT_SET_CONTEXT_MAX_SIZE	40
+#define FSCRYPT_EXTENT_CONTEXT_MAX_SIZE	16
 
 #ifdef CONFIG_FS_ENCRYPTION
 
@@ -317,6 +318,8 @@  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 fscrypt_extent_info *info, void *ctx,
+			       size_t len);
 
 struct fscrypt_dummy_policy {
 	const union fscrypt_policy *policy;
@@ -357,6 +360,9 @@  int fscrypt_drop_inode(struct inode *inode);
 int fscrypt_prepare_new_extent(struct inode *inode,
 			       struct fscrypt_extent_info **info_ptr);
 void fscrypt_free_extent_info(struct fscrypt_extent_info **info_ptr);
+int fscrypt_load_extent_info(struct inode *inode, void *buf, size_t len,
+			     struct fscrypt_extent_info **info_ptr);
+
 
 /* fname.c */
 int fscrypt_fname_encrypt(const struct inode *inode, const struct qstr *iname,
@@ -533,6 +539,12 @@  static inline int fscrypt_set_context(struct inode *inode, void *fs_data)
 	return -EOPNOTSUPP;
 }
 
+static inline int fscrypt_set_extent_context(struct fscrypt_info *info,
+					     void *ctx, size_t len)
+{
+	return -EOPNOTSUPP;
+}
+
 struct fscrypt_dummy_policy {
 };
 
@@ -632,6 +644,13 @@  static inline void fscrypt_free_extent_info(struct fscrypt_extent_info **info_pt
 {
 }
 
+static inline int fscrypt_load_extent_info(struct inode *inode, void *buf,
+					   size_t len,
+					   struct fscrypt_info **info_ptr)
+{
+	return -EOPNOTSUPP;
+}
+
  /* fname.c */
 static inline int fscrypt_setup_filename(struct inode *dir,
 					 const struct qstr *iname,