fscrypt: new helper function - fscrypt_prepare_link()

Introduce a helper function which prepares to link an inode into a
possibly-encrypted directory.  It handles setting up the target
directory's encryption key, then verifying that the link won't violate
the constraint that all files in an encrypted directory tree use the
same encryption policy.

Acked-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/crypto/hooks.c b/fs/crypto/hooks.c
index 069088e91ea991d3ef3e8d0143e598d9ff7ae047..8b90217320dd121edaf7feb6042d013538062778 100644 (file)
--- a/fs/crypto/hooks.c
+++ b/fs/crypto/hooks.c
@@ -47,3 +47,18 @@ int fscrypt_file_open(struct inode *inode, struct file *filp)
        return err;
 }
 EXPORT_SYMBOL_GPL(fscrypt_file_open);
+
+int __fscrypt_prepare_link(struct inode *inode, struct inode *dir)
+{
+       int err;
+
+       err = fscrypt_require_key(dir);
+       if (err)
+               return err;
+
+       if (!fscrypt_has_permitted_context(dir, inode))
+               return -EPERM;
+
+       return 0;
+}
+EXPORT_SYMBOL_GPL(__fscrypt_prepare_link);

diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
index cc86d49c820d64e69e75d01f56b510d69dd7fa71..6ceb76abd8428c599471e78d4ce6ff36d6d1f6b8 100644 (file)
--- a/include/linux/fscrypt.h
+++ b/include/linux/fscrypt.h
@@ -178,4 +178,31 @@ static inline int fscrypt_require_key(struct inode *inode)
        return 0;
 }
 
+/**
+ * fscrypt_prepare_link - prepare to link an inode into a possibly-encrypted directory
+ * @old_dentry: an existing dentry for the inode being linked
+ * @dir: the target directory
+ * @dentry: negative dentry for the target filename
+ *
+ * A new link can only be added to an encrypted directory if the directory's
+ * encryption key is available --- since otherwise we'd have no way to encrypt
+ * the filename.  Therefore, we first set up the directory's encryption key (if
+ * not already done) and return an error if it's unavailable.
+ *
+ * We also verify that the link will not violate the constraint that all files
+ * in an encrypted directory tree use the same encryption policy.
+ *
+ * Return: 0 on success, -ENOKEY if the directory's encryption key is missing,
+ * -EPERM if the link would result in an inconsistent encryption policy, or
+ * another -errno code.
+ */
+static inline int fscrypt_prepare_link(struct dentry *old_dentry,
+                                      struct inode *dir,
+                                      struct dentry *dentry)
+{
+       if (IS_ENCRYPTED(dir))
+               return __fscrypt_prepare_link(d_inode(old_dentry), dir);
+       return 0;
+}
+
 #endif /* _LINUX_FSCRYPT_H */

diff --git a/include/linux/fscrypt_notsupp.h b/include/linux/fscrypt_notsupp.h
index ea26d4c609dff7a200b13c654cf16fe5c48eeae3..a80917bc21026e3db091c63c5a28cb783e9f608b 100644 (file)
--- a/include/linux/fscrypt_notsupp.h
+++ b/include/linux/fscrypt_notsupp.h
@@ -187,4 +187,10 @@ static inline int fscrypt_file_open(struct inode *inode, struct file *filp)
        return 0;
 }
 
+static inline int __fscrypt_prepare_link(struct inode *inode,
+                                        struct inode *dir)
+{
+       return -EOPNOTSUPP;
+}
+
 #endif /* _LINUX_FSCRYPT_NOTSUPP_H */

diff --git a/include/linux/fscrypt_supp.h b/include/linux/fscrypt_supp.h
index 0551352156e4cfda7a021f47bf1a78e759691ff4..547cdbd04f17090429ae4c3103debc6c602d2824 100644 (file)
--- a/include/linux/fscrypt_supp.h
+++ b/include/linux/fscrypt_supp.h
@@ -146,5 +146,6 @@ extern int fscrypt_zeroout_range(const struct inode *, pgoff_t, sector_t,
 
 /* hooks.c */
 extern int fscrypt_file_open(struct inode *inode, struct file *filp);
+extern int __fscrypt_prepare_link(struct inode *inode, struct inode *dir);
 
 #endif /* _LINUX_FSCRYPT_SUPP_H */