fscrypt: new helper function - fscrypt_file_open()

Add a helper function which prepares to open a regular file which may be
encrypted.  It handles setting up the file's encryption key, then
checking that the file's encryption policy matches that of its parent
directory (if the parent directory is encrypted).  It may be set as the
->open() method or it can be called from another ->open() method.

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/Makefile b/fs/crypto/Makefile
index 9f6607f17b53bfeba9d7940380928439f4e5b466..cb496989a6b693fe0b13cb2c737a7643288d5bc9 100644 (file)
--- a/fs/crypto/Makefile
+++ b/fs/crypto/Makefile
@@ -1,4 +1,4 @@
 obj-$(CONFIG_FS_ENCRYPTION)    += fscrypto.o
 
-fscrypto-y := crypto.o fname.o policy.o keyinfo.o
+fscrypto-y := crypto.o fname.o hooks.o keyinfo.o policy.o
 fscrypto-$(CONFIG_BLOCK) += bio.o

diff --git a/fs/crypto/hooks.c b/fs/crypto/hooks.c
new file mode 100644 (file)
index 0000000..069088e
--- /dev/null
+++ b/fs/crypto/hooks.c
@@ -0,0 +1,49 @@
+/*
+ * fs/crypto/hooks.c
+ *
+ * Encryption hooks for higher-level filesystem operations.
+ */
+
+#include <linux/ratelimit.h>
+#include "fscrypt_private.h"
+
+/**
+ * fscrypt_file_open - prepare to open a possibly-encrypted regular file
+ * @inode: the inode being opened
+ * @filp: the struct file being set up
+ *
+ * Currently, an encrypted regular file can only be opened if its encryption key
+ * is available; access to the raw encrypted contents is not supported.
+ * Therefore, we first set up the inode's encryption key (if not already done)
+ * and return an error if it's unavailable.
+ *
+ * We also verify that if the parent directory (from the path via which the file
+ * is being opened) is encrypted, then the inode being opened uses the same
+ * encryption policy.  This is needed as part of the enforcement that all files
+ * in an encrypted directory tree use the same encryption policy, as a
+ * protection against certain types of offline attacks.  Note that this check is
+ * needed even when opening an *unencrypted* file, since it's forbidden to have
+ * an unencrypted file in an encrypted directory.
+ *
+ * Return: 0 on success, -ENOKEY if the key is missing, or another -errno code
+ */
+int fscrypt_file_open(struct inode *inode, struct file *filp)
+{
+       int err;
+       struct dentry *dir;
+
+       err = fscrypt_require_key(inode);
+       if (err)
+               return err;
+
+       dir = dget_parent(file_dentry(filp));
+       if (IS_ENCRYPTED(d_inode(dir)) &&
+           !fscrypt_has_permitted_context(d_inode(dir), inode)) {
+               pr_warn_ratelimited("fscrypt: inconsistent encryption contexts: %lu/%lu",
+                                   d_inode(dir)->i_ino, inode->i_ino);
+               err = -EPERM;
+       }
+       dput(dir);
+       return err;
+}
+EXPORT_SYMBOL_GPL(fscrypt_file_open);

diff --git a/include/linux/fscrypt_notsupp.h b/include/linux/fscrypt_notsupp.h
index ca5bd51a376a18be75fc5eabef8aac18f0e75400..ea26d4c609dff7a200b13c654cf16fe5c48eeae3 100644 (file)
--- a/include/linux/fscrypt_notsupp.h
+++ b/include/linux/fscrypt_notsupp.h
@@ -178,4 +178,13 @@ static inline int fscrypt_zeroout_range(const struct inode *inode, pgoff_t lblk,
        return -EOPNOTSUPP;
 }
 
+/* hooks.c */
+
+static inline int fscrypt_file_open(struct inode *inode, struct file *filp)
+{
+       if (IS_ENCRYPTED(inode))
+               return -EOPNOTSUPP;
+       return 0;
+}
+
 #endif /* _LINUX_FSCRYPT_NOTSUPP_H */

diff --git a/include/linux/fscrypt_supp.h b/include/linux/fscrypt_supp.h
index 2c969e526ed09a33516d35b1df22c681d793b9c6..0551352156e4cfda7a021f47bf1a78e759691ff4 100644 (file)
--- a/include/linux/fscrypt_supp.h
+++ b/include/linux/fscrypt_supp.h
@@ -144,4 +144,7 @@ extern void fscrypt_pullback_bio_page(struct page **, bool);
 extern int fscrypt_zeroout_range(const struct inode *, pgoff_t, sector_t,
                                 unsigned int);
 
+/* hooks.c */
+extern int fscrypt_file_open(struct inode *inode, struct file *filp);
+
 #endif /* _LINUX_FSCRYPT_SUPP_H */