From: Eric Biggers <ebiggers@xxxxxxxxxx>
Filesystems also have duplicate code to support ->get_link() on
encrypted symlinks. Factor it out into a new function
fscrypt_get_symlink(). It takes in the contents of the encrypted
symlink on-disk and provides the target (decrypted or encoded) that
should be returned from ->get_link().
Signed-off-by: Eric Biggers <ebiggers@xxxxxxxxxx>
---
fs/crypto/hooks.c | 73 +++++++++++++++++++++++++++++++++++++++++
include/linux/fscrypt_notsupp.h | 8 +++++
include/linux/fscrypt_supp.h | 3 ++
3 files changed, 84 insertions(+)
diff --git a/fs/crypto/hooks.c b/fs/crypto/hooks.c
index 483e87d40f03..0f103a5cb1aa 100644
--- a/fs/crypto/hooks.c
+++ b/fs/crypto/hooks.c
@@ -196,3 +196,76 @@ int __fscrypt_encrypt_symlink(struct inode *inode, const char *target,
return 0;
}
EXPORT_SYMBOL_GPL(__fscrypt_encrypt_symlink);
+
+/**
+ * fscrypt_get_symlink - get the target of an encrypted symlink
+ * @inode: the symlink inode
+ * @caddr: the on-disk contents of the symlink
+ * @max_size: size of @caddr buffer
+ * @done: if successful, will be set up to free the returned target
+ *
+ * If the symlink's encryption key is available, we decrypt its target.
+ * Otherwise, we encode its target for presentation.
+ *
+ * This may sleep, so the filesystem must have dropped out of RCU mode already.
+ *
+ * Return: the presentable symlink target or an ERR_PTR()
+ */
+const char *fscrypt_get_symlink(struct inode *inode, const void *caddr,
+ unsigned int max_size,
+ struct delayed_call *done)
+{
+ const struct fscrypt_symlink_data *sd;
+ struct fscrypt_str cstr, pstr;
+ int err;
+
+ /* This is for encrypted symlinks only */
+ if (WARN_ON(!IS_ENCRYPTED(inode)))
+ return ERR_PTR(-EINVAL);
+
+ /*
+ * Try to set up the symlink's encryption key, but we can continue
+ * regardless of whether the key is available or not.
+ */
+ err = fscrypt_get_encryption_info(inode);
+ if (err)
+ return ERR_PTR(err);
+
+ /*
+ * For historical reasons, encrypted symlink targets are prefixed with
+ * the ciphertext length, even though this is redundant with i_size.
+ */
+
+ if (max_size < sizeof(*sd))
+ return ERR_PTR(-EUCLEAN);
+ sd = caddr;
+ cstr.name = (unsigned char *)sd->encrypted_path;
+ cstr.len = le16_to_cpu(sd->len);
+
+ if (cstr.len == 0)
+ return ERR_PTR(-EUCLEAN);
+
+ if (cstr.len + sizeof(*sd) - 1 > max_size)
+ return ERR_PTR(-EUCLEAN);
+
+ err = fscrypt_fname_alloc_buffer(inode, cstr.len, &pstr);
+ if (err)
+ return ERR_PTR(err);
+
+ err = fscrypt_fname_disk_to_usr(inode, 0, 0, &cstr, &pstr);
+ if (err)
+ goto err_kfree;
+
+ err = -EUCLEAN;
+ if (pstr.name[0] == '\0')
+ goto err_kfree;
+
+ pstr.name[pstr.len] = '\0';
+ set_delayed_call(done, kfree_link, pstr.name);
+ return pstr.name;
+
+err_kfree:
+ kfree(pstr.name);
+ return ERR_PTR(err);
+}
+EXPORT_SYMBOL_GPL(fscrypt_get_symlink);
diff --git a/include/linux/fscrypt_notsupp.h b/include/linux/fscrypt_notsupp.h
index 02ec0aa894d8..dd106640c6ea 100644
--- a/include/linux/fscrypt_notsupp.h
+++ b/include/linux/fscrypt_notsupp.h
@@ -239,4 +239,12 @@ static inline int __fscrypt_encrypt_symlink(struct inode *inode,
return -EOPNOTSUPP;
}
+static inline const char *fscrypt_get_symlink(struct inode *inode,
+ const void *caddr,
+ unsigned int max_size,
+ struct delayed_call *done)
+{
+ return ERR_PTR(-EOPNOTSUPP);
+}
+
#endif /* _LINUX_FSCRYPT_NOTSUPP_H */
diff --git a/include/linux/fscrypt_supp.h b/include/linux/fscrypt_supp.h
index 7e0b67ccd816..dc2babf3f7d3 100644
--- a/include/linux/fscrypt_supp.h
+++ b/include/linux/fscrypt_supp.h
@@ -211,5 +211,8 @@ extern int __fscrypt_prepare_symlink(struct inode *dir, unsigned int len,
extern int __fscrypt_encrypt_symlink(struct inode *inode, const char *target,
unsigned int len,
struct fscrypt_str *disk_link);
+extern const char *fscrypt_get_symlink(struct inode *inode, const void *caddr,
+ unsigned int max_size,
+ struct delayed_call *done);
#endif /* _LINUX_FSCRYPT_SUPP_H */
--
2.15.1
