[PATCH v2 11/11] fscrypt: new helper function - fscrypt_prepare_setattr()
From: Eric Biggers <hidden>
Date: 2017-10-09 19:19:12
Also in:
linux-f2fs-devel, linux-fscrypt, linux-fsdevel
Subsystem:
fscrypt: file system level encryption support, the rest · Maintainers:
Eric Biggers, Theodore Y. Ts'o, Jaegeuk Kim, Linus Torvalds
From: Eric Biggers <redacted> Introduce a helper function for filesystems to call when processing ->setattr() on a possibly-encrypted inode. It handles enforcing that an encrypted file can only be truncated if its encryption key is available. Acked-by: Dave Chinner <redacted> Signed-off-by: Eric Biggers <redacted> --- include/linux/fscrypt.h | 25 +++++++++++++++++++++++++ 1 file changed, 25 insertions(+)
diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
index 2327859c8cd2..53437bfdfcbc 100644
--- a/include/linux/fscrypt.h
+++ b/include/linux/fscrypt.h@@ -265,4 +265,29 @@ static inline int fscrypt_prepare_lookup(struct inode *dir, return 0; } +/** + * fscrypt_prepare_setattr - prepare to change a possibly-encrypted inode's attributes + * @dentry: dentry through which the inode is being changed + * @attr: attributes to change + * + * Prepare for ->setattr() on a possibly-encrypted inode. On an encrypted file, + * most attribute changes are allowed even without the encryption key. However, + * without the encryption key we do have to forbid truncates. This is needed + * because the size being truncated to may not be a multiple of the filesystem + * block size, and in that case we'd have to decrypt the final block, zero the + * portion past i_size, and re-encrypt it. (We *could* allow truncating to a + * filesystem block boundary, but it's simpler to just forbid all truncates --- + * and we already forbid all other contents modifications without the key.) + * + * Return: 0 on success, -ENOKEY if the key is missing, or another -errno code + * if a problem occurred while setting up the encryption key. + */ +static inline int fscrypt_prepare_setattr(struct dentry *dentry, + struct iattr *attr) +{ + if (attr->ia_valid & ATTR_SIZE) + return fscrypt_require_key(d_inode(dentry)); + return 0; +} + #endif /* _LINUX_FSCRYPT_H */
--
2.14.2.920.gcf0c67979c-goog