f2fs: require key for truncate(2) of encrypted file

Currently, filesystems allow truncate(2) on an encrypted file without
the encryption key.  However, it's impossible to correctly handle the
case where the size being truncated to is not a multiple of the
filesystem block size, because that would require decrypting the final
block, zeroing the part beyond i_size, then encrypting the block.

As other modifications to encrypted file contents are prohibited without
the key, just prohibit truncate(2) as well, making it fail with ENOKEY.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Acked-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index ac8b943817e609521bbc489c74e8b6513265ab59..61ee029d7e48e30a13bf38fac56028fd26b53e6a 100644 (file)
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -710,9 +710,13 @@ int f2fs_setattr(struct dentry *dentry, struct iattr *attr)
                return err;
 
        if (attr->ia_valid & ATTR_SIZE) {
-               if (f2fs_encrypted_inode(inode) &&
-                               fscrypt_get_encryption_info(inode))
-                       return -EACCES;
+               if (f2fs_encrypted_inode(inode)) {
+                       err = fscrypt_get_encryption_info(inode);
+                       if (err)
+                               return err;
+                       if (!fscrypt_has_encryption_key(inode))
+                               return -ENOKEY;
+               }
 
                if (attr->ia_size <= i_size_read(inode)) {
                        down_write(&F2FS_I(inode)->i_mmap_sem);