ext4: 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>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 754c2190af3148cd60f1d0a8006918ef3198937a..daed9b38362aab123942bf68c86c85c8de6fff6c 100644 (file)
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -5323,6 +5323,14 @@ int ext4_setattr(struct dentry *dentry, struct iattr *attr)
                loff_t oldsize = inode->i_size;
                int shrink = (attr->ia_size <= inode->i_size);
 
+               if (ext4_encrypted_inode(inode)) {
+                       error = fscrypt_get_encryption_info(inode);
+                       if (error)
+                               return error;
+                       if (!fscrypt_has_encryption_key(inode))
+                               return -ENOKEY;
+               }
+
                if (!(ext4_test_inode_flag(inode, EXT4_INODE_EXTENTS))) {
                        struct ext4_sb_info *sbi = EXT4_SB(inode->i_sb);