On Fri, 2018-11-23 at 11:03 -0800, Casey Schaufler wrote: > On 11/22/2018 7:49 AM, Roberto Sassu wrote: > > Although rootfs (tmpfs) supports xattrs, they are not set due to the > > limitation of the cpio format. A new format called 'newcx' was proposed to > > overcome this limitation. > > > > However, it looks like that adding a new format is not simple: 15 kernel > > patches; user space tools must support the new format; mistakes made in the > > past should be avoided; it is unclear whether the kernel should switch from > > cpio to tar. > > > > The aim of this patch is to provide the same functionality without > > introducing a new format. The value of xattrs is placed in regular files > > having the same file name as the files xattrs are added to, plus a > > separator and the xattr name (<filename>.xattr-<xattr name>). > > > > Example: > > > > '/bin/cat.xattr-security.ima' is the name of a file containing the value of > > the security.ima xattr to be added to /bin/cat. > > > > At kernel initialization time, the kernel iterates over the rootfs > > filesystem, and if it encounters files with the '.xattr-' separator, it > > reads the content and adds the xattr to the file without the suffix. > > No. > > Really, no. > > It would be incredibly easy to use this mechanism to break > into systems. > > > > This proposal requires that LSMs and IMA allow the read and setxattr > > operations. This should not be a concern since: files with xattr values > > are not parsed by the kernel; user space processes are not yet executed. > > > > It would be possible to include all xattrs in the same file, but this > > increases the risk of the kernel being compromised by parsing the content. > > The kernel mustn't do this. Mustn't do what? Store the xattr as separate detached files, include all the xattrs in a single or per security/LSM xattr attribute file(s), or either? Mimi
