On 4/27/2011 5:34 AM, Roberto Sassu wrote: > File descriptor labeling issue > > Actually SELinux and SMACK assign to file descriptors the same label of the > opening process and use it in LSM hooks security_file_permission(), > security_file_fcntl() and others to verify if the 'current' process has the > rights to perform the requested operation. > > Using the credentials of the 'current' process may be not appropriate in > case a file descriptor is opened by a kernel service (i.e. a filesystem) > and made shared among user processes. For instance, in a system with > SELinux and eCryptfs, if the process A opens an encrypted file, eCryptfs > obtains a file descriptor to access the correspondent inode in the lower > filesystem, labeled with the A's label. > > If the process B accesses the same encrypted file, it needs the 'use' > permission on the A's label other than permissions for the lower inode. > However, if B is the first accessing process, A needs the 'use' permission > on the B's label. I am having trouble understanding the argument. I will pose my question in Smack terms, as I can speak most definitively in them. A process running with a Smack label "A" creates a file, and that file gets labeled "A", as it ought. If eCryptfs is behaving correctly this ought not change. If eCryptfs in encrypting the label it needs to do so in such a way as to be able to decrypt it prior to presentation to the vfs layer, where it will be used in an access check. When the process running with a Smack label "B" comes along the vfs code will check the fetched and possibly decrypted "A" against "B" and, unless there is an explicit Smack rule in place granting "B" access to "A", fail. What is the problem? What is eCryptfs doing that prevents this from working? -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
