On 12/27/2023 11:52 AM, Mimi Zohar wrote: > On Tue, 2023-12-26 at 12:14 -0800, Casey Schaufler wrote: >> On 12/26/2023 10:14 AM, Mimi Zohar wrote: >>> On Thu, 2023-12-14 at 18:08 +0100, Roberto Sassu wrote: >>>> From: Roberto Sassu <roberto.sassu@xxxxxxxxxx> >>>> >>>> Move hardcoded IMA function calls (not appraisal-specific functions) from >>>> various places in the kernel to the LSM infrastructure, by introducing a >>>> new LSM named 'ima' (at the end of the LSM list and always enabled like >>>> 'integrity'). >>>> >>>> Having IMA before EVM in the Makefile is sufficient to preserve the >>>> relative order of the new 'ima' LSM in respect to the upcoming 'evm' LSM, >>>> and thus the order of IMA and EVM function calls as when they were >>>> hardcoded. >>>> >>>> Make moved functions as static (except ima_post_key_create_or_update(), >>>> which is not in ima_main.c), and register them as implementation of the >>>> respective hooks in the new function init_ima_lsm(). >>>> >>>> A slight difference is that IMA and EVM functions registered for the >>>> inode_post_setattr, inode_post_removexattr, path_post_mknod, >>>> inode_post_create_tmpfile, inode_post_set_acl and inode_post_remove_acl >>>> won't be executed for private inodes. Since those inodes are supposed to be >>>> fs-internal, they should not be of interest of IMA or EVM. The S_PRIVATE >>>> flag is used for anonymous inodes, hugetlbfs, reiserfs xattrs, XFS scrub >>>> and kernel-internal tmpfs files. >>>> >>>> Conditionally register ima_post_path_mknod() if CONFIG_SECURITY_PATH is >>>> enabled, otherwise the path_post_mknod hook won't be available. >>> Up to this point, enabling CONFIG_SECURITY_PATH was not required. By >>> making it conditional on CONFIG_SECURITY_PATH, anyone enabling IMA will >>> also need to enable CONFIG_SECURITY_PATH. Without it, new files will >>> not be tagged as a "new" file. >>> >>> Casey, Paul, how common is it today not to enable CONFIG_SECURITY_PATH? >>> Will enabling it just for IMA be a problem? >> Landlock, AppArmor and TOMOYO require it. Fedora enables Landlock and Ubuntu >> enables AppArmor. I expect that, except for "minimal" distributions, you >> won't get any push back. If a distribution is striving for minimal, it's not >> going to use IMA. >> >> It makes me wonder if eliminating CONFIG_SECURITY_PATH might not be a >> rational alternative. > Embedded systems were the first to use IMA for file signature > verification, not distros. Could they have enabled > SELinux, lockdown, and IMA? Yes, they could have. I know some have used Smack and some SELinux. That's not really relevant, as neither of those use path hooks. My thought is that CONFIG_SECURITY_PATH adds more aggravation than value, but I can't quote numbers on either. I don't see a problem with IMA using path hooks. I also wouldn't see harm in moving the hook(s) you need for IMA out from that configuration option and into the general set. With the current rate of new hook additions I can't see moving an existing hook as a problem.
