On Thu, 2022-09-29 at 21:44 -0400, Mimi Zohar wrote: > Hi Christian, > > On Thu, 2022-09-29 at 17:30 +0200, Christian Brauner wrote: > > The security_inode_post_setxattr() hook is used by security modules to > > update their own security.* xattrs. Consequently none of the security > > modules operate on posix acls. So we don't need an additional security > > hook when post setting posix acls. > > > > However, the integrity subsystem wants to be informed about posix acl > > changes and specifically evm to update their hashes when the xattrs > > change. > > ^... to be informed about posix acl changes in order to reset the EVM > status flag. > > > The callchain for evm_inode_post_setxattr() is: > > > > -> evm_inode_post_setxattr() > > Resets the EVM status flag for both EVM signatures and HMAC. > > > -> evm_update_evmxattr() > > evm_update_evmxattr() is only called for "security.evm", not acls. > > > -> evm_calc_hmac() > > -> evm_calc_hmac_or_hash() > > > > and evm_cacl_hmac_or_hash() walks the global list of protected xattr > > names evm_config_xattrnames. This global list can be modified via > > /sys/security/integrity/evm/evm_xattrs. The write to "evm_xattrs" is > > restricted to security.* xattrs and the default xattrs in > > evm_config_xattrnames only contains security.* xattrs as well. > > > > So the actual value for posix acls is currently completely irrelevant > > for evm during evm_inode_post_setxattr() and frankly it should stay that > > way in the future to not cause the vfs any more headaches. But if the > > actual posix acl values matter then evm shouldn't operate on the binary > > void blob and try to hack around in the uapi struct anyway. Instead it > > should then in the future add a dedicated hook which takes a struct > > posix_acl argument passing the posix acls in the proper vfs format. > > > > For now it is sufficient to make evm_inode_post_set_acl() a wrapper > > around evm_inode_post_setxattr() not passing any actual values down. > > This will still cause the hashes to be updated as before. > > ^This will cause the EVM status flag to be reset. Sorry, please ignore these comments for the moment.
