On 19-10, Mimi Zohar wrote: > On Wed, 2017-10-18 at 17:49 -0200, Bruno E. O. Meneguele wrote: > > On 14-10, Mimi Zohar wrote: > > > On Thu, 2017-10-12 at 10:55 -0400, Bruno E. O. Meneguele wrote: > > > > Hi, > > > > > > > > recently, while playing around with IMA modules check support, I notice > > > > that when the kernel was compiled/installed with XZ-compressed modules > > > > the IMA kernel infra returns -EACCESS on modules initialization. Let me > > > > detail a bit more: > > > > > > > > I created the policy file (/etc/ima/ima-policy) with > > > > > > > > measure func=MODULE_CHECK uid=0 > > > > (... and more, policy file is attached) > > > > > > > > then rebooted the kernel (that was built with XZ-compressed modules) and > > > > a bunch of modules didn't load, e.g.: > > > > > > > > without ima-policy: > > > > # lsmod | wc -l > > > > 32 > > > > > > > > with it: > > > > # lsmod | wc -l > > > > 14 > > > > > > > > these 14 modules were all loaded during initram booting phase, but if I > > > > rmmod some of them and try to modprobe (strace output): > > > > > > > > init_module(0x55b9bcc9bba0, 17763, "") = -1 EACCES (Permission denied) > > > > > > > > The point is that there is no violation, because the error occurs right > > > > after kmod calls init_module() and the call follows to ima_read_file() > > > > (kernel tree: security/integrity/ima/ima_main.c) which returns -EACCES, > > > > since there is no 'file' structure available (init_module uses memory > > > > region only and not file descriptor). > > > > > > IMA hashes/signatures are stored as xattrs, which requires a file > > > descriptor. IMA only supports the new kernel module syscall, which > > > provides the file descriptor. > > > > > > > Patches from Thiago Bauerman > > (http://www.spinics.net/lists/linux-integrity/msg00243.html) could help > > to solve this, don't they? > > True. Initially we're introducing appended signature support for > kernel images. Afterwards, perhaps we'll be able to use it to close > other appraisal gaps (e.g bpf). > Ah right, nice. I'll keep an eye on it. > > > > I notice this behavior using Fedora 26 (using SELinux as sec framework) > > > > and up-to-date kernel, the question is: should IMA kernel mechanism > > > > support memory regions integrity measurements, maybe following the steps > > > > that MODULE_SIGNATURE takes (that check for module signature through its > > > > mmap region), allowing compressed modules to be loaded? Or kernels built > > > > with XZ/GZ-compressed modules was never meant to be supported? Is it a > > > > bug or a possible enhancement? > > > > > > If the IMA policy requires kernel modules to be signed, an appended > > > signature is permitted as long as the kernel is configured with > > > CONFIG_MODULE_SIG_FORCE enabled. > > > > > > > Right, but it's also possible to note that CONFIG_MODULE_SIG_FORCE is > > handled on kernel/module.c and has a kernel cmdline param, > > module.sig_enforce, that is read in case CONFIG_MODULE_SIG_FORCE is not > > set. Wouldn't be better ima_read_file depend on this cmdline param > > instead directly on the CONFIG? That way kernels compiled without > > CONFIG_MODULE_SIG_FORCE set as default would have the option to enable > > the kernel param and use their normal policy (MODULE_CHECK). > > > > What do you think? > > I wasn't aware of the module_param. Thank you for pointing it out. > "sig_enforce" is currently defined as static. Should it be defined > as __initdata? > Well, at first I thought it could stay as it is and just create a "getter" function, like "is_module_sig_enforced()", and use it on ima_main.c through module.h, since this code would be called to every module loaded in runtime. If it's ok to you I can try to write a patch against integrity-next and see how it behaves. -- bmeneg PGP Key: http://bmeneg.com/pubkey.txt
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