Messages in this thread | | | Date | Wed, 26 Jan 2022 15:41:45 +0800 | Subject | Re: [RESEND][PATCH] Documentation: added order requirement for ima_hash= | From | "Guozihua (Scott)" <> |
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On 2022/1/26 12:37, Mimi Zohar wrote: > On Wed, 2022-01-26 at 10:28 +0800, Guozihua (Scott) wrote: >> >> On 2022/1/26 9:07, Mimi Zohar wrote: >>> On Tue, 2022-01-25 at 17:02 +0800, GUO Zihua wrote: >>>> From: Guo Zihua <guozihua@huawei.com> >>>> >>>> Commandline parameter ima_hash= and ima_template= has order requirement >>>> for them to work correctly together. Namely ima_hash= must be >>>> specified after ima_template=, otherwise ima_template= will be ignored. >>>> >>>> The reason is that when handling ima_hash=, ima template would be set to >>>> the default value if it has not been initialized already, and that value >>>> cannot be changed afterwards by ima_template=. >>>> >>>> This patch adds this limitation to the documentation. >>>> >>>> Reviewed-by: Roberto Sassu <roberto.sassu@huawei.com> >>>> Signed-off-by: Guo Zihua <guozihua@huawei.com> >>> >>> This issue should be limited to the original "ima" template format, >>> which only supports hash algorithms of 20 bytes or less. The "ima_ng" >>> template has been the default since larger digests and templates were >>> upstreamed back in Linux 3.13[1]. Do you really still have kernels >>> built with the original "ima" template? >>> >>> [1] Refer to commit 4286587dccd4 ("ima: add Kconfig default measurement >>> list template"). >> >> Hi Mimi, >> >> The issue is that if ima_hash is specified before ima_template, >> ima_template will not work. Built-in default only affects which template >> will be loaded eventually. >> >> For example, if the built-in default template is ima-ng and user would >> like to change it to ima-sig with sha512 by specifying "ima_hash=sha512 >> ima_template=ima-sig" in command line, the result will be ima-ng with >> sha512, not ima-sig with sha512. > > Ok. Once the template name is set, ima_template_setup() doesn't allow > it to be reset. This was probably done to set the template name to the > first occurance of "ima_template=" on the boot command line. This > concern could be addressed by defining a static local variable in > ima_template_setup(). > > So either documenting the ordering requirement, as you've done, or > allowing the template_name to be reset are fine. > > thanks, > > Mimi > > .
The main issue lies in ima_template_desc_current called by hash_setup, which does not just read ima_template global variable, but also tries to set it if that hasn't been done already. Causing ima_template_setup to quit.
-- Best GUO Zihua
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