On Wed, 2022-04-06 at 14:16 +0800, GUO Zihua wrote:
> It is discovered thatO allowing template "ima" as the compiled default
> would cause the following issue: the boot command line option
> "ima_hash=" must be behind "ima_template=", otherwise "ima_hash=" might
> be rejected.
The format of a proper patch description describes the current status,
provides a succinct problem description, followed by the solution.
The original 'ima' measurement list template contains a hash, defined
as 20 bytes, and a null terminated pathname, limited to 255
characters. Other measurement list templates permit both larger hashes
and longer pathnames. When the "ima" template is configured as the
default, a new measurement list template (ima_template=) must be
specified before specifying a larger hash algorithm (ima_hash=) on the
boot command line.
To avoid this boot command line ordering issue, remove the legacy "ima"
template configuration option, allowing it to still be specified on the
boot command line.
>
> The root cause of this issue is that during the processing of ima_hash,
> we would try to check whether the hash algorithm is compatible with the
> template. If the template is not set at the moment we do the check, we
> check the algorithm against the compiled default template. If the
> complied default template is "ima", then we reject any hash algorithm
> other than sha1 and md5.
>
> For example, if the compiled default template is "ima", and the default
> algorithm is sha1 (which is the current default). In the cmdline, we put
> in "ima_hash=sha256 ima_template=ima-ng". The expected behavior would be
> that ima starts with ima-ng as the template and sha256 as the hash
> algorithm. However, during the processing of "ima_hash=",
> "ima_template=" has not been processed yet, and hash_setup would check
> the configured hash algorithm against the compiled default: ima, and
> reject sha256. So at the end, the hash algorithm that is actually used
> will be sha1.
>
> With template "ima" removed from the compiled default, we ensure that
> the default tempalte would at least be "ima-ng" which allows for
> basically any hash algorithm. Users who needs to use "ima" template
> could still do it by specifying "ima_template=ima" in boot command line.
>
> This change would not break the algorithm compatibility checking for
> IMA.
>
> Fixes: 4286587dccd43 ("ima: add Kconfig default measurement list template")
> Signed-off-by: GUO Zihua <guozihua@xxxxxxxxxx>
> ---
> security/integrity/ima/Kconfig | 22 +++++++++-------------
> 1 file changed, 9 insertions(+), 13 deletions(-)
>
> diff --git a/security/integrity/ima/Kconfig b/security/integrity/ima/Kconfig
> index f3a9cc201c8c..f392cac7a7d1 100644
> --- a/security/integrity/ima/Kconfig
> +++ b/security/integrity/ima/Kconfig
> @@ -65,14 +65,11 @@ choice
> help
> Select the default IMA measurement template.
>
> - The original 'ima' measurement list template contains a
> - hash, defined as 20 bytes, and a null terminated pathname,
> - limited to 255 characters. The 'ima-ng' measurement list
> - template permits both larger hash digests and longer
> - pathnames.
> -
> - config IMA_TEMPLATE
> - bool "ima"
> + The 'ima-ng' measurement list template permits various hash
> + digests and long pathnames. The compiled default template
> + can be overwritten using the kernel command line
> + 'ima_template=' option.
> +
Other than perhaps changing "contains" to "contained", there's no
reason for changing the text. Adding an additional line is fine - The
configured default template can be replaced by specifying
"ima_template=" on the boot command line.
> config IMA_NG_TEMPLATE
> bool "ima-ng (default)"
> config IMA_SIG_TEMPLATE
> @@ -82,7 +79,6 @@ endchoice
> config IMA_DEFAULT_TEMPLATE
> string
> depends on IMA
> - default "ima" if IMA_TEMPLATE
> default "ima-ng" if IMA_NG_TEMPLATE
> default "ima-sig" if IMA_SIG_TEMPLATE
>
> @@ -102,19 +98,19 @@ choice
>
> config IMA_DEFAULT_HASH_SHA256
> bool "SHA256"
> - depends on CRYPTO_SHA256=y && !IMA_TEMPLATE
> + depends on CRYPTO_SHA256=y
>
> config IMA_DEFAULT_HASH_SHA512
> bool "SHA512"
> - depends on CRYPTO_SHA512=y && !IMA_TEMPLATE
> + depends on CRYPTO_SHA512=y
>
> config IMA_DEFAULT_HASH_WP512
> bool "WP512"
> - depends on CRYPTO_WP512=y && !IMA_TEMPLATE
> + depends on CRYPTO_WP512=y
>
> config IMA_DEFAULT_HASH_SM3
> bool "SM3"
> - depends on CRYPTO_SM3=y && !IMA_TEMPLATE
> + depends on CRYPTO_SM3=y
> endchoice
>
> config IMA_DEFAULT_HASH
