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    SubjectRe: [PATCH v9 23/23] ima: Enable IMA namespaces
    On Tue, Jan 25, 2022 at 05:46:45PM -0500, Stefan Berger wrote:
    > From: Stefan Berger <stefanb@linux.ibm.com>
    >
    > Introduce the IMA_NS in Kconfig for IMA namespace enablement.
    >
    > Enable the lazy initialization of an IMA namespace when a user mounts
    > SecurityFS and writes '1' into IMA's 'active' securityfs file. A
    > user_namespace will now get a pointer to an ima_namespace and therefore
    > implement get_current_ns() for the namespacing case that returns this
    > pointer. Use get_current_ns() in those places that require access to the
    > current IMA namespace. In some places, primarily those related to
    > IMA-appraisal and changes to file attributes, keep the pointer to
    > init_ima_ns, since there flags related to file measurements may be
    > affected, which are not supported in IMA namespaces, yet.
    >
    > Before using the ima_namespace pointer test it with ns_is_active()
    > to check whether it is NULL and whether the ima_namespace is active.
    > If it's not active, it cannot be used, yet. Therefore, return early
    > from those functions that may now get either get a NULL pointer from
    > this call or where ns->active is still 0. The init_ima_ns is always
    > set to be active, thus passing the check.
    >
    > Implement ima_ns_from_file() for SecurityFS-related files where we can
    > now get the IMA namespace via the user namespace pointer associated
    > with the superblock of the SecurityFS filesystem instance.
    >
    > Return -EACCES to IMA's securityfs files, except for the 'active' file,
    > until the IMA namespace has been set to active.
    >
    > Switch access to userns->ima_ns to use acquire/release semantics to ensure
    > that a newly created ima_namespace structure is fully visible upon access.
    >
    > Only emit the kernel log message 'policy update completed' for the
    > init_ima_ns.
    >
    > Gate access to ima_appraise variable to init_ima_ns in ima_load_data().
    >
    > Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
    >
    > ---
    > v9:
    > - ima_post_key_create_or_update: Only handle key if in init_ima_ns
    > - Removed ns == NULL checks where user_namespace is now passed
    > - Defer setting of user_ns->ima_ns until end of ima_fs_ns_init();
    > required new ima_free_imans() and new user_ns_set_ima_ns()
    > - Only emit log message 'policy update completed' for init_ima_ns
    > - Introduce get_current_ns() only in this patch
    > - Check for ns == &init_ima_ns in ima_load_data()
    > ---
    > include/linux/ima.h | 13 ++++
    > init/Kconfig | 13 ++++
    > kernel/user_namespace.c | 2 +
    > security/integrity/ima/ima.h | 51 ++++++++++++--
    > security/integrity/ima/ima_appraise.c | 3 +
    > security/integrity/ima/ima_asymmetric_keys.c | 6 +-
    > security/integrity/ima/ima_fs.c | 74 ++++++++++++++++----
    > security/integrity/ima/ima_init_ima_ns.c | 2 +
    > security/integrity/ima/ima_main.c | 35 +++++----
    > security/integrity/ima/ima_ns.c | 15 ++--
    > security/integrity/ima/ima_policy.c | 16 +++--
    > 11 files changed, 188 insertions(+), 42 deletions(-)
    >
    > diff --git a/include/linux/ima.h b/include/linux/ima.h
    > index c584527c0f47..4e595bd9733e 100644
    > --- a/include/linux/ima.h
    > +++ b/include/linux/ima.h
    > @@ -11,6 +11,7 @@
    > #include <linux/fs.h>
    > #include <linux/security.h>
    > #include <linux/kexec.h>
    > +#include <linux/user_namespace.h>
    > #include <crypto/hash_info.h>
    > struct linux_binprm;
    >
    > @@ -68,6 +69,18 @@ static inline const char * const *arch_get_ima_policy(void)
    > }
    > #endif
    >
    > +static inline struct user_namespace
    > +*ima_ns_to_user_ns(struct ima_namespace *ns)
    > +{
    > + struct user_namespace *user_ns;
    > +
    > + user_ns = current_user_ns();
    > +#ifdef CONFIG_IMA_NS
    > + WARN_ON(user_ns->ima_ns != ns);
    > +#endif
    > + return user_ns;
    > +}

    As I showed in [1] there are legitimate instances where ima_parse_rule()
    is reached and ima->user_ns != current_user_ns(). I illustrated two
    examples. So you should skip the current_user_ns() check in there.

    You should be able to trigger a WARN() expanding and fixing-up the
    pseudo-code of the second example in [1]. You should probably add a
    test-case for this if you have test-suite already.

    [1]: https://lore.kernel.org/lkml/20220114144515.vbler7ae3jqebhec@wittgenstein

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