On 30/10/2020 16:47, Jann Horn wrote:
> On Fri, Oct 30, 2020 at 1:39 PM Mickaël Salaün <m...@digikod.net> wrote:
>> Commit 69f594a38967 ("ptrace: do not audit capability check when outputing
>> /proc/pid/stat") replaced the use of ns_capable() with
>> has_ns_capability{,_noaudit}() which doesn't set PF_SUPERPRIV.
>>
>> Commit 6b3ad6649a4c ("ptrace: reintroduce usage of subjective credentials in
>> ptrace_has_cap()") replaced has_ns_capability{,_noaudit}() with
>> security_capable(), which doesn't set PF_SUPERPRIV neither.
>>
>> Since commit 98f368e9e263 ("kernel: Add noaudit variant of ns_capable()"), a
>> new ns_capable_noaudit() helper is available. Let's use it!
>>
>> As a result, the signature of ptrace_has_cap() is restored to its original
>> one.
>>
>> Cc: Christian Brauner <christian.brau...@ubuntu.com>
>> Cc: Eric Paris <epa...@redhat.com>
>> Cc: Jann Horn <ja...@google.com>
>> Cc: Kees Cook <keesc...@chromium.org>
>> Cc: Oleg Nesterov <o...@redhat.com>
>> Cc: Serge E. Hallyn <se...@hallyn.com>
>> Cc: Tyler Hicks <tyhi...@linux.microsoft.com>
>> Cc: sta...@vger.kernel.org
>> Fixes: 6b3ad6649a4c ("ptrace: reintroduce usage of subjective credentials in
>> ptrace_has_cap()")
>> Fixes: 69f594a38967 ("ptrace: do not audit capability check when outputing
>> /proc/pid/stat")
>> Signed-off-by: Mickaël Salaün <m...@linux.microsoft.com>
>
> Yeah... I guess this makes sense. (We'd have to undo or change it if
> we ever end up needing to use a different set of credentials, e.g.
> from ->f_cred, but I guess that's really something we should avoid
> anyway.)
>
> Reviewed-by: Jann Horn <ja...@google.com>
>
> with one nit:
>
>
> [...]
>> /* Returns 0 on success, -errno on denial. */
>> static int __ptrace_may_access(struct task_struct *task, unsigned int mode)
>> {
>> - const struct cred *cred = current_cred(), *tcred;
>> + const struct cred *const cred = current_cred(), *tcred;
>
> This is an unrelated change, and almost no kernel code marks local
> pointer variables as "const". I would drop this change from the patch.
This give guarantee that the cred variable will not be used for
something else than current_cred(), which kinda prove that this patch
doesn't change the behavior of __ptrace_may_access() by not using cred
in ptrace_has_cap(). It doesn't hurt and I think it could be useful to
spot issues when backporting.
>
>> struct mm_struct *mm;
>> kuid_t caller_uid;
>> kgid_t caller_gid;
