On 30/10/2020 16:47, Jann Horn wrote:
On Fri, Oct 30, 2020 at 1:39 PM Mickaël Salaün mic@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.brauner@ubuntu.com Cc: Eric Paris eparis@redhat.com Cc: Jann Horn jannh@google.com Cc: Kees Cook keescook@chromium.org Cc: Oleg Nesterov oleg@redhat.com Cc: Serge E. Hallyn serge@hallyn.com Cc: Tyler Hicks tyhicks@linux.microsoft.com Cc: stable@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 mic@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 jannh@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;