* [PATCH] security: Use user_namespace::level to avoid redundant iterations in cap_capable()
@ 2017-05-02 12:40 Kirill Tkhai
2017-05-02 16:36 ` Andy Lutomirski
0 siblings, 1 reply; 2+ messages in thread
From: Kirill Tkhai @ 2017-05-02 12:40 UTC (permalink / raw)
To: serge, ebiederm, agruenba, gregkh, linux-kernel, oleg, paul,
ktkhai, viro, avagin, linux-api, linux-fsdevel, mtk.manpages,
akpm, luto, gorcunov, mingo, keescook
When ns->level is not larger then cred->user_ns->level,
then ns can't be cred->user_ns's descendant, and
there is no a sence to search in parents.
So, breake the cycle earlier and skip needless iterations.
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
---
security/commoncap.c | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)
diff --git a/security/commoncap.c b/security/commoncap.c
index 78b37838a2d3..f6ef78208d2d 100644
--- a/security/commoncap.c
+++ b/security/commoncap.c
@@ -82,8 +82,11 @@ int cap_capable(const struct cred *cred, struct user_namespace *targ_ns,
if (ns == cred->user_ns)
return cap_raised(cred->cap_effective, cap) ? 0 : -EPERM;
- /* Have we tried all of the parent namespaces? */
- if (ns == &init_user_ns)
+ /*
+ * If ns can't be a descendant of cred->user_ns, then it's
+ * needlessly to go up.
+ */
+ if (ns->level <= cred->user_ns->level)
return -EPERM;
/*
^ permalink raw reply related [flat|nested] 2+ messages in thread
* Re: [PATCH] security: Use user_namespace::level to avoid redundant iterations in cap_capable()
2017-05-02 12:40 [PATCH] security: Use user_namespace::level to avoid redundant iterations in cap_capable() Kirill Tkhai
@ 2017-05-02 16:36 ` Andy Lutomirski
0 siblings, 0 replies; 2+ messages in thread
From: Andy Lutomirski @ 2017-05-02 16:36 UTC (permalink / raw)
To: Kirill Tkhai
Cc: Serge E. Hallyn, Eric W. Biederman, Andreas Gruenbacher, Greg KH,
linux-kernel, Oleg Nesterov, Paul Moore, Al Viro, Andrey Vagin,
Linux API, Linux FS Devel, Michael Kerrisk, Andrew Morton,
Cyrill Gorcunov, Ingo Molnar, Kees Cook
On Tue, May 2, 2017 at 5:40 AM, Kirill Tkhai <ktkhai@virtuozzo.com> wrote:
> When ns->level is not larger then cred->user_ns->level,
> then ns can't be cred->user_ns's descendant, and
> there is no a sence to search in parents.
>
> So, breake the cycle earlier and skip needless iterations.
>
> Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
> ---
> security/commoncap.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/security/commoncap.c b/security/commoncap.c
> index 78b37838a2d3..f6ef78208d2d 100644
> --- a/security/commoncap.c
> +++ b/security/commoncap.c
> @@ -82,8 +82,11 @@ int cap_capable(const struct cred *cred, struct user_namespace *targ_ns,
> if (ns == cred->user_ns)
> return cap_raised(cred->cap_effective, cap) ? 0 : -EPERM;
>
> - /* Have we tried all of the parent namespaces? */
> - if (ns == &init_user_ns)
> + /*
> + * If ns can't be a descendant of cred->user_ns, then it's
> + * needlessly to go up.
> + */
> + if (ns->level <= cred->user_ns->level)
> return -EPERM;
This is a nice improvement, but the comment could be better. How
about "If we're already at a lower level than we're looking for, we're
done searching."
--Andy
^ permalink raw reply [flat|nested] 2+ messages in thread
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