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Message-ID: <CAG48ez1NqoW8bByrYe30MdyCn2th3X+tth=VhMHA2MA-PoaQVw@mail.gmail.com>
Date: Wed, 26 Sep 2018 23:26:07 +0200
From: Jann Horn <jannh@...gle.com>
To: Casey Schaufler <casey.schaufler@...el.com>
Cc: Kernel Hardening <kernel-hardening@...ts.openwall.com>,
kernel list <linux-kernel@...r.kernel.org>,
linux-security-module <linux-security-module@...r.kernel.org>, selinux@...ho.nsa.gov,
Dave Hansen <dave.hansen@...el.com>, deneen.t.dock@...el.com, kristen@...ux.intel.com,
Arjan van de Ven <arjan@...ux.intel.com>
Subject: Re: [PATCH v5 4/5] Capability: Complete PTRACE_MODE_SCHED
On Wed, Sep 26, 2018 at 10:35 PM Casey Schaufler
<casey.schaufler@...el.com> wrote:
> Allow a complete ptrace access check with mode PTRACE_MODE_SCHED.
> Disable the inappropriate privilege check in the capability code
> that does incompatible locking.
What's that locking you're talking about?
> Signed-off-by: Casey Schaufler <casey.schaufler@...el.com>
> ---
> kernel/ptrace.c | 2 --
> security/commoncap.c | 2 ++
> 2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/ptrace.c b/kernel/ptrace.c
> index 99cfddde6a55..0b6a9df51c3b 100644
> --- a/kernel/ptrace.c
> +++ b/kernel/ptrace.c
> @@ -331,8 +331,6 @@ static int __ptrace_may_access(struct task_struct *task, unsigned int mode)
> !ptrace_has_cap(mm->user_ns, mode)))
> return -EPERM;
>
> - if (mode & PTRACE_MODE_SCHED)
> - return 0;
> return security_ptrace_access_check(task, mode);
> }
>
> diff --git a/security/commoncap.c b/security/commoncap.c
> index 2e489d6a3ac8..e77457110d05 100644
> --- a/security/commoncap.c
> +++ b/security/commoncap.c
> @@ -152,6 +152,8 @@ int cap_ptrace_access_check(struct task_struct *child, unsigned int mode)
> if (cred->user_ns == child_cred->user_ns &&
> cap_issubset(child_cred->cap_permitted, *caller_caps))
> goto out;
> + if (mode & PTRACE_MODE_SCHED)
> + goto out;
So for PTRACE_MODE_SCHED, this function always returns 0, right? If
that's intentional, perhaps you should instead just put "if (mode &
PTRACE_MODE_SCHED) return 0;" at the start of the function, to avoid
taking the RCU read lock in this case.
> if (ns_capable(child_cred->user_ns, CAP_SYS_PTRACE))
> goto out;
> ret = -EPERM;
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