linux-kernel - Re: [PATCH 6/5] capability: Repair sidechannel test in ptrace

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Message-ID: <CAG48ez1qZQqffLfB_JV=UB12QjFWmfHm2=PH2eiF+Z_yn9RhpA@mail.gmail.com>
Date:   Thu, 27 Sep 2018 21:49:10 +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 6/5] capability: Repair sidechannel test in ptrace

On Thu, Sep 27, 2018 at 9:17 PM Casey Schaufler
<casey.schaufler@...el.com> wrote:
>
> From: Casey Schaufler <casey@...aufler-ca.com>
>
> The PTRACE_MODE_SCHED check erroniously returns 0 in
> all cases. It should be returning -EPERM. This fixes
> the logic to correct that error.
>
> Signed-off-by: Casey Schaufler <casey.schaufler@...el.com>

Reviewed-by: Jann Horn <jannh@...gle.com>

> ---
>  security/commoncap.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/security/commoncap.c b/security/commoncap.c
> index e77457110d05..70a7e3d19c16 100644
> --- a/security/commoncap.c
> +++ b/security/commoncap.c
> @@ -152,9 +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;
> -       if (ns_capable(child_cred->user_ns, CAP_SYS_PTRACE))
> +       if (!(mode & PTRACE_MODE_SCHED) &&
> +           ns_capable(child_cred->user_ns, CAP_SYS_PTRACE))
>                 goto out;
>         ret = -EPERM;
>  out:
> --
> 2.17.1
>