linux-kernel - Re: [PATCH V3] security/selinux: Always allow FIOCLEX and FIONCLEX

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Message-ID: <CAHC9VhT4V=d8LtNT2mbiB6m1eUypi5WxPdRux_YNJ9iCV=WjWg@mail.gmail.com>
Date:   Thu, 24 Feb 2022 19:34:20 -0500
From:   Paul Moore <paul@...l-moore.com>
To:     Richard Haines <richard_c_haines@...nternet.com>,
        selinux@...r.kernel.org
Cc:     stephen.smalley.work@...il.com, eparis@...isplace.org,
        demiobenour@...il.com, linux-kernel@...r.kernel.org,
        selinux-refpolicy@...r.kernel.org, jeffv@...gle.com
Subject: Re: [PATCH V3] security/selinux: Always allow FIOCLEX and FIONCLEX

On Thu, Feb 24, 2022 at 5:24 AM Richard Haines
<richard_c_haines@...nternet.com> wrote:
>
> These ioctls are equivalent to fcntl(fd, F_SETFD, flags), which SELinux
> always allows too.  Furthermore, a failed FIOCLEX could result in a file
> descriptor being leaked to a process that should not have access to it.
>
> As this patch removes access controls, a policy capability needs to be
> enabled in policy to always allow these ioctls.
>
> Based-on-patch-by: Demi Marie Obenour <demiobenour@...il.com>
> Signed-off-by: Richard Haines <richard_c_haines@...nternet.com>
> ---
> V2 Change: Control via a policy capability.
> V3 Change: Update switch check.
>
>  security/selinux/hooks.c                   | 6 ++++++
>  security/selinux/include/policycap.h       | 1 +
>  security/selinux/include/policycap_names.h | 3 ++-
>  security/selinux/include/security.h        | 7 +++++++
>  4 files changed, 16 insertions(+), 1 deletion(-)

This looks good to me, but before I merge this are the SELinux
userspace folks okay with the policy capability's name and enum value?

> diff --git a/security/selinux/hooks.c b/security/selinux/hooks.c
> index 5b6895e4f..d369c2d82 100644
> --- a/security/selinux/hooks.c
> +++ b/security/selinux/hooks.c
> @@ -3745,6 +3745,12 @@ static int selinux_file_ioctl(struct file *file, unsigned int cmd,
>                                             CAP_OPT_NONE, true);
>                 break;
>
> +       case FIOCLEX:
> +       case FIONCLEX:
> +               if (!selinux_policycap_ioctl_skip_cloexec())
> +                       error = ioctl_has_perm(cred, file, FILE__IOCTL, (u16) cmd);
> +               break;
> +
>         /* default case assumes that the command will go
>          * to the file's ioctl() function.
>          */
> diff --git a/security/selinux/include/policycap.h b/security/selinux/include/policycap.h
> index 2ec038efb..44d73dc32 100644
> --- a/security/selinux/include/policycap.h
> +++ b/security/selinux/include/policycap.h
> @@ -11,6 +11,7 @@ enum {
>         POLICYDB_CAPABILITY_CGROUPSECLABEL,
>         POLICYDB_CAPABILITY_NNP_NOSUID_TRANSITION,
>         POLICYDB_CAPABILITY_GENFS_SECLABEL_SYMLINKS,
> +       POLICYDB_CAPABILITY_IOCTL_CLOEXEC,
>         __POLICYDB_CAPABILITY_MAX
>  };
>  #define POLICYDB_CAPABILITY_MAX (__POLICYDB_CAPABILITY_MAX - 1)
> diff --git a/security/selinux/include/policycap_names.h b/security/selinux/include/policycap_names.h
> index b89289f09..ebd64afe1 100644
> --- a/security/selinux/include/policycap_names.h
> +++ b/security/selinux/include/policycap_names.h
> @@ -12,7 +12,8 @@ const char *selinux_policycap_names[__POLICYDB_CAPABILITY_MAX] = {
>         "always_check_network",
>         "cgroup_seclabel",
>         "nnp_nosuid_transition",
> -       "genfs_seclabel_symlinks"
> +       "genfs_seclabel_symlinks",
> +       "ioctl_skip_cloexec"
>  };
>
>  #endif /* _SELINUX_POLICYCAP_NAMES_H_ */
> diff --git a/security/selinux/include/security.h b/security/selinux/include/security.h
> index ac0ece013..8a789c22b 100644
> --- a/security/selinux/include/security.h
> +++ b/security/selinux/include/security.h
> @@ -219,6 +219,13 @@ static inline bool selinux_policycap_genfs_seclabel_symlinks(void)
>         return READ_ONCE(state->policycap[POLICYDB_CAPABILITY_GENFS_SECLABEL_SYMLINKS]);
>  }
>
> +static inline bool selinux_policycap_ioctl_skip_cloexec(void)
> +{
> +       struct selinux_state *state = &selinux_state;
> +
> +       return READ_ONCE(state->policycap[POLICYDB_CAPABILITY_IOCTL_CLOEXEC]);
> +}
> +
>  struct selinux_policy_convert_data;
>
>  struct selinux_load_state {
> --
> 2.35.1

-- 
paul-moore.com