From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.7 required=3.0 tests=DKIM_ADSP_CUSTOM_MED, FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1A264C43331 for ; Sat, 28 Mar 2020 21:24:00 +0000 (UTC) Received: from mother.openwall.net (mother.openwall.net [195.42.179.200]) by mail.kernel.org (Postfix) with SMTP id 7511D20857 for ; Sat, 28 Mar 2020 21:23:59 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 7511D20857 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kernel-hardening-return-18270-kernel-hardening=archiver.kernel.org@lists.openwall.com Received: (qmail 28303 invoked by uid 550); 28 Mar 2020 21:23:54 -0000 Mailing-List: contact kernel-hardening-help@lists.openwall.com; run by ezmlm Precedence: bulk List-Post: List-Help: List-Unsubscribe: List-Subscribe: List-ID: Received: (qmail 28283 invoked from network); 28 Mar 2020 21:23:53 -0000 Date: Sat, 28 Mar 2020 22:23:36 +0100 From: Alexey Gladkov To: Kees Cook Cc: LKML , Kernel Hardening , Linux API , Linux FS Devel , Linux Security Module , Akinobu Mita , Alexander Viro , Alexey Dobriyan , Andrew Morton , Andy Lutomirski , Daniel Micay , Djalal Harouni , "Dmitry V . Levin" , "Eric W . Biederman" , Greg Kroah-Hartman , Ingo Molnar , "J . Bruce Fields" , Jeff Layton , Jonathan Corbet , Linus Torvalds , Oleg Nesterov Subject: Re: [PATCH v10 4/9] proc: instantiate only pids that we can ptrace on 'hidepid=4' mount option Message-ID: <20200328212336.zyj5naxz4jc64tgp@comp-core-i7-2640m-0182e6> References: <20200327172331.418878-1-gladkov.alexey@gmail.com> <20200327172331.418878-5-gladkov.alexey@gmail.com> <202003281336.8354DB74@keescook> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <202003281336.8354DB74@keescook> X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.6.1 (raptor.unsafe.ru [5.9.43.93]); Sat, 28 Mar 2020 21:23:42 +0000 (UTC) On Sat, Mar 28, 2020 at 01:40:03PM -0700, Kees Cook wrote: > On Fri, Mar 27, 2020 at 06:23:26PM +0100, Alexey Gladkov wrote: > > If "hidepid=4" mount option is set then do not instantiate pids that > > we can not ptrace. "hidepid=4" means that procfs should only contain > > pids that the caller can ptrace. > > > > Cc: Kees Cook > > Cc: Andy Lutomirski > > Signed-off-by: Djalal Harouni > > Reviewed-by: Alexey Dobriyan > > Signed-off-by: Alexey Gladkov > > --- > > fs/proc/base.c | 15 +++++++++++++++ > > fs/proc/root.c | 13 ++++++++++--- > > include/linux/proc_fs.h | 1 + > > 3 files changed, 26 insertions(+), 3 deletions(-) > > > > diff --git a/fs/proc/base.c b/fs/proc/base.c > > index 43a28907baf9..1ebe9eba48ea 100644 > > --- a/fs/proc/base.c > > +++ b/fs/proc/base.c > > @@ -701,6 +701,14 @@ static bool has_pid_permissions(struct proc_fs_info *fs_info, > > struct task_struct *task, > > int hide_pid_min) > > { > > + /* > > + * If 'hidpid' mount option is set force a ptrace check, > > + * we indicate that we are using a filesystem syscall > > + * by passing PTRACE_MODE_READ_FSCREDS > > + */ > > + if (fs_info->hide_pid == HIDEPID_NOT_PTRACEABLE) > > + return ptrace_may_access(task, PTRACE_MODE_READ_FSCREDS); > > + > > if (fs_info->hide_pid < hide_pid_min) > > return true; > > if (in_group_p(fs_info->pid_gid)) > > @@ -3319,7 +3327,14 @@ struct dentry *proc_pid_lookup(struct dentry *dentry, unsigned int flags) > > if (!task) > > goto out; > > > > + /* Limit procfs to only ptraceable tasks */ > > + if (fs_info->hide_pid == HIDEPID_NOT_PTRACEABLE) { > > + if (!has_pid_permissions(fs_info, task, HIDEPID_NO_ACCESS)) > > + goto out_put_task; > > + } > > + > > result = proc_pid_instantiate(dentry, task, NULL); > > +out_put_task: > > put_task_struct(task); > > out: > > return result; > > diff --git a/fs/proc/root.c b/fs/proc/root.c > > index 616e8976185c..62eae22403d2 100644 > > --- a/fs/proc/root.c > > +++ b/fs/proc/root.c > > @@ -47,6 +47,14 @@ static const struct fs_parameter_spec proc_fs_parameters[] = { > > {} > > }; > > > > +static inline int valid_hidepid(unsigned int value) > > +{ > > + return (value == HIDEPID_OFF || > > + value == HIDEPID_NO_ACCESS || > > + value == HIDEPID_INVISIBLE || > > + value == HIDEPID_NOT_PTRACEABLE); > > This likely easier to do with a ...MAX value? i.e. > > return (value < HIDEPID_OFF || value >= HIDEPID_MAX); > > > +} > > + > > static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param) > > { > > struct proc_fs_context *ctx = fc->fs_private; > > @@ -63,10 +71,9 @@ static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param) > > break; > > > > case Opt_hidepid: > > + if (!valid_hidepid(result.uint_32)) > > + return invalf(fc, "proc: unknown value of hidepid.\n"); > > ctx->hidepid = result.uint_32; > > - if (ctx->hidepid < HIDEPID_OFF || > > - ctx->hidepid > HIDEPID_INVISIBLE) > > - return invalfc(fc, "hidepid value must be between 0 and 2.\n"); > > break; > > > > default: > > diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h > > index 7d852dbca253..21d19353fdc7 100644 > > --- a/include/linux/proc_fs.h > > +++ b/include/linux/proc_fs.h > > @@ -32,6 +32,7 @@ enum { > > HIDEPID_OFF = 0, > > HIDEPID_NO_ACCESS = 1, > > HIDEPID_INVISIBLE = 2, > > + HIDEPID_NOT_PTRACEABLE = 4, /* Limit pids to only ptraceable pids */ > > This isn't a bit field -- shouldn't this be "3"? > > ... > HIDEPID_NOT_PTRACEABLE = 3, > HIDEPID_MAX > > etc? I decided to choose 4 so that if later we need to be able to make a mask. I am not sure that this parameter will not have values that cannot be used together. Since now these parameters are becoming part of the public api, I decided to add flexibility. -- Rgrds, legion