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=-22.3 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham 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 77B06C04FF3 for ; Mon, 24 May 2021 10:03:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 47B66610FA for ; Mon, 24 May 2021 10:03:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232422AbhEXKE1 (ORCPT ); Mon, 24 May 2021 06:04:27 -0400 Received: from mx2.suse.de ([195.135.220.15]:42878 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232511AbhEXKEZ (ORCPT ); Mon, 24 May 2021 06:04:25 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_rsa; t=1621850571; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=HzX6CgeTXyOpjH0UZe1hWTvDCF2rtL9Vv0VHYgBHrtk=; b=gHFLg8M5STA/eba6lvF+95EwRaFLJJQTUlEXY7Mot/I5lpILO9boToRUr0H5D4XNSi1oou gk7HmTKIDKsPLNe5bxT0vZ9yEQ5t+LfwrpD+pCgasCry8TeLwUAFquu3Rj/wQfL0pCYrwe RFg/sXXUMppVX/iebW0HAlMD7v6KrEs= DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=suse.cz; s=susede2_ed25519; t=1621850571; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=HzX6CgeTXyOpjH0UZe1hWTvDCF2rtL9Vv0VHYgBHrtk=; b=JiuAScxLWAptvdlq8bk98aqFOrBGDY6sq38yKOrBnzz00BYjp6pJWyYwnz706tkIohpN8A m1yBE5Dd96cA5qAQ== Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 79CBCAB6D; Mon, 24 May 2021 10:02:51 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 547701F2CA2; Mon, 24 May 2021 12:02:51 +0200 (CEST) Date: Mon, 24 May 2021 12:02:51 +0200 From: Jan Kara To: Amir Goldstein Cc: Jan Kara , Matthew Bobrowski , linux-fsdevel@vger.kernel.org Subject: Re: [PATCH] fanotify: fix permission model of unprivileged group Message-ID: <20210524100251.GJ32705@quack2.suse.cz> References: <20210522091916.196741-1-amir73il@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210522091916.196741-1-amir73il@gmail.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Sat 22-05-21 12:19:16, Amir Goldstein wrote: > Reporting event->pid should depend on the privileges of the user that > initialized the group, not the privileges of the user reading the > events. > > Use an internal group flag FANOTIFY_UNPRIV to record the fact the the > group was initialized by an unprivileged user. > > To be on the safe side, the premissions to setup filesystem and mount > marks now require that both the user that initialized the group and > the user setting up the mark have CAP_SYS_ADMIN. > > Fixes: 7cea2a3c505e ("fanotify: support limited functionality for unprivileged users") > Signed-off-by: Amir Goldstein > --- > > Jan, > > The original RFC [1] used the internal flag to check permissions for: > 1. Reporting event->pid > 2. Reporting event->fd > 3. Setting up sb/mount marks > > Although we discussed only adding the check for #1, I left all those > checks. > > The check for #2 is redundant, but it feels safer to be > defensive to protect against leaked fds. > > The check for #3 was added in addition to the existing permission checks > because it feels right. Let me know if you disagree. > > I've adjusted Matthew's LTP test [2] to check case #1. Thanks! Modulo those language nits from Matthew the patch looks good to me. Honza > [1] https://lore.kernel.org/linux-fsdevel/20210124184204.899729-3-amir73il@gmail.com/ > [1] https://github.com/amir73il/ltp/commits/fanotify_unpriv > > fs/notify/fanotify/fanotify_user.c | 30 ++++++++++++++++++++++++------ > fs/notify/fdinfo.c | 2 +- > include/linux/fanotify.h | 4 ++++ > 3 files changed, 29 insertions(+), 7 deletions(-) > > diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c > index 71fefb30e015..7df6cba4a06d 100644 > --- a/fs/notify/fanotify/fanotify_user.c > +++ b/fs/notify/fanotify/fanotify_user.c > @@ -424,11 +424,18 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group, > * events generated by the listener process itself, without disclosing > * the pids of other processes. > */ > - if (!capable(CAP_SYS_ADMIN) && > + if (FAN_GROUP_FLAG(group, FANOTIFY_UNPRIV) && > task_tgid(current) != event->pid) > metadata.pid = 0; > > - if (path && path->mnt && path->dentry) { > + /* > + * For now, we require fid mode for unprivileged listener, which does > + * record path events, but keep this check for safety in case we want > + * to allow unprivileged listener to get events with no fd and no fid > + * in the future. > + */ > + if (!FAN_GROUP_FLAG(group, FANOTIFY_UNPRIV) && > + path && path->mnt && path->dentry) { > fd = create_fd(group, path, &f); > if (fd < 0) > return fd; > @@ -1040,6 +1047,7 @@ SYSCALL_DEFINE2(fanotify_init, unsigned int, flags, unsigned int, event_f_flags) > int f_flags, fd; > unsigned int fid_mode = flags & FANOTIFY_FID_BITS; > unsigned int class = flags & FANOTIFY_CLASS_BITS; > + unsigned int internal_flags = 0; > > pr_debug("%s: flags=%x event_f_flags=%x\n", > __func__, flags, event_f_flags); > @@ -1053,6 +1061,13 @@ SYSCALL_DEFINE2(fanotify_init, unsigned int, flags, unsigned int, event_f_flags) > */ > if ((flags & FANOTIFY_ADMIN_INIT_FLAGS) || !fid_mode) > return -EPERM; > + > + /* > + * We set the internal flag FANOTIFY_UNPRIV on the group, so we > + * know that we need to limit setting mount/filesystem marks on > + * this group and avoid providing pid and open fd in the event. > + */ > + internal_flags |= FANOTIFY_UNPRIV; > } > > #ifdef CONFIG_AUDITSYSCALL > @@ -1105,7 +1120,7 @@ SYSCALL_DEFINE2(fanotify_init, unsigned int, flags, unsigned int, event_f_flags) > goto out_destroy_group; > } > > - group->fanotify_data.flags = flags; > + group->fanotify_data.flags = flags | internal_flags; > group->memcg = get_mem_cgroup_from_mm(current->mm); > > group->fanotify_data.merge_hash = fanotify_alloc_merge_hash(); > @@ -1305,11 +1320,13 @@ static int do_fanotify_mark(int fanotify_fd, unsigned int flags, __u64 mask, > group = f.file->private_data; > > /* > - * An unprivileged user is not allowed to watch a mount point nor > - * a filesystem. > + * An unprivileged user is not allowed to setup mount point nor > + * filesystem marks. It is not allowed to setup those marks for > + * a group that was initialized by an unprivileged user. > */ > ret = -EPERM; > - if (!capable(CAP_SYS_ADMIN) && > + if ((!capable(CAP_SYS_ADMIN) || > + FAN_GROUP_FLAG(group, FANOTIFY_UNPRIV)) && > mark_type != FAN_MARK_INODE) > goto fput_and_out; > > @@ -1460,6 +1477,7 @@ static int __init fanotify_user_setup(void) > max_marks = clamp(max_marks, FANOTIFY_OLD_DEFAULT_MAX_MARKS, > FANOTIFY_DEFAULT_MAX_USER_MARKS); > > + BUILD_BUG_ON(FANOTIFY_INIT_FLAGS & FANOTIFY_INTERNAL_FLAGS); > BUILD_BUG_ON(HWEIGHT32(FANOTIFY_INIT_FLAGS) != 10); > BUILD_BUG_ON(HWEIGHT32(FANOTIFY_MARK_FLAGS) != 9); > > diff --git a/fs/notify/fdinfo.c b/fs/notify/fdinfo.c > index a712b2aaa9ac..57f0d5d9f934 100644 > --- a/fs/notify/fdinfo.c > +++ b/fs/notify/fdinfo.c > @@ -144,7 +144,7 @@ void fanotify_show_fdinfo(struct seq_file *m, struct file *f) > struct fsnotify_group *group = f->private_data; > > seq_printf(m, "fanotify flags:%x event-flags:%x\n", > - group->fanotify_data.flags, > + group->fanotify_data.flags & FANOTIFY_INIT_FLAGS, > group->fanotify_data.f_flags); > > show_fdinfo(m, f, fanotify_fdinfo); > diff --git a/include/linux/fanotify.h b/include/linux/fanotify.h > index bad41bcb25df..f277d1c4e6b8 100644 > --- a/include/linux/fanotify.h > +++ b/include/linux/fanotify.h > @@ -51,6 +51,10 @@ extern struct ctl_table fanotify_table[]; /* for sysctl */ > #define FANOTIFY_INIT_FLAGS (FANOTIFY_ADMIN_INIT_FLAGS | \ > FANOTIFY_USER_INIT_FLAGS) > > +/* Internal flags */ > +#define FANOTIFY_UNPRIV 0x80000000 > +#define FANOTIFY_INTERNAL_FLAGS (FANOTIFY_UNPRIV) > + > #define FANOTIFY_MARK_TYPE_BITS (FAN_MARK_INODE | FAN_MARK_MOUNT | \ > FAN_MARK_FILESYSTEM) > > -- > 2.31.1 > -- Jan Kara SUSE Labs, CR