From: Alexey Gladkov <gladkov.alexey@gmail.com> To: LKML <linux-kernel@vger.kernel.org>, Kernel Hardening <kernel-hardening@lists.openwall.com>, Linux API <linux-api@vger.kernel.org>, Linux FS Devel <linux-fsdevel@vger.kernel.org>, Linux Security Module <linux-security-module@vger.kernel.org> Cc: Akinobu Mita <akinobu.mita@gmail.com>, Alexander Viro <viro@zeniv.linux.org.uk>, Alexey Dobriyan <adobriyan@gmail.com>, Alexey Gladkov <gladkov.alexey@gmail.com>, Andrew Morton <akpm@linux-foundation.org>, Andy Lutomirski <luto@kernel.org>, Daniel Micay <danielmicay@gmail.com>, Djalal Harouni <tixxdz@gmail.com>, "Dmitry V . Levin" <ldv@altlinux.org>, "Eric W . Biederman" <ebiederm@xmission.com>, Greg Kroah-Hartman <gregkh@linuxfoundation.org>, Ingo Molnar <mingo@kernel.org>, "J . Bruce Fields" <bfields@fieldses.org>, Jeff Layton <jlayton@poochiereds.net>, Jonathan Corbet <corbet@lwn.net>, Kees Cook <keescook@chromium.org>, Linus Torvalds <torvalds@linux-foundation.org>, Oleg Nesterov <oleg@redhat.com>, Solar Designer <solar@openwall.com> Subject: [PATCH v8 06/11] proc: support mounting procfs instances inside same pid namespace Date: Mon, 10 Feb 2020 16:05:14 +0100 Message-ID: <20200210150519.538333-7-gladkov.alexey@gmail.com> (raw) In-Reply-To: <20200210150519.538333-1-gladkov.alexey@gmail.com> This patch allows to have multiple procfs instances inside the same pid namespace. The aim here is lightweight sandboxes, and to allow that we have to modernize procfs internals. 1) The main aim of this work is to have on embedded systems one supervisor for apps. Right now we have some lightweight sandbox support, however if we create pid namespacess we have to manages all the processes inside too, where our goal is to be able to run a bunch of apps each one inside its own mount namespace without being able to notice each other. We only want to use mount namespaces, and we want procfs to behave more like a real mount point. 2) Linux Security Modules have multiple ptrace paths inside some subsystems, however inside procfs, the implementation does not guarantee that the ptrace() check which triggers the security_ptrace_check() hook will always run. We have the 'hidepid' mount option that can be used to force the ptrace_may_access() check inside has_pid_permissions() to run. The problem is that 'hidepid' is per pid namespace and not attached to the mount point, any remount or modification of 'hidepid' will propagate to all other procfs mounts. This also does not allow to support Yama LSM easily in desktop and user sessions. Yama ptrace scope which restricts ptrace and some other syscalls to be allowed only on inferiors, can be updated to have a per-task context, where the context will be inherited during fork(), clone() and preserved across execve(). If we support multiple private procfs instances, then we may force the ptrace_may_access() on /proc/<pids>/ to always run inside that new procfs instances. This will allow to specifiy on user sessions if we should populate procfs with pids that the user can ptrace or not. By using Yama ptrace scope, some restricted users will only be able to see inferiors inside /proc, they won't even be able to see their other processes. Some software like Chromium, Firefox's crash handler, Wine and others are already using Yama to restrict which processes can be ptracable. With this change this will give the possibility to restrict /proc/<pids>/ but more importantly this will give desktop users a generic and usuable way to specifiy which users should see all processes and which users can not. Side notes: * This covers the lack of seccomp where it is not able to parse arguments, it is easy to install a seccomp filter on direct syscalls that operate on pids, however /proc/<pid>/ is a Linux ABI using filesystem syscalls. With this change LSMs should be able to analyze open/read/write/close... In the new patchset version I removed the 'newinstance' option as Eric W. Biederman suggested. Cc: Kees Cook <keescook@chromium.org> Cc: "Eric W. Biederman" <ebiederm@xmission.com> Signed-off-by: Alexey Gladkov <gladkov.alexey@gmail.com> --- fs/proc/root.c | 41 ++++++++++++++++++----------------------- 1 file changed, 18 insertions(+), 23 deletions(-) diff --git a/fs/proc/root.c b/fs/proc/root.c index efd76c004e86..5d5cba4c899b 100644 --- a/fs/proc/root.c +++ b/fs/proc/root.c @@ -82,7 +82,7 @@ static int proc_parse_param(struct fs_context *fc, struct fs_parameter *param) return 0; } -static void proc_apply_options(struct super_block *s, +static void proc_apply_options(struct proc_fs_info *fs_info, struct fs_context *fc, struct pid_namespace *pid_ns, struct user_namespace *user_ns) @@ -90,15 +90,17 @@ static void proc_apply_options(struct super_block *s, struct proc_fs_context *ctx = fc->fs_private; if (pid_ns->proc_mnt) { - struct proc_fs_info *fs_info = proc_sb_info(pid_ns->proc_mnt->mnt_sb); - proc_fs_set_pid_gid(ctx->fs_info, proc_fs_pid_gid(fs_info)); - proc_fs_set_hide_pid(ctx->fs_info, proc_fs_hide_pid(fs_info)); + struct proc_fs_info *pidns_fs_info = proc_sb_info(pid_ns->proc_mnt->mnt_sb); + + proc_fs_set_pid_gid(fs_info, proc_fs_pid_gid(pidns_fs_info)); + proc_fs_set_hide_pid(fs_info, proc_fs_hide_pid(pidns_fs_info)); } if (ctx->mask & (1 << Opt_gid)) - proc_fs_set_pid_gid(ctx->fs_info, make_kgid(user_ns, ctx->gid)); + proc_fs_set_pid_gid(fs_info, make_kgid(user_ns, ctx->gid)); + if (ctx->mask & (1 << Opt_hidepid)) - proc_fs_set_hide_pid(ctx->fs_info, ctx->hidepid); + proc_fs_set_hide_pid(fs_info, ctx->hidepid); } static int proc_fill_super(struct super_block *s, struct fs_context *fc) @@ -108,7 +110,7 @@ static int proc_fill_super(struct super_block *s, struct fs_context *fc) struct inode *root_inode; int ret; - proc_apply_options(s, fc, pid_ns, current_user_ns()); + proc_apply_options(ctx->fs_info, fc, pid_ns, current_user_ns()); /* User space would break if executables or devices appear on proc */ s->s_iflags |= SB_I_USERNS_VISIBLE | SB_I_NOEXEC | SB_I_NODEV; @@ -118,6 +120,7 @@ static int proc_fill_super(struct super_block *s, struct fs_context *fc) s->s_magic = PROC_SUPER_MAGIC; s->s_op = &proc_sops; s->s_time_gran = 1; + s->s_fs_info = ctx->fs_info; /* * procfs isn't actually a stacking filesystem; however, there is @@ -157,15 +160,13 @@ static int proc_reconfigure(struct fs_context *fc) sync_filesystem(sb); - proc_apply_options(sb, fc, pid, current_user_ns()); + proc_apply_options(fs_info, fc, pid, current_user_ns()); return 0; } static int proc_get_tree(struct fs_context *fc) { - struct proc_fs_context *ctx = fc->fs_private; - - return get_tree_keyed(fc, proc_fill_super, ctx->fs_info); + return get_tree_nodev(fc, proc_fill_super); } static void proc_fs_context_free(struct fs_context *fc) @@ -186,25 +187,19 @@ static const struct fs_context_operations proc_fs_context_ops = { static int proc_init_fs_context(struct fs_context *fc) { struct proc_fs_context *ctx; - struct pid_namespace *pid_ns; ctx = kzalloc(sizeof(struct proc_fs_context), GFP_KERNEL); if (!ctx) return -ENOMEM; - pid_ns = get_pid_ns(task_active_pid_ns(current)); - - if (!pid_ns->proc_mnt) { - ctx->fs_info = kzalloc(sizeof(struct proc_fs_info), GFP_KERNEL); - if (!ctx->fs_info) { - kfree(ctx); - return -ENOMEM; - } - ctx->fs_info->pid_ns = pid_ns; - } else { - ctx->fs_info = proc_sb_info(pid_ns->proc_mnt->mnt_sb); + ctx->fs_info = kzalloc(sizeof(struct proc_fs_info), GFP_KERNEL); + if (!ctx->fs_info) { + kfree(ctx); + return -ENOMEM; } + ctx->fs_info->pid_ns = get_pid_ns(task_active_pid_ns(current)); + put_user_ns(fc->user_ns); fc->user_ns = get_user_ns(ctx->fs_info->pid_ns->user_ns); fc->fs_private = ctx; -- 2.24.1
next prev parent reply index Thread overview: 85+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-02-10 15:05 [PATCH v8 00/11] proc: modernize proc to support multiple private instances Alexey Gladkov 2020-02-10 15:05 ` [PATCH v8 01/11] proc: Rename struct proc_fs_info to proc_fs_opts Alexey Gladkov 2020-02-10 15:05 ` [PATCH v8 02/11] proc: add proc_fs_info struct to store proc information Alexey Gladkov 2020-02-10 15:05 ` [PATCH v8 03/11] proc: move /proc/{self|thread-self} dentries to proc_fs_info Alexey Gladkov 2020-02-10 18:23 ` Andy Lutomirski 2020-02-12 15:00 ` Alexey Gladkov 2020-02-10 15:05 ` [PATCH v8 04/11] proc: move hide_pid, pid_gid from pid_namespace " Alexey Gladkov 2020-02-10 15:05 ` [PATCH v8 05/11] proc: add helpers to set and get proc hidepid and gid mount options Alexey Gladkov 2020-02-10 18:30 ` Andy Lutomirski 2020-02-12 14:57 ` Alexey Gladkov 2020-02-10 15:05 ` Alexey Gladkov [this message] 2020-02-10 15:05 ` [PATCH v8 07/11] proc: flush task dcache entries from all procfs instances Alexey Gladkov 2020-02-10 17:46 ` Linus Torvalds 2020-02-10 19:23 ` Al Viro 2020-02-11 1:36 ` Eric W. Biederman 2020-02-11 4:01 ` Eric W. Biederman 2020-02-12 14:49 ` Alexey Gladkov 2020-02-12 14:59 ` Eric W. Biederman 2020-02-12 17:08 ` Alexey Gladkov 2020-02-12 18:45 ` Linus Torvalds 2020-02-12 19:16 ` Eric W. Biederman 2020-02-12 19:49 ` Linus Torvalds 2020-02-12 20:03 ` Al Viro 2020-02-12 20:35 ` Linus Torvalds 2020-02-12 20:38 ` Al Viro 2020-02-12 20:41 ` Al Viro 2020-02-12 21:02 ` Linus Torvalds 2020-02-12 21:46 ` Eric W. Biederman 2020-02-13 0:48 ` Linus Torvalds 2020-02-13 4:37 ` Eric W. Biederman 2020-02-13 5:55 ` Al Viro 2020-02-13 21:30 ` Linus Torvalds 2020-02-13 22:23 ` Al Viro 2020-02-13 22:47 ` Linus Torvalds 2020-02-14 14:15 ` Eric W. Biederman 2020-02-14 3:48 ` Eric W. Biederman 2020-02-20 20:46 ` [PATCH 0/7] proc: Dentry flushing without proc_mnt Eric W. Biederman 2020-02-20 20:47 ` [PATCH 1/7] proc: Rename in proc_inode rename sysctl_inodes sibling_inodes Eric W. Biederman 2020-02-20 20:48 ` [PATCH 2/7] proc: Generalize proc_sys_prune_dcache into proc_prune_siblings_dcache Eric W. Biederman 2020-02-20 20:49 ` [PATCH 3/7] proc: Mov rcu_read_(lock|unlock) in proc_prune_siblings_dcache Eric W. Biederman 2020-02-20 22:33 ` Linus Torvalds 2020-02-20 20:49 ` [PATCH 4/7] proc: Use d_invalidate " Eric W. Biederman 2020-02-20 22:43 ` Linus Torvalds 2020-02-20 22:54 ` Al Viro 2020-02-20 23:00 ` Linus Torvalds 2020-02-20 23:03 ` Al Viro 2020-02-20 23:39 ` Eric W. Biederman 2020-02-20 20:51 ` [PATCH 5/7] proc: Clear the pieces of proc_inode that proc_evict_inode cares about Eric W. Biederman 2020-02-20 20:52 ` [PATCH 6/7] proc: Use a list of inodes to flush from proc Eric W. Biederman 2020-02-20 20:52 ` [PATCH 7/7] proc: Ensure we see the exit of each process tid exactly once Eric W. Biederman 2020-02-21 16:50 ` Oleg Nesterov 2020-02-22 15:46 ` Eric W. Biederman 2020-02-20 23:02 ` [PATCH 0/7] proc: Dentry flushing without proc_mnt Linus Torvalds 2020-02-20 23:07 ` Al Viro 2020-02-20 23:37 ` Eric W. Biederman 2020-02-24 16:25 ` [PATCH v2 0/6] " Eric W. Biederman 2020-02-24 16:26 ` [PATCH v2 1/6] proc: Rename in proc_inode rename sysctl_inodes sibling_inodes Eric W. Biederman 2020-02-24 16:27 ` [PATCH v2 2/6] proc: Generalize proc_sys_prune_dcache into proc_prune_siblings_dcache Eric W. Biederman 2020-02-24 16:27 ` [PATCH v2 3/6] proc: In proc_prune_siblings_dcache cache an aquired super block Eric W. Biederman 2020-02-24 16:28 ` [PATCH v2 4/6] proc: Use d_invalidate in proc_prune_siblings_dcache Eric W. Biederman 2020-02-24 16:28 ` [PATCH v2 5/6] proc: Clear the pieces of proc_inode that proc_evict_inode cares about Eric W. Biederman 2020-02-24 16:29 ` [PATCH v2 6/6] proc: Use a list of inodes to flush from proc Eric W. Biederman 2020-02-28 20:17 ` [PATCH 0/3] proc: Actually honor the mount options Eric W. Biederman 2020-02-28 20:18 ` [PATCH 1/3] uml: Don't consult current to find the proc_mnt in mconsole_proc Eric W. Biederman 2020-02-28 20:18 ` [PATCH 2/3] uml: Create a private mount of proc for mconsole Eric W. Biederman 2020-02-28 20:30 ` Christian Brauner 2020-02-28 21:28 ` Eric W. Biederman 2020-02-28 21:59 ` Christian Brauner 2020-02-28 20:19 ` [PATCH 3/3] proc: Remove the now unnecessary internal mount of proc Eric W. Biederman 2020-02-28 20:39 ` Christian Brauner 2020-02-28 21:40 ` Eric W. Biederman 2020-02-28 22:34 ` [PATCH 4/3] pid: Improve the comment about waiting in zap_pid_ns_processes Eric W. Biederman 2020-02-29 2:59 ` Christian Brauner 2020-02-14 3:49 ` [PATCH v8 07/11] proc: flush task dcache entries from all procfs instances Eric W. Biederman 2020-02-12 19:47 ` Al Viro 2020-02-11 22:45 ` Al Viro 2020-02-12 14:26 ` Alexey Gladkov 2020-02-10 15:05 ` [PATCH v8 08/11] proc: instantiate only pids that we can ptrace on 'hidepid=4' mount option Alexey Gladkov 2020-02-10 16:29 ` Jordan Glover 2020-02-12 14:34 ` Alexey Gladkov 2020-02-10 15:05 ` [PATCH v8 09/11] proc: add option to mount only a pids subset Alexey Gladkov 2020-02-10 15:05 ` [PATCH v8 10/11] docs: proc: add documentation for "hidepid=4" and "subset=pidfs" options and new mount behavior Alexey Gladkov 2020-02-10 18:29 ` Andy Lutomirski 2020-02-12 16:03 ` Alexey Gladkov 2020-02-10 15:05 ` [PATCH v8 11/11] proc: Move hidepid values to uapi as they are user interface to mount Alexey Gladkov
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