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[2620:137:e000::1:20]) by mx.google.com with ESMTP id 140-20020a630092000000b004ad157c46bbsi39759320pga.649.2023.01.19.09.13.22; Thu, 19 Jan 2023 09:13:34 -0800 (PST) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@redhat.com header.s=mimecast20190719 header.b=OklQWbLy; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229564AbjASRI3 (ORCPT + 99 others); Thu, 19 Jan 2023 12:08:29 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:51644 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229487AbjASRI1 (ORCPT ); Thu, 19 Jan 2023 12:08:27 -0500 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AB4B28CE40 for ; Thu, 19 Jan 2023 09:07:32 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1674148051; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=SQEjHq6mfWWCvha2uWrGb+PpWDRieTJfTi4g/4DmaJI=; b=OklQWbLyobrEhkkoFzk+Lq6+aEIADkgIzP/YJF9NFLyvjzxSWLS/t+uZj32TBQdivxdzpi ERkoK+ifmZICzCfjSnanDdXeBShArVRrzakIA8nPXn2uqM1iPA1Gt0BxoNP6b2870/KrQO h7JTNBavdNCF39Hj6sDhhs6bLR4k3jo= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-354-r7fJ_dc2PoKXLYzY3xkg2g-1; Thu, 19 Jan 2023 12:07:29 -0500 X-MC-Unique: r7fJ_dc2PoKXLYzY3xkg2g-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id B5C9985C074; Thu, 19 Jan 2023 17:07:28 +0000 (UTC) Received: from lithium.redhat.com (unknown [10.39.195.23]) by smtp.corp.redhat.com (Postfix) with ESMTP id 5AAB82026D76; Thu, 19 Jan 2023 17:07:26 +0000 (UTC) From: Giuseppe Scrivano To: linux-kernel@vger.kernel.org Cc: keescook@chromium.org, bristot@redhat.com, ebiederm@xmission.com, brauner@kernel.org, cyphar@cyphar.com, bmasney@redhat.com, viro@zeniv.linux.org.uk, alexl@redhat.com, peterz@infradead.org, gscrivan@redhat.com Subject: [PATCH v2 1/2] exec: add PR_HIDE_SELF_EXE prctl Date: Thu, 19 Jan 2023 18:07:17 +0100 Message-Id: <20230119170718.3129938-1-gscrivan@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.4 X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, RCVD_IN_MSPIKE_H2,SPF_HELO_NONE,SPF_NONE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1755471847999800971?= X-GMAIL-MSGID: =?utf-8?q?1755471847999800971?= This patch adds a new prctl called PR_HIDE_SELF_EXE which allows processes to hide their own /proc/*/exe file. When this prctl is used, every access to /proc/*/exe for the calling process will fail with ENOENT. This is useful for preventing issues like CVE-2019-5736, where an attacker can gain host root access by overwriting the binary in OCI runtimes through file-descriptor mishandling in containers. The current fix for CVE-2019-5736 is to create a read-only copy or a bind-mount of the current executable, and then re-exec the current process. With the new prctl, the read-only copy or bind-mount copy is not needed anymore. While map_files/ also might contain symlinks to files in host, proc_map_files_get_link() permissions checks are already sufficient. Signed-off-by: Giuseppe Scrivano --- fs/exec.c | 1 + fs/proc/base.c | 8 +++++--- include/linux/sched.h | 5 +++++ include/uapi/linux/prctl.h | 3 +++ kernel/sys.c | 9 +++++++++ tools/include/uapi/linux/prctl.h | 3 +++ 6 files changed, 26 insertions(+), 3 deletions(-) v1: https://lkml.org/lkml/2023/1/4/334 Differences from v1: - amended more information in the commit message wrt map_files not requiring the same protection. - changed the test to verify PR_HIDE_SELF_EXE cannot be unset after a fork. diff --git a/fs/exec.c b/fs/exec.c index ab913243a367..5a5dd964c3a3 100644 --- a/fs/exec.c +++ b/fs/exec.c @@ -1855,6 +1855,7 @@ static int bprm_execve(struct linux_binprm *bprm, /* execve succeeded */ current->fs->in_exec = 0; current->in_execve = 0; + task_clear_hide_self_exe(current); rseq_execve(current); acct_update_integrals(current); task_numa_free(current, false); diff --git a/fs/proc/base.c b/fs/proc/base.c index 9e479d7d202b..959968e2da0d 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -1723,19 +1723,21 @@ static int proc_exe_link(struct dentry *dentry, struct path *exe_path) { struct task_struct *task; struct file *exe_file; + long hide_self_exe; task = get_proc_task(d_inode(dentry)); if (!task) return -ENOENT; exe_file = get_task_exe_file(task); + hide_self_exe = task_hide_self_exe(task); put_task_struct(task); - if (exe_file) { + if (exe_file && !hide_self_exe) { *exe_path = exe_file->f_path; path_get(&exe_file->f_path); fput(exe_file); return 0; - } else - return -ENOENT; + } + return -ENOENT; } static const char *proc_pid_get_link(struct dentry *dentry, diff --git a/include/linux/sched.h b/include/linux/sched.h index 853d08f7562b..8db32d5fc285 100644 --- a/include/linux/sched.h +++ b/include/linux/sched.h @@ -1790,6 +1790,7 @@ static __always_inline bool is_percpu_thread(void) #define PFA_SPEC_IB_DISABLE 5 /* Indirect branch speculation restricted */ #define PFA_SPEC_IB_FORCE_DISABLE 6 /* Indirect branch speculation permanently restricted */ #define PFA_SPEC_SSB_NOEXEC 7 /* Speculative Store Bypass clear on execve() */ +#define PFA_HIDE_SELF_EXE 8 /* Hide /proc/self/exe for the process */ #define TASK_PFA_TEST(name, func) \ static inline bool task_##func(struct task_struct *p) \ @@ -1832,6 +1833,10 @@ TASK_PFA_CLEAR(SPEC_IB_DISABLE, spec_ib_disable) TASK_PFA_TEST(SPEC_IB_FORCE_DISABLE, spec_ib_force_disable) TASK_PFA_SET(SPEC_IB_FORCE_DISABLE, spec_ib_force_disable) +TASK_PFA_TEST(HIDE_SELF_EXE, hide_self_exe) +TASK_PFA_SET(HIDE_SELF_EXE, hide_self_exe) +TASK_PFA_CLEAR(HIDE_SELF_EXE, hide_self_exe) + static inline void current_restore_flags(unsigned long orig_flags, unsigned long flags) { diff --git a/include/uapi/linux/prctl.h b/include/uapi/linux/prctl.h index a5e06dcbba13..f12f3df12468 100644 --- a/include/uapi/linux/prctl.h +++ b/include/uapi/linux/prctl.h @@ -284,4 +284,7 @@ struct prctl_mm_map { #define PR_SET_VMA 0x53564d41 # define PR_SET_VMA_ANON_NAME 0 +#define PR_SET_HIDE_SELF_EXE 65 +#define PR_GET_HIDE_SELF_EXE 66 + #endif /* _LINUX_PRCTL_H */ diff --git a/kernel/sys.c b/kernel/sys.c index 5fd54bf0e886..e992f1b72973 100644 --- a/kernel/sys.c +++ b/kernel/sys.c @@ -2626,6 +2626,15 @@ SYSCALL_DEFINE5(prctl, int, option, unsigned long, arg2, unsigned long, arg3, case PR_SET_VMA: error = prctl_set_vma(arg2, arg3, arg4, arg5); break; + case PR_SET_HIDE_SELF_EXE: + if (arg2 != 1 || arg3 || arg4 || arg5) + return -EINVAL; + task_set_hide_self_exe(current); + break; + case PR_GET_HIDE_SELF_EXE: + if (arg2 || arg3 || arg4 || arg5) + return -EINVAL; + return task_hide_self_exe(current) ? 1 : 0; default: error = -EINVAL; break; diff --git a/tools/include/uapi/linux/prctl.h b/tools/include/uapi/linux/prctl.h index a5e06dcbba13..f12f3df12468 100644 --- a/tools/include/uapi/linux/prctl.h +++ b/tools/include/uapi/linux/prctl.h @@ -284,4 +284,7 @@ struct prctl_mm_map { #define PR_SET_VMA 0x53564d41 # define PR_SET_VMA_ANON_NAME 0 +#define PR_SET_HIDE_SELF_EXE 65 +#define PR_GET_HIDE_SELF_EXE 66 + #endif /* _LINUX_PRCTL_H */