From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id EB341EEC8; Tue, 8 Oct 2024 12:18:14 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728389895; cv=none; b=a9QDZQZZkgHnJnLiDwj6tcysIE7p6LdJnHgeFmA/YWZl/QxFghTtWpMsYnWuD4vrey3LwYxeu4PWF7v+ctweNpbSKiYhvr2QqE0GoR4dSkqv8d8+1IWn59nN9SSohPLw5iPnaYCTm8bss9ApFWHotWjUEmZ25HJ8g3PE8bzZXXM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1728389895; c=relaxed/simple; bh=j3m0Le1ryw+PN43RGoewbj3cupxqPwxLqyMRjRQaj0Q=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=lPr5Za+lxkhJ7/crzZzMJTJ9mb5bxmxvwN36ThVAGjA4elBUGIaOQRFawNfcnw24RvO6MkbzLkHOViH5ntI9JyN+x37DMtBr+57IcoI/c1jF5L6Hclfp+C1jX9ikf/H890lAAzOmFsaRkwXv3YA/HpLLW6r19hMAzFnXILmFkEM= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=H+eKLSlf; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="H+eKLSlf" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6C080C4CECC; Tue, 8 Oct 2024 12:18:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1728389894; bh=j3m0Le1ryw+PN43RGoewbj3cupxqPwxLqyMRjRQaj0Q=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=H+eKLSlferJuwKHlPH5b320O2l9rQydF+eg0kl4JV95Z4rkdRPl1C2FCfEta69V2q oHo3x+dDViEpzqcJYEvTZguLqj+nod+h71vJrkFkCT/LnH87R2oJ4fX5QMKhrwMZb0 bV91ZVM+IaUm6HhH9SsU/fFUAd4xLTj5eJ/xALwE= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Doug Anderson , Jeff Xu , Jann Horn , Kees Cook , Ard Biesheuvel , Christian Brauner , Linus Torvalds , Adrian Ratiu , Sasha Levin Subject: [PATCH 6.10 121/482] proc: add config & param to block forcing mem writes Date: Tue, 8 Oct 2024 14:03:04 +0200 Message-ID: <20241008115653.068115041@linuxfoundation.org> X-Mailer: git-send-email 2.46.2 In-Reply-To: <20241008115648.280954295@linuxfoundation.org> References: <20241008115648.280954295@linuxfoundation.org> User-Agent: quilt/0.67 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.10-stable review patch. If anyone has any objections, please let me know. ------------------ From: Adrian Ratiu [ Upstream commit 41e8149c8892ed1962bd15350b3c3e6e90cba7f4 ] This adds a Kconfig option and boot param to allow removing the FOLL_FORCE flag from /proc/pid/mem write calls because it can be abused. The traditional forcing behavior is kept as default because it can break GDB and some other use cases. Previously we tried a more sophisticated approach allowing distributions to fine-tune /proc/pid/mem behavior, however that got NAK-ed by Linus [1], who prefers this simpler approach with semantics also easier to understand for users. Link: https://lore.kernel.org/lkml/CAHk-=wiGWLChxYmUA5HrT5aopZrB7_2VTa0NLZcxORgkUe5tEQ@mail.gmail.com/ [1] Cc: Doug Anderson Cc: Jeff Xu Cc: Jann Horn Cc: Kees Cook Cc: Ard Biesheuvel Cc: Christian Brauner Suggested-by: Linus Torvalds Signed-off-by: Linus Torvalds Signed-off-by: Adrian Ratiu Link: https://lore.kernel.org/r/20240802080225.89408-1-adrian.ratiu@collabora.com Signed-off-by: Christian Brauner Signed-off-by: Sasha Levin --- .../admin-guide/kernel-parameters.txt | 10 +++ fs/proc/base.c | 61 ++++++++++++++++++- security/Kconfig | 32 ++++++++++ 3 files changed, 102 insertions(+), 1 deletion(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index c82446cef8e21..2c8e062eb2ce5 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -4791,6 +4791,16 @@ printk.time= Show timing data prefixed to each printk message line Format: (1/Y/y=enable, 0/N/n=disable) + proc_mem.force_override= [KNL] + Format: {always | ptrace | never} + Traditionally /proc/pid/mem allows memory permissions to be + overridden without restrictions. This option may be set to + restrict that. Can be one of: + - 'always': traditional behavior always allows mem overrides. + - 'ptrace': only allow mem overrides for active ptracers. + - 'never': never allow mem overrides. + If not specified, default is the CONFIG_PROC_MEM_* choice. + processor.max_cstate= [HW,ACPI] Limit processor to maximum C-state max_cstate=9 overrides any DMI blacklist limit. diff --git a/fs/proc/base.c b/fs/proc/base.c index 72a1acd03675c..f389c69767fa5 100644 --- a/fs/proc/base.c +++ b/fs/proc/base.c @@ -85,6 +85,7 @@ #include #include #include +#include #include #include #include @@ -117,6 +118,40 @@ static u8 nlink_tid __ro_after_init; static u8 nlink_tgid __ro_after_init; +enum proc_mem_force { + PROC_MEM_FORCE_ALWAYS, + PROC_MEM_FORCE_PTRACE, + PROC_MEM_FORCE_NEVER +}; + +static enum proc_mem_force proc_mem_force_override __ro_after_init = + IS_ENABLED(CONFIG_PROC_MEM_NO_FORCE) ? PROC_MEM_FORCE_NEVER : + IS_ENABLED(CONFIG_PROC_MEM_FORCE_PTRACE) ? PROC_MEM_FORCE_PTRACE : + PROC_MEM_FORCE_ALWAYS; + +static const struct constant_table proc_mem_force_table[] __initconst = { + { "always", PROC_MEM_FORCE_ALWAYS }, + { "ptrace", PROC_MEM_FORCE_PTRACE }, + { "never", PROC_MEM_FORCE_NEVER }, + { } +}; + +static int __init early_proc_mem_force_override(char *buf) +{ + if (!buf) + return -EINVAL; + + /* + * lookup_constant() defaults to proc_mem_force_override to preseve + * the initial Kconfig choice in case an invalid param gets passed. + */ + proc_mem_force_override = lookup_constant(proc_mem_force_table, + buf, proc_mem_force_override); + + return 0; +} +early_param("proc_mem.force_override", early_proc_mem_force_override); + struct pid_entry { const char *name; unsigned int len; @@ -835,6 +870,28 @@ static int mem_open(struct inode *inode, struct file *file) return ret; } +static bool proc_mem_foll_force(struct file *file, struct mm_struct *mm) +{ + struct task_struct *task; + bool ptrace_active = false; + + switch (proc_mem_force_override) { + case PROC_MEM_FORCE_NEVER: + return false; + case PROC_MEM_FORCE_PTRACE: + task = get_proc_task(file_inode(file)); + if (task) { + ptrace_active = READ_ONCE(task->ptrace) && + READ_ONCE(task->mm) == mm && + READ_ONCE(task->parent) == current; + put_task_struct(task); + } + return ptrace_active; + default: + return true; + } +} + static ssize_t mem_rw(struct file *file, char __user *buf, size_t count, loff_t *ppos, int write) { @@ -855,7 +912,9 @@ static ssize_t mem_rw(struct file *file, char __user *buf, if (!mmget_not_zero(mm)) goto free; - flags = FOLL_FORCE | (write ? FOLL_WRITE : 0); + flags = write ? FOLL_WRITE : 0; + if (proc_mem_foll_force(file, mm)) + flags |= FOLL_FORCE; while (count > 0) { size_t this_len = min_t(size_t, count, PAGE_SIZE); diff --git a/security/Kconfig b/security/Kconfig index 412e76f1575d0..a93c1a9b7c283 100644 --- a/security/Kconfig +++ b/security/Kconfig @@ -19,6 +19,38 @@ config SECURITY_DMESG_RESTRICT If you are unsure how to answer this question, answer N. +choice + prompt "Allow /proc/pid/mem access override" + default PROC_MEM_ALWAYS_FORCE + help + Traditionally /proc/pid/mem allows users to override memory + permissions for users like ptrace, assuming they have ptrace + capability. + + This allows people to limit that - either never override, or + require actual active ptrace attachment. + + Defaults to the traditional behavior (for now) + +config PROC_MEM_ALWAYS_FORCE + bool "Traditional /proc/pid/mem behavior" + help + This allows /proc/pid/mem accesses to override memory mapping + permissions if you have ptrace access rights. + +config PROC_MEM_FORCE_PTRACE + bool "Require active ptrace() use for access override" + help + This allows /proc/pid/mem accesses to override memory mapping + permissions for active ptracers like gdb. + +config PROC_MEM_NO_FORCE + bool "Never" + help + Never override memory mapping permissions + +endchoice + config SECURITY bool "Enable different security models" depends on SYSFS -- 2.43.0