Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755462Ab1BHC43 (ORCPT ); Mon, 7 Feb 2011 21:56:29 -0500 Received: from mx1.redhat.com ([209.132.183.28]:24888 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754153Ab1BHC41 (ORCPT ); Mon, 7 Feb 2011 21:56:27 -0500 Subject: Re: [PATCH] System Wide Capability Bounding Set From: Eric Paris To: "Andrew G. Morgan" Cc: "Serge E. Hallyn" , Steve Grubb , "Serge E. Hallyn" , linux-kernel@vger.kernel.org, linux-security-module@vger.kernel.org Date: Mon, 07 Feb 2011 21:55:57 -0500 In-Reply-To: References: <1294266337.3237.45.camel@localhost.localdomain> <201101270942.07689.sgrubb@redhat.com> <20110128184901.GA5134@localhost> <201101281410.29794.sgrubb@redhat.com> <20110128193809.GB8854@localhost> <1296584221.3145.12.camel@localhost.localdomain> <20110201212605.GB5294@localhost> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Message-ID: <1297133758.2323.5.camel@localhost.localdomain> Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 6591 Lines: 234 On Tue, 2011-02-01 at 20:02 -0800, Andrew G. Morgan wrote: > In this case, I would like to suggest what you need is a user > configurable state for kernel threads to launch helper programs - a > kernel side equivalent to Sergey's wrapper idea. I continue to > dislike the global bounding set idea, but I would support a base > credential set for this kthread launcher. I'd include pI, bset, and > securebits and uid as something your initrd could initialize away from > their default values for kernel launched helper binaries. I'd prefer > it if you allowed the regular capability convolution rules to apply > and propagate this bounding set for all kernel launched binaries, and > also add the relevant code to init to enforce your desired bounding > set for init parented processes. > >> Or an interface in which I can force things out of the bset and pI of > >> other tasks? Possibly the interface could be specific to the "khelper" > >> thread? > > > > No no no no no :) Below is what I'm working on. I've asked dhowells to review the creds code, since commit_creds() does not take const. Maybe that's just an oversight. Basically I've exposed two new sysctls. /proc/sys/kernel/usermodehelper/bset /proc/sys/kernel/usermodehelper/inheritable You must have CAP_SYS_MODULE to change these (changes are &= ONLY). When the kernel launches a usermodehelper it will do so with these as the bset and pI. I haven't attempted securebits and uid (since I didn't really need them I don't think) But will if anyone can think of a use case. Is this what you were thinking? -Eric commit 23dbb6813349509a463103a34b51b18182c2ca0f Author: Eric Paris Date: Mon Feb 7 21:39:58 2011 -0500 limit kthreads usermode helper words stuff diff --git a/include/linux/kmod.h b/include/linux/kmod.h index 6efd7a7..79bb98d 100644 --- a/include/linux/kmod.h +++ b/include/linux/kmod.h @@ -24,6 +24,7 @@ #include #include #include +#include #define KMOD_PATH_LEN 256 @@ -109,6 +110,8 @@ call_usermodehelper(char *path, char **argv, char **envp, enum umh_wait wait) NULL, NULL, NULL); } +extern struct ctl_table usermodehelper_table[]; + extern void usermodehelper_init(void); extern int usermodehelper_disable(void); diff --git a/kernel/kmod.c b/kernel/kmod.c index 9cd0591..d38be14 100644 --- a/kernel/kmod.c +++ b/kernel/kmod.c @@ -25,6 +25,7 @@ #include #include #include +#include #include #include #include @@ -43,6 +44,12 @@ extern int max_threads; static struct workqueue_struct *khelper_wq; +#define CAP_BSET (void *)1 +#define CAP_PI (void *)2 + +kernel_cap_t usermodehelper_bset = CAP_FULL_SET; +kernel_cap_t usermodehelper_inheritable = CAP_FULL_SET; + #ifdef CONFIG_MODULES /* @@ -132,6 +139,8 @@ EXPORT_SYMBOL(__request_module); static int ____call_usermodehelper(void *data) { struct subprocess_info *sub_info = data; + const struct cred *old; + struct cred *new; int retval; spin_lock_irq(¤t->sighand->siglock); @@ -153,10 +162,23 @@ static int ____call_usermodehelper(void *data) goto fail; } + retval = -ENOMEM; + new = prepare_kernel_cred(current); + if (!new) + goto fail; + + new->cap_bset = usermodehelper_bset; + new->cap_inheritable = usermodehelper_inheritable; + + old = get_cred(current_cred()); + commit_creds(new); + retval = kernel_execve(sub_info->path, (const char *const *)sub_info->argv, (const char *const *)sub_info->envp); + commit_creds(old); + /* Exec failed? */ fail: sub_info->retval = retval; @@ -418,6 +440,79 @@ unlock: } EXPORT_SYMBOL(call_usermodehelper_exec); +static int proc_cap_handler(struct ctl_table *table, int write, + void __user *buffer, size_t *lenp, loff_t *ppos) +{ + struct ctl_table t; + unsigned long cap_array[_KERNEL_CAPABILITY_U32S]; + kernel_cap_t new_cap; + int err, i; + + if (write && !capable(CAP_SYS_MODULE)) + return -EPERM; + + /* + * convert from the global kernel_cap_t to the ulong array to print to + * userspace if this is a read. + */ + for (i = 0; i < _KERNEL_CAPABILITY_U32S; i++) { + if (table->data == CAP_BSET) + cap_array[i] = usermodehelper_bset.cap[i]; + else if (table->data == CAP_PI) + cap_array[i] = usermodehelper_inheritable.cap[i]; + else + BUG(); + } + + t = *table; + t.data = &cap_array; + + /* + * actually read or write and array of ulongs from userspace. Remember + * these are least significant 32 bits first + */ + err = proc_doulongvec_minmax(&t, write, buffer, lenp, ppos); + if (err < 0) + return err; + + /* + * convert from the sysctl array of ulongs to the kernel_cap_t + * internal representation + */ + for (i = 0; i < _KERNEL_CAPABILITY_U32S; i++) + new_cap.cap[i] = cap_array[i]; + + /* + * Drop everything not in the new_cap (but don't add things) + */ + if (write) { + if (table->data == CAP_BSET) + usermodehelper_bset = cap_intersect(usermodehelper_bset, new_cap); + if (table->data == CAP_PI) + usermodehelper_inheritable = cap_intersect(usermodehelper_inheritable, new_cap); + } + + return 0; +} + +struct ctl_table usermodehelper_table[] = { + { + .procname = "bset", + .data = CAP_BSET, + .maxlen = _KERNEL_CAPABILITY_U32S * sizeof(unsigned long), + .mode = 0600, + .proc_handler = proc_cap_handler, + }, + { + .procname = "inheritable", + .data = CAP_PI, + .maxlen = _KERNEL_CAPABILITY_U32S * sizeof(unsigned long), + .mode = 0600, + .proc_handler = proc_cap_handler, + }, + { } +}; + void __init usermodehelper_init(void) { khelper_wq = create_singlethread_workqueue("khelper"); diff --git a/kernel/sysctl.c b/kernel/sysctl.c index 0f1bd83..099d2e2 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -56,6 +56,7 @@ #include #include #include +#include #include #include @@ -617,6 +618,11 @@ static struct ctl_table kern_table[] = { .child = random_table, }, { + .procname = "usermodehelper", + .mode = 0555, + .child = usermodehelper_table, + }, + { .procname = "overflowuid", .data = &overflowuid, .maxlen = sizeof(int), -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/