Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755728Ab1CNTuB (ORCPT ); Mon, 14 Mar 2011 15:50:01 -0400 Received: from mx1.vsecurity.com ([209.67.252.12]:65207 "EHLO mx1.vsecurity.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753961Ab1CNTuA (ORCPT ); Mon, 14 Mar 2011 15:50:00 -0400 Subject: Re: [PATCH] Restrict write access to dmesg_restrict From: Dan Rosenberg To: Richard Weinberger Cc: akpm@linux-foundation.org, mingo@elte.hu, davem@davemloft.net, dzickus@redhat.com, randy.dunlap@oracle.com, linux-kernel@vger.kernel.org In-Reply-To: <1300131356-24389-1-git-send-email-richard@nod.at> References: <1300131356-24389-1-git-send-email-richard@nod.at> Content-Type: text/plain; charset="UTF-8" Date: Mon, 14 Mar 2011 15:49:55 -0400 Message-ID: <1300132195.2194.6.camel@dan> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2572 Lines: 78 On Mon, 2011-03-14 at 20:35 +0100, Richard Weinberger wrote: > When dmesg_restrict is set to 1 CAP_SYS_ADMIN is needed > to read the kernel ring buffer. > But a root user without CAP_SYS_ADMIN is able to reset > dmesg_restrict to 0. A minor correction, CAP_SYSLOG is needed to read the kernel syslog. But I think requiring CAP_SYS_ADMIN is appropriate to modify the value of the sysctl, so assuming the commit message reflects this: Acked-by: Dan Rosenberg > > This is an issue when e.g. LXC (Linux Containers) are used > and complete user space is running without CAP_SYS_ADMIN. > A unprivileged and jailed root user can bypass the > dmesg_restrict protection. > > With this patch writing to dmesg_restrict is only allowed > when root has CAP_SYS_ADMIN. > > Signed-off-by: Richard Weinberger > --- > kernel/sysctl.c | 18 +++++++++++++++++- > 1 files changed, 17 insertions(+), 1 deletions(-) > > diff --git a/kernel/sysctl.c b/kernel/sysctl.c > index 4eed0af..f90c8f6 100644 > --- a/kernel/sysctl.c > +++ b/kernel/sysctl.c > @@ -169,6 +169,11 @@ static int proc_taint(struct ctl_table *table, int write, > void __user *buffer, size_t *lenp, loff_t *ppos); > #endif > > +#ifdef CONFIG_PRINTK > +static int proc_dmesg_restrict(struct ctl_table *table, int write, > + void __user *buffer, size_t *lenp, loff_t *ppos); > +#endif > + > #ifdef CONFIG_MAGIC_SYSRQ > /* Note: sysrq code uses it's own private copy */ > static int __sysrq_enabled = SYSRQ_DEFAULT_ENABLE; > @@ -704,7 +709,7 @@ static struct ctl_table kern_table[] = { > .data = &dmesg_restrict, > .maxlen = sizeof(int), > .mode = 0644, > - .proc_handler = proc_dointvec_minmax, > + .proc_handler = proc_dmesg_restrict, > .extra1 = &zero, > .extra2 = &one, > }, > @@ -2397,6 +2402,17 @@ static int proc_taint(struct ctl_table *table, int write, > return err; > } > > +#ifdef CONFIG_PRINTK > +static int proc_dmesg_restrict(struct ctl_table *table, int write, > + void __user *buffer, size_t *lenp, loff_t *ppos) > +{ > + if (write && !capable(CAP_SYS_ADMIN)) > + return -EPERM; > + > + return proc_dointvec_minmax(table, write, buffer, lenp, ppos); > +} > +#endif > + > struct do_proc_dointvec_minmax_conv_param { > int *min; > int *max; > -- > 1.6.6.1 -- 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/