Messages in this thread | | | Subject | Re: [PATCH] Restrict write access to dmesg_restrict | From | Dan Rosenberg <> | Date | Mon, 14 Mar 2011 15:49:55 -0400 |
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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 <drosenberg@vsecurity.com>
> > 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 <richard@nod.at> > --- > 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
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