Messages in this thread Patch in this message | | | Date | Fri, 25 Mar 2011 16:47:16 -0700 | From | Greg KH <> | Subject | [23/55] sysctl: restrict write access to dmesg_restrict |
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2.6.37-stable review patch. If anyone has any objections, please let us know.
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From: Richard Weinberger <richard@nod.at>
commit bfdc0b497faa82a0ba2f9dddcf109231dd519fcc upstream.
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.
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> Acked-by: Dan Rosenberg <drosenberg@vsecurity.com> Acked-by: Serge E. Hallyn <serge@hallyn.com> Cc: Eric Paris <eparis@redhat.com> Cc: Kees Cook <kees.cook@canonical.com> Cc: James Morris <jmorris@namei.org> Cc: Eugene Teo <eugeneteo@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
--- kernel/sysctl.c | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-)
--- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -168,6 +168,11 @@ static int proc_taint(struct ctl_table * 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; @@ -1469,7 +1474,7 @@ static struct ctl_table fs_table[] = { .data = &suid_dumpable, .maxlen = sizeof(int), .mode = 0644, - .proc_handler = proc_dointvec_minmax, + .proc_handler = proc_dmesg_restrict, .extra1 = &zero, .extra2 = &two, }, @@ -2400,6 +2405,17 @@ static int proc_taint(struct ctl_table * 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;
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