2.6.37-stable review patch. If anyone has any objections, please let us know.
------------------
From: Richard Weinberger <rich...@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 <rich...@nod.at>
Acked-by: Dan Rosenberg <drosenb...@vsecurity.com>
Acked-by: Serge E. Hallyn <se...@hallyn.com>
Cc: Eric Paris <epa...@redhat.com>
Cc: Kees Cook <kees.c...@canonical.com>
Cc: James Morris <jmor...@namei.org>
Cc: Eugene Teo <eugene...@kernel.org>
Signed-off-by: Andrew Morton <a...@linux-foundation.org>
Signed-off-by: Linus Torvalds <torva...@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gre...@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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