sysctl: restrict write access to dmesg_restrict

bfdc0b49 · Richard Weinberger <[email protected]> · 2011-03-23 16:43:11 -07:00

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 <[email protected]>
Acked-by: Dan Rosenberg <[email protected]>
Acked-by: Serge E. Hallyn <[email protected]>
Cc: Eric Paris <[email protected]>
Cc: Kees Cook <[email protected]>
Cc: James Morris <[email protected]>
Cc: Eugene Teo <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Commit: bfdc0b497faa82a0ba2f9dddcf109231dd519fcc
Parents: cb16e95f

Changes

1 files changed · +17 −1

File	Status	Add	Del	Content
kernel/sysctl.c	modified	+17	−1	View file

kernel/sysctl.c

View file

diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 97ab169..c0bb324 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -170,6 +170,11 @@ 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;
@@ -707,7 +712,7 @@ static struct ctl_table kern_table[] = {
 		.data		= &kptr_restrict,
 		.maxlen		= sizeof(int),
 		.mode		= 0644,
-		.proc_handler	= proc_dointvec_minmax,
+		.proc_handler	= proc_dmesg_restrict,
 		.extra1		= &zero,
 		.extra2		= &two,
 	},
@@ -2394,6 +2399,17 @@ 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;