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Subject[PATCH 7/9] syslog_ns: implement function for creating syslog ns
Date
Add create_syslog_ns function to create a new ns. We
must create a user_ns before create a new syslog ns.
And then tie the new syslog_ns to current user_ns
instead of original syslog_ns which comes from
parent user_ns.

Add a new syslog flag SYSLOG_ACTION_NEW_NS to implement
a new command(11) of __NR_syslog system call. Through
that command, we can create a new syslog ns in user
space.

Signed-off-by: Rui Xiang <rui.xiang@huawei.com>
---
include/linux/syslog.h | 2 ++
kernel/printk.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 54 insertions(+)

diff --git a/include/linux/syslog.h b/include/linux/syslog.h
index fbf0cb6..df57c21 100644
--- a/include/linux/syslog.h
+++ b/include/linux/syslog.h
@@ -46,6 +46,8 @@
#define SYSLOG_ACTION_SIZE_UNREAD 9
/* Return size of the log buffer */
#define SYSLOG_ACTION_SIZE_BUFFER 10
+/* Create a new syslog ns */
+#define SYSLOG_ACTION_NEW_NS 11

#define SYSLOG_FROM_READER 0
#define SYSLOG_FROM_PROC 1
diff --git a/kernel/printk.c b/kernel/printk.c
index fd2d600..6b561db 100644
--- a/kernel/printk.c
+++ b/kernel/printk.c
@@ -384,6 +384,10 @@ static int check_syslog_permissions(int type, bool from_file,
|| type == SYSLOG_ACTION_CONSOLE_LEVEL)
ns = &init_syslog_ns;

+ /* create a new syslog ns */
+ if (type == SYSLOG_ACTION_NEW_NS)
+ return 0;
+
if (syslog_action_restricted(type, ns)) {
if (ns_capable(ns->owner, CAP_SYSLOG))
return 0;
@@ -1131,6 +1135,51 @@ static int syslog_print_all(char __user *buf, int size, bool clear,
return len;
}

+static int create_syslog_ns(void)
+{
+ struct user_namespace *userns = current_user_ns();
+ struct syslog_namespace *oldns, *newns;
+ int err;
+
+ /*
+ * syslog ns belongs to a user ns. So you can only unshare your
+ * user_ns if you share a user_ns with your parent userns
+ */
+ if (userns == &init_user_ns ||
+ userns->syslog_ns != userns->parent->syslog_ns)
+ return -EINVAL;
+
+ if (!ns_capable(userns, CAP_SYSLOG))
+ return -EPERM;
+
+ err = -ENOMEM;
+ oldns = userns->syslog_ns;
+ newns = kzalloc(sizeof(*newns), GFP_ATOMIC);
+ if (!newns)
+ goto out;
+ newns->log_buf_len = __LOG_BUF_LEN;
+ newns->log_buf = kzalloc(newns->log_buf_len, GFP_ATOMIC);
+ if (!newns->log_buf)
+ goto out;
+
+ newns->owner = get_user_ns(userns);
+ raw_spin_lock_init(&(newns->logbuf_lock));
+ newns->logbuf_cpu = UINT_MAX;
+ newns->dmesg_restrict = oldns->dmesg_restrict;
+ put_syslog_ns(oldns);
+ kref_init(&newns->kref);
+ userns->syslog_ns = newns;
+ newns = NULL;
+
+ err = 0;
+out:
+ if (newns) {
+ kfree(newns->log_buf);
+ kfree(newns);
+ }
+ return err;
+}
+
int do_syslog(int type, char __user *buf, int len, bool from_file,
struct syslog_namespace *ns)
{
@@ -1254,6 +1303,9 @@ int do_syslog(int type, char __user *buf, int len, bool from_file,
case SYSLOG_ACTION_SIZE_BUFFER:
error = ns->log_buf_len;
break;
+ case SYSLOG_ACTION_NEW_NS:
+ error = create_syslog_ns();
+ break;
default:
error = -EINVAL;
break;
--
1.8.2.2



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