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authorEric W. Biederman <ebiederm@xmission.com>2014-12-02 12:27:26 -0600
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2015-01-08 09:58:16 -0800
commit1c587ee50ec44a2cf07cd160c214a683608b4d2c (patch)
treeb6259344d064228a86830ae99a9c36fc89b71fca /fs
parent6eaab78729f4e689a86ce6bc4e33453ebff9625d (diff)
downloadlinux-linaro-stable-1c587ee50ec44a2cf07cd160c214a683608b4d2c.tar.gz
userns: Add a knob to disable setgroups on a per user namespace basis
commit 9cc46516ddf497ea16e8d7cb986ae03a0f6b92f8 upstream. - Expose the knob to user space through a proc file /proc/<pid>/setgroups A value of "deny" means the setgroups system call is disabled in the current processes user namespace and can not be enabled in the future in this user namespace. A value of "allow" means the segtoups system call is enabled. - Descendant user namespaces inherit the value of setgroups from their parents. - A proc file is used (instead of a sysctl) as sysctls currently do not allow checking the permissions at open time. - Writing to the proc file is restricted to before the gid_map for the user namespace is set. This ensures that disabling setgroups at a user namespace level will never remove the ability to call setgroups from a process that already has that ability. A process may opt in to the setgroups disable for itself by creating, entering and configuring a user namespace or by calling setns on an existing user namespace with setgroups disabled. Processes without privileges already can not call setgroups so this is a noop. Prodcess with privilege become processes without privilege when entering a user namespace and as with any other path to dropping privilege they would not have the ability to call setgroups. So this remains within the bounds of what is possible without a knob to disable setgroups permanently in a user namespace. Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'fs')
-rw-r--r--fs/proc/base.c53
1 files changed, 53 insertions, 0 deletions
diff --git a/fs/proc/base.c b/fs/proc/base.c
index de12b8128b95..8fc784aef0b8 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -2612,6 +2612,57 @@ static const struct file_operations proc_projid_map_operations = {
.llseek = seq_lseek,
.release = proc_id_map_release,
};
+
+static int proc_setgroups_open(struct inode *inode, struct file *file)
+{
+ struct user_namespace *ns = NULL;
+ struct task_struct *task;
+ int ret;
+
+ ret = -ESRCH;
+ task = get_proc_task(inode);
+ if (task) {
+ rcu_read_lock();
+ ns = get_user_ns(task_cred_xxx(task, user_ns));
+ rcu_read_unlock();
+ put_task_struct(task);
+ }
+ if (!ns)
+ goto err;
+
+ if (file->f_mode & FMODE_WRITE) {
+ ret = -EACCES;
+ if (!ns_capable(ns, CAP_SYS_ADMIN))
+ goto err_put_ns;
+ }
+
+ ret = single_open(file, &proc_setgroups_show, ns);
+ if (ret)
+ goto err_put_ns;
+
+ return 0;
+err_put_ns:
+ put_user_ns(ns);
+err:
+ return ret;
+}
+
+static int proc_setgroups_release(struct inode *inode, struct file *file)
+{
+ struct seq_file *seq = file->private_data;
+ struct user_namespace *ns = seq->private;
+ int ret = single_release(inode, file);
+ put_user_ns(ns);
+ return ret;
+}
+
+static const struct file_operations proc_setgroups_operations = {
+ .open = proc_setgroups_open,
+ .write = proc_setgroups_write,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = proc_setgroups_release,
+};
#endif /* CONFIG_USER_NS */
static int proc_pid_personality(struct seq_file *m, struct pid_namespace *ns,
@@ -2720,6 +2771,7 @@ static const struct pid_entry tgid_base_stuff[] = {
REG("uid_map", S_IRUGO|S_IWUSR, proc_uid_map_operations),
REG("gid_map", S_IRUGO|S_IWUSR, proc_gid_map_operations),
REG("projid_map", S_IRUGO|S_IWUSR, proc_projid_map_operations),
+ REG("setgroups", S_IRUGO|S_IWUSR, proc_setgroups_operations),
#endif
#ifdef CONFIG_CHECKPOINT_RESTORE
REG("timers", S_IRUGO, proc_timers_operations),
@@ -3073,6 +3125,7 @@ static const struct pid_entry tid_base_stuff[] = {
REG("uid_map", S_IRUGO|S_IWUSR, proc_uid_map_operations),
REG("gid_map", S_IRUGO|S_IWUSR, proc_gid_map_operations),
REG("projid_map", S_IRUGO|S_IWUSR, proc_projid_map_operations),
+ REG("setgroups", S_IRUGO|S_IWUSR, proc_setgroups_operations),
#endif
};