[PATCHv8 27/34] fs/proc: Introduce /proc/pid/timens_offsets

Dmitry Safonov
2019-11-12T01:27:16Z

From: Andrei Vagin <avagin@gmail.com>

API to set time namespace offsets for children processes, i.e.:
echo "clockid off_ses off_nsec" > /proc/self/timens_offsets

Signed-off-by: Andrei Vagin <avagin@gmail.com>
Co-developed-by: Dmitry Safonov <dima@arista.com>
Signed-off-by: Dmitry Safonov <dima@arista.com>
---
fs/proc/base.c | 95 +++++++++++++++++++++++++++++++
include/linux/time_namespace.h | 10 ++++
kernel/time/namespace.c | 100 +++++++++++++++++++++++++++++++++
3 files changed, 205 insertions(+)

diff --git a/fs/proc/base.c b/fs/proc/base.c
index ebea9501afb8..1d2007365e87 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -94,6 +94,7 @@
#include <linux/sched/debug.h>
#include <linux/sched/stat.h>
#include <linux/posix-timers.h>
+#include <linux/time_namespace.h>
#include <trace/events/oom.h>
#include "internal.h"
#include "fd.h"
@@ -1533,6 +1534,97 @@ static const struct file_operations proc_pid_sched_autogroup_operations = {

#endif /* CONFIG_SCHED_AUTOGROUP */

+#ifdef CONFIG_TIME_NS
+static int timens_offsets_show(struct seq_file *m, void *v)
+{
+ struct task_struct *p;
+
+ p = get_proc_task(file_inode(m->file));
+ if (!p)
+ return -ESRCH;
+ proc_timens_show_offsets(p, m);
+
+ put_task_struct(p);
+
+ return 0;
+}
+
+static ssize_t
+timens_offsets_write(struct file *file, const char __user *buf,
+ size_t count, loff_t *ppos)
+{
+ struct inode *inode = file_inode(file);
+ struct proc_timens_offset offsets[2];
+ char *kbuf = NULL, *pos, *next_line;
+ struct task_struct *p;
+ int ret, noffsets;
+
+ /* Only allow < page size writes at the beginning of the file */
+ if ((*ppos != 0) || (count >= PAGE_SIZE))
+ return -EINVAL;
+
+ /* Slurp in the user data */
+ kbuf = memdup_user_nul(buf, count);
+ if (IS_ERR(kbuf))
+ return PTR_ERR(kbuf);
+
+ /* Parse the user data */
+ ret = -EINVAL;
+ noffsets = 0;
+ for (pos = kbuf; pos; pos = next_line) {
+ struct proc_timens_offset *off = &offsets[noffsets];
+ int err;
+
+ /* Find the end of line and ensure we don't look past it */
+ next_line = strchr(pos, '\n');
+ if (next_line) {
+ *next_line = '\0';
+ next_line++;
+ if (*next_line == '\0')
+ next_line = NULL;
+ }
+
+ err = sscanf(pos, "%u %lld %lu", &off->clockid,
+ &off->val.tv_sec, &off->val.tv_nsec);
+ if (err != 3 || off->val.tv_nsec >= NSEC_PER_SEC)
+ goto out;
+ noffsets++;
+ if (noffsets == ARRAY_SIZE(offsets)) {
+ if (next_line)
+ count = next_line - kbuf;
+ break;
+ }
+ }
+
+ ret = -ESRCH;
+ p = get_proc_task(inode);
+ if (!p)
+ goto out;
+ ret = proc_timens_set_offset(file, p, offsets, noffsets);
+ put_task_struct(p);
+ if (ret)
+ goto out;
+
+ ret = count;
+out:
+ kfree(kbuf);
+ return ret;
+}
+
+static int timens_offsets_open(struct inode *inode, struct file *filp)
+{
+ return single_open(filp, timens_offsets_show, inode);
+}
+
+static const struct file_operations proc_timens_offsets_operations = {
+ .open = timens_offsets_open,
+ .read = seq_read,
+ .write = timens_offsets_write,
+ .llseek = seq_lseek,
+ .release = single_release,
+};
+#endif /* CONFIG_TIME_NS */
+
static ssize_t comm_write(struct file *file, const char __user *buf,
size_t count, loff_t *offset)
{
@@ -3015,6 +3107,9 @@ static const struct pid_entry tgid_base_stuff[] = {
#endif
#ifdef CONFIG_SCHED_AUTOGROUP
REG("autogroup", S_IRUGO|S_IWUSR, proc_pid_sched_autogroup_operations),
+#endif
+#ifdef CONFIG_TIME_NS
+ REG("timens_offsets", S_IRUGO|S_IWUSR, proc_timens_offsets_operations),
#endif
REG("comm", S_IRUGO|S_IWUSR, proc_pid_set_comm_operations),
#ifdef CONFIG_HAVE_ARCH_TRACEHOOK
diff --git a/include/linux/time_namespace.h b/include/linux/time_namespace.h
index f1cdd3a6f842..793d2486a87d 100644
--- a/include/linux/time_namespace.h
+++ b/include/linux/time_namespace.h
@@ -50,6 +50,16 @@ static inline void put_time_ns(struct time_namespace *ns)
kref_put(&ns->kref, free_time_ns);
}

+extern void proc_timens_show_offsets(struct task_struct *p, struct seq_file *m);
+
+struct proc_timens_offset {
+ int clockid;
+ struct timespec64 val;
+};
+
+extern int proc_timens_set_offset(struct file *file, struct task_struct *p,
+ struct proc_timens_offset *offsets, int n);
+
static inline void timens_add_monotonic(struct timespec64 *ts)
{
struct timens_offsets *ns_offsets = &current->nsproxy->time_ns->offsets;
diff --git a/kernel/time/namespace.c b/kernel/time/namespace.c
index 0dc0742ed1ee..267120f31699 100644
--- a/kernel/time/namespace.c
+++ b/kernel/time/namespace.c
@@ -8,6 +8,7 @@
#include <linux/user_namespace.h>
#include <linux/sched/signal.h>
#include <linux/sched/task.h>
+#include <linux/seq_file.h>
#include <linux/proc_ns.h>
#include <linux/export.h>
#include <linux/time.h>
@@ -333,6 +334,105 @@ static struct user_namespace *timens_owner(struct ns_common *ns)
return to_time_ns(ns)->user_ns;
}

+static void show_offset(struct seq_file *m, int clockid, struct timespec64 *ts)
+{
+ seq_printf(m, "%d %lld %ld\n", clockid, ts->tv_sec, ts->tv_nsec);
+}
+
+void proc_timens_show_offsets(struct task_struct *p, struct seq_file *m)
+{
+ struct ns_common *ns;
+ struct time_namespace *time_ns;
+
+ ns = timens_for_children_get(p);
+ if (!ns)
+ return;
+ time_ns = to_time_ns(ns);
+
+ show_offset(m, CLOCK_MONOTONIC, &time_ns->offsets.monotonic);
+ show_offset(m, CLOCK_BOOTTIME, &time_ns->offsets.boottime);
+ put_time_ns(time_ns);
+}
+
+int proc_timens_set_offset(struct file *file, struct task_struct *p,
+ struct proc_timens_offset *offsets, int noffsets)
+{
+ struct ns_common *ns;
+ struct time_namespace *time_ns;
+ struct timespec64 tp;
+ int i, err;
+
+ ns = timens_for_children_get(p);
+ if (!ns)
+ return -ESRCH;
+ time_ns = to_time_ns(ns);
+
+ if (!file_ns_capable(file, time_ns->user_ns, CAP_SYS_TIME)) {
+ put_time_ns(time_ns);
+ return -EPERM;
+ }
+
+ for (i = 0; i < noffsets; i++) {
+ struct proc_timens_offset *off = &offsets[i];
+
+ switch (off->clockid) {
+ case CLOCK_MONOTONIC:
+ ktime_get_ts64(&tp);
+ break;
+ case CLOCK_BOOTTIME:
+ ktime_get_boottime_ts64(&tp);
+ break;
+ default:
+ err = -EINVAL;
+ goto out;
+ }
+
+ err = -ERANGE;
+
+ if (off->val.tv_sec > KTIME_SEC_MAX || off->val.tv_sec < -KTIME_SEC_MAX)
+ goto out;
+
+ tp = timespec64_add(tp, off->val);
+ /*
+ * KTIME_SEC_MAX is divided by 2 to be sure that KTIME_MAX is
+ * still unreachable.
+ */
+ if (tp.tv_sec < 0 || tp.tv_sec > KTIME_SEC_MAX / 2)
+ goto out;
+ }
+
+ mutex_lock(&offset_lock);
+ if (time_ns->frozen_offsets) {
+ err = -EACCES;
+ goto out_unlock;
+ }
+
+ err = 0;
+ /* don't report errors after this line */
+ for (i = 0; i < noffsets; i++) {
+ struct proc_timens_offset *off = &offsets[i];
+ struct timespec64 *offset = NULL;
+
+ switch (off->clockid) {
+ case CLOCK_MONOTONIC:
+ offset = &time_ns->offsets.monotonic;
+ break;
+ case CLOCK_BOOTTIME:
+ offset = &time_ns->offsets.boottime;
+ break;
+ }
+
+ *offset = off->val;
+ }
+
+out_unlock:
+ mutex_unlock(&offset_lock);
+out:
+ put_time_ns(time_ns);
+
+ return err;
+}
+
const struct proc_ns_operations timens_operations = {
.name = "time",
.type = CLONE_NEWTIME,
--
2.24.0