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Subject[PATCH] pid: restore the old behaviour of the ns_last_pid sysctl
Date
CRIU uses ns_last_pid to fork a process with a specified pid. For
example, if we need to create a process with the pid of 10000,
we write 9999 into /proc/sys/kernel/ns_last_pid

$ echo 9999 > /proc/sys/kernel/ns_last_pid; sh -c 'echo $$'
10000

This behaviour has been broken and now if we write 9999 to ns_last_pid,
a process will get the pid 9999. This patch restores the old behaviour.

fixes: ("pid: replace pid bitmap implementation with IDR API")
Cc: Gargi Sharma <gs051095@gmail.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrei Vagin <avagin@openvz.org>
---
kernel/pid_namespace.c | 15 +++++++++++++--
1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index fea2c24fa460..504dadb1d920 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -287,6 +287,7 @@ static int pid_ns_ctl_handler(struct ctl_table *table, int write,
{
struct pid_namespace *pid_ns = task_active_pid_ns(current);
struct ctl_table tmp = *table;
+ int ret, next;

if (write && !ns_capable(pid_ns->user_ns, CAP_SYS_ADMIN))
return -EPERM;
@@ -297,8 +298,18 @@ static int pid_ns_ctl_handler(struct ctl_table *table, int write,
* it should synchronize its usage with external means.
*/

- tmp.data = &pid_ns->idr.idr_next;
- return proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
+ next = idr_get_cursor(&pid_ns->idr) - 1;
+
+ tmp.data = &next;
+ ret = proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
+ if (ret < 0)
+ return ret;
+
+ if (!write)
+ return 0;
+
+ idr_set_cursor(&pid_ns->idr, next + 1);
+ return 0;
}

extern int pid_max;
--
2.13.6
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