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authorAdrian Reber <areber@redhat.com>2019-11-15 15:36:20 +0300
committerChristian Brauner <christian.brauner@ubuntu.com>2019-11-16 01:49:22 +0300
commit49cb2fc42ce4b7a656ee605e30c302efaa39c1a7 (patch)
tree74f53f8f9ccc4b49aa06416ca5e28c0ffb9097f5 /include/linux/pid_namespace.h
parent17a810699c189cb8f2f0ba21c7f83396599bea26 (diff)
downloadlinux-49cb2fc42ce4b7a656ee605e30c302efaa39c1a7.tar.xz
fork: extend clone3() to support setting a PID
The main motivation to add set_tid to clone3() is CRIU. To restore a process with the same PID/TID CRIU currently uses /proc/sys/kernel/ns_last_pid. It writes the desired (PID - 1) to ns_last_pid and then (quickly) does a clone(). This works most of the time, but it is racy. It is also slow as it requires multiple syscalls. Extending clone3() to support *set_tid makes it possible restore a process using CRIU without accessing /proc/sys/kernel/ns_last_pid and race free (as long as the desired PID/TID is available). This clone3() extension places the same restrictions (CAP_SYS_ADMIN) on clone3() with *set_tid as they are currently in place for ns_last_pid. The original version of this change was using a single value for set_tid. At the 2019 LPC, after presenting set_tid, it was, however, decided to change set_tid to an array to enable setting the PID of a process in multiple PID namespaces at the same time. If a process is created in a PID namespace it is possible to influence the PID inside and outside of the PID namespace. Details also in the corresponding selftest. To create a process with the following PIDs: PID NS level Requested PID 0 (host) 31496 1 42 2 1 For that example the two newly introduced parameters to struct clone_args (set_tid and set_tid_size) would need to be: set_tid[0] = 1; set_tid[1] = 42; set_tid[2] = 31496; set_tid_size = 3; If only the PIDs of the two innermost nested PID namespaces should be defined it would look like this: set_tid[0] = 1; set_tid[1] = 42; set_tid_size = 2; The PID of the newly created process would then be the next available free PID in the PID namespace level 0 (host) and 42 in the PID namespace at level 1 and the PID of the process in the innermost PID namespace would be 1. The set_tid array is used to specify the PID of a process starting from the innermost nested PID namespaces up to set_tid_size PID namespaces. set_tid_size cannot be larger then the current PID namespace level. Signed-off-by: Adrian Reber <areber@redhat.com> Reviewed-by: Christian Brauner <christian.brauner@ubuntu.com> Reviewed-by: Oleg Nesterov <oleg@redhat.com> Reviewed-by: Dmitry Safonov <0x7f454c46@gmail.com> Acked-by: Andrei Vagin <avagin@gmail.com> Link: https://lore.kernel.org/r/20191115123621.142252-1-areber@redhat.com Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Diffstat (limited to 'include/linux/pid_namespace.h')
-rw-r--r--include/linux/pid_namespace.h2
1 files changed, 2 insertions, 0 deletions
diff --git a/include/linux/pid_namespace.h b/include/linux/pid_namespace.h
index 49538b172483..2ed6af88794b 100644
--- a/include/linux/pid_namespace.h
+++ b/include/linux/pid_namespace.h
@@ -12,6 +12,8 @@
#include <linux/ns_common.h>
#include <linux/idr.h>
+/* MAX_PID_NS_LEVEL is needed for limiting size of 'struct pid' */
+#define MAX_PID_NS_LEVEL 32
struct fs_pin;