[PATCH 2/3 v3] kernel/sysctl.c: threads-max observe limits

Heinrich Schuchardt
2015-02-21T22:20:08Z

Users can change the maximum number of threads by writing to
/proc/sys/kernel/threads-max.

With the patch the value entered is checked according to the same
limits that apply when fork_init is called.

Furthermore the limits of the init process are adjusted.
This will not update limits of any other existing processes.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
---
include/linux/sysctl.h | 3 +++
kernel/fork.c | 24 ++++++++++++++++++++++++
kernel/sysctl.c | 6 ++----
3 files changed, 29 insertions(+), 4 deletions(-)

diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
index b7361f8..795d5fe 100644
--- a/include/linux/sysctl.h
+++ b/include/linux/sysctl.h
@@ -212,4 +212,7 @@ static inline void setup_sysctl_set(struct ctl_table_set *p,

#endif /* CONFIG_SYSCTL */

+int sysctl_max_threads(struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp, loff_t *ppos);
+
#endif /* _LINUX_SYSCTL_H */
diff --git a/kernel/fork.c b/kernel/fork.c
index 69c30cd..38ffce5 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -74,6 +74,7 @@
#include <linux/uprobes.h>
#include <linux/aio.h>
#include <linux/compiler.h>
+#include <linux/sysctl.h>

#include <asm/pgtable.h>
#include <asm/pgalloc.h>
@@ -2024,3 +2025,26 @@ int unshare_files(struct files_struct **displaced)
task_unlock(task);
return 0;
}
+
+int sysctl_max_threads(struct ctl_table *table, int write,
+ void __user *buffer, size_t *lenp, loff_t *ppos)
+{
+ struct ctl_table t;
+ int ret;
+ int threads = max_threads;
+ int min = MIN_THREADS;
+ int max = MAX_THREADS;
+
+ t = *table;
+ t.data = &threads;
+ t.extra1 = &min;
+ t.extra2 = &max;
+
+ ret = proc_dointvec_minmax(&t, write, buffer, lenp, ppos);
+ if (ret || !write)
+ return ret;
+
+ set_max_threads(threads);
+
+ return 0;
+}
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 137c7f6..2e195ae 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -92,11 +92,9 @@
#include <linux/nmi.h>
#endif

-
#if defined(CONFIG_SYSCTL)

/* External variables not in a header file. */
-extern int max_threads;
extern int suid_dumpable;
#ifdef CONFIG_COREDUMP
extern int core_uses_pid;
@@ -709,10 +707,10 @@ static struct ctl_table kern_table[] = {
#endif
{
.procname = "threads-max",
- .data = &max_threads,
+ .data = NULL,
.maxlen = sizeof(int),
.mode = 0644,
- .proc_handler = proc_dointvec,
+ .proc_handler = sysctl_max_threads,
},
{
.procname = "random",
--
2.1.4