[PATCH] pidhashing: enforce PID_MAX_LIMIT in sysctls

The pid_max sysctl doesn't enforce PID_MAX_LIMIT or sane lower bounds.
RESERVED_PIDS + 1 is the minimum pid_max that won't break alloc_pidmap(), and
PID_MAX_LIMIT may not be aligned to 8*PAGE_SIZE boundaries for unusual values
of PAGE_SIZE, so this also rounds up PID_MAX_LIMIT to it.
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

kernel/pid.c

@@ -36,7 +36,10 @@ int last_pid;
 
 #define RESERVED_PIDS		300
 
-#define PIDMAP_ENTRIES		(PID_MAX_LIMIT/PAGE_SIZE/8)
+int pid_max_min = RESERVED_PIDS + 1;
+int pid_max_max = PID_MAX_LIMIT;
+
+#define PIDMAP_ENTRIES		((PID_MAX_LIMIT + 8*PAGE_SIZE - 1)/PAGE_SIZE/8)
 #define BITS_PER_PAGE		(PAGE_SIZE*8)
 #define BITS_PER_PAGE_MASK	(BITS_PER_PAGE-1)
 #define mk_pid(map, off)	(((map) - pidmap_array)*BITS_PER_PAGE + (off))

kernel/sysctl.c

@@ -66,6 +66,7 @@ extern int sysctl_lower_zone_protection;
 extern int min_free_kbytes;
 extern int printk_ratelimit_jiffies;
 extern int printk_ratelimit_burst;
+extern int pid_max_min, pid_max_max;
 
 #if defined(CONFIG_X86_LOCAL_APIC) && defined(__i386__)
 int unknown_nmi_panic;
@@ -575,7 +576,10 @@ static ctl_table kern_table[] = {
 		.data		= &pid_max,
 		.maxlen		= sizeof (int),
 		.mode		= 0644,
-		.proc_handler	= &proc_dointvec,
+		.proc_handler	= &proc_dointvec_minmax,
+		.strategy	= sysctl_intvec,
+		.extra1		= &pid_max_min,
+		.extra2		= &pid_max_max,
 	},
 	{
 		.ctl_name	= KERN_PANIC_ON_OOPS,