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* [PATCH] kernel: limit a value of ns_last_pid to (0, max_pid)
@ 2012-09-04  8:17 Andrew Vagin
  2012-09-04 16:04 ` Oleg Nesterov
  0 siblings, 1 reply; 2+ messages in thread
From: Andrew Vagin @ 2012-09-04  8:17 UTC (permalink / raw)
  To: Andrew Morton
  Cc: criu, linux-kernel, avagin, Andrew Morton, Oleg Nesterov,
	Eric W. Biederman, Pavel Emelyanov

The kernel doesn't check pid on a negative values, so if
you would try to write -2 in /proc/sys/kernel/ns_last_pid,
you will get a kernel panic.

In this case the next pid is -1, and alloc_pidmap will try to access
to a nonexistent pidmap.

map = &pid_ns->pidmap[pid/BITS_PER_PAGE];

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Pavel Emelyanov <xemul@parallels.com>
Acked-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Andrew Vagin <avagin@openvz.org>
---
 kernel/pid_namespace.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/kernel/pid_namespace.c b/kernel/pid_namespace.c
index b3c7fd5..6144bab 100644
--- a/kernel/pid_namespace.c
+++ b/kernel/pid_namespace.c
@@ -232,15 +232,19 @@ static int pid_ns_ctl_handler(struct ctl_table *table, int write,
 	 */
 
 	tmp.data = &current->nsproxy->pid_ns->last_pid;
-	return proc_dointvec(&tmp, write, buffer, lenp, ppos);
+	return proc_dointvec_minmax(&tmp, write, buffer, lenp, ppos);
 }
 
+extern int pid_max;
+static int zero = 0;
 static struct ctl_table pid_ns_ctl_table[] = {
 	{
 		.procname = "ns_last_pid",
 		.maxlen = sizeof(int),
 		.mode = 0666, /* permissions are checked in the handler */
 		.proc_handler = pid_ns_ctl_handler,
+		.extra1 = &zero,
+		.extra2 = &pid_max,
 	},
 	{ }
 };
-- 
1.7.1


^ permalink raw reply	[flat|nested] 2+ messages in thread

* Re: [PATCH] kernel: limit a value of ns_last_pid to (0, max_pid)
  2012-09-04  8:17 [PATCH] kernel: limit a value of ns_last_pid to (0, max_pid) Andrew Vagin
@ 2012-09-04 16:04 ` Oleg Nesterov
  0 siblings, 0 replies; 2+ messages in thread
From: Oleg Nesterov @ 2012-09-04 16:04 UTC (permalink / raw)
  To: Andrew Vagin
  Cc: Andrew Morton, criu, linux-kernel, Eric W. Biederman, Pavel Emelyanov

On 09/04, Andrew Vagin wrote:
>
> The kernel doesn't check pid on a negative values, so if
> you would try to write -2 in /proc/sys/kernel/ns_last_pid,
> you will get a kernel panic.
>
> In this case the next pid is -1, and alloc_pidmap will try to access
> to a nonexistent pidmap.
>
> map = &pid_ns->pidmap[pid/BITS_PER_PAGE];

Yes, alloc_pidmap() assumes that pid_ns->last_pid + 1 is positive...

So ".extra1 = &zero" is not enough, INT_MAX can overflow as well.

>  static struct ctl_table pid_ns_ctl_table[] = {
>  	{
>  		.procname = "ns_last_pid",
>  		.maxlen = sizeof(int),
>  		.mode = 0666, /* permissions are checked in the handler */
>  		.proc_handler = pid_ns_ctl_handler,
> +		.extra1 = &zero,
> +		.extra2 = &pid_max,

Acked-by: Oleg Nesterov <oleg@redhat.com>


^ permalink raw reply	[flat|nested] 2+ messages in thread

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