On 10/21/2015 10:12 PM, Kees Cook wrote:
On Wed, Oct 21, 2015 at 12:15 PM, Tycho Andersen
<tycho.ander...@canonical.com> wrote:
Hi Oleg,
On Wed, Oct 21, 2015 at 08:51:46PM +0200, Oleg Nesterov wrote:
On 10/20, Tycho Andersen wrote:
Hi Kees, Oleg,
On Tue, Oct 20, 2015 at 10:20:24PM +0200, Oleg Nesterov wrote:
No, you can't do copy_to_user() from atomic context. You need to pin this
filter, drop the lock/irq, then copy_to_user().
Attached is a patch which addresses this.
Looks good to me, feel free to add my reviewed-by.
a couple of questions, I am just curious...
+long seccomp_get_filter(struct task_struct *task, unsigned long filter_off,
+ void __user *data)
+{
+ struct seccomp_filter *filter;
+ struct sock_fprog_kern *fprog;
+ long ret;
+ unsigned long count = 0;
+
+ if (!capable(CAP_SYS_ADMIN) ||
+ current->seccomp.mode != SECCOMP_MODE_DISABLED) {
+ return -EACCES;
+ }
+
+ spin_lock_irq(&task->sighand->siglock);
+ if (task->seccomp.mode != SECCOMP_MODE_FILTER) {
+ ret = -EINVAL;
+ goto out;
+ }
+
+ filter = task->seccomp.filter;
+ while (filter) {
+ filter = filter->prev;
+ count++;
+ }
+
+ if (filter_off >= count) {
+ ret = -ENOENT;
+ goto out;
+ }
+ count -= filter_off;
+
+ filter = task->seccomp.filter;
+ while (filter && count > 1) {
+ filter = filter->prev;
+ count--;
+ }
+
+ if (WARN_ON(count != 1)) {
+ /* The filter tree shouldn't shrink while we're using it. */
+ ret = -ENOENT;
Yes. but this looks a bit confusing. If we want this WARN_ON() check
because we are paranoid, then we should do
WARN_ON(count != 1 || filter);
I guess you mean !filter here? We want filter to be non-null, because
we use it later.
And "while we're using it" look misleading, we rely on ->siglock.
Plus if we could be shrinked the additional check can't help anyway,
we can used the free filter. So I don't really understand this check
and "filter != NULL" in the previous "while (filter && count > 1)".
Nevermind...
Just paranoia. You're right that we could get rid of WARN_ON and the
null check. I can send an updated patch to drop these bits if
necessary. Kees?
I like being really paranoid when dealing with the filters. Let's keep
the WARN_ON (with the "|| !filter" added) but maybe wrap it in
"unlikely"?
Btw, the conditions inside the WARN_ON() macro would already resolve
to unlikely().
Best,
Daniel
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