Re: [PATCH] fanotify: Make sure to check event_len when copying
From: Jan Kara
Date: Wed Dec 05 2018 - 07:10:41 EST
On Wed 05-12-18 09:15:44, Amir Goldstein wrote:
> On Wed, Dec 5, 2018 at 1:44 AM Kees Cook <keescook@xxxxxxxxxxxx> wrote:
> >
> > As a precaution, make sure we check event_len when copying to userspace.
> > Based on old feedback: https://lkml.kernel.org/r/542D9FE5.3010009@xxxxxx
> >
>
> This precaution serves the new fanotify_event_info_fid format well:
> https://marc.info/?l=linux-fsdevel&m=154375073318106&w=2
> but also conflicts with my series.
>
> I can weave your patch into my series and add a similar sanity check in
> copy_fid_to_user() or if Jan applies your patch and has more comments
> on my v4 series, I'll rebase on top of that.
Yeah, I don't think there's any need for you to rebase just now. Either
I'll fixup your patch or you'll do the rebase if there are further changes
to the series...
Honza
>
> Thanks,
> Amir.
>
> > Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>
> > ---
> > fs/notify/fanotify/fanotify_user.c | 10 ++++++++--
> > 1 file changed, 8 insertions(+), 2 deletions(-)
> >
> > diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
> > index e03be5071362..d9484a0ac6b3 100644
> > --- a/fs/notify/fanotify/fanotify_user.c
> > +++ b/fs/notify/fanotify/fanotify_user.c
> > @@ -206,7 +206,7 @@ static int process_access_response(struct fsnotify_group *group,
> >
> > static ssize_t copy_event_to_user(struct fsnotify_group *group,
> > struct fsnotify_event *event,
> > - char __user *buf)
> > + char __user *buf, size_t count)
> > {
> > struct fanotify_event_metadata fanotify_event_metadata;
> > struct file *f;
> > @@ -220,6 +220,12 @@ static ssize_t copy_event_to_user(struct fsnotify_group *group,
> >
> > fd = fanotify_event_metadata.fd;
> > ret = -EFAULT;
> > + /*
> > + * Sanity check copy size in case get_one_event() and
> > + * fill_event_metadata() event_len sizes ever get out of sync.
> > + */
> > + if (WARN_ON_ONCE(fanotify_event_metadata.event_len > count))
> > + goto out_close_fd;
> > if (copy_to_user(buf, &fanotify_event_metadata,
> > fanotify_event_metadata.event_len))
> > goto out_close_fd;
> > @@ -295,7 +301,7 @@ static ssize_t fanotify_read(struct file *file, char __user *buf,
> > continue;
> > }
> >
> > - ret = copy_event_to_user(group, kevent, buf);
> > + ret = copy_event_to_user(group, kevent, buf, count);
> > if (unlikely(ret == -EOPENSTALE)) {
> > /*
> > * We cannot report events with stale fd so drop it.
> > --
> > 2.17.1
> >
> >
> > --
> > Kees Cook
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR