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. 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
