On Fri, Aug 09, 2024 at 02:06:56PM +0200, Christian Brauner wrote: > On Thu, Aug 08, 2024 at 03:27:11PM GMT, Josef Bacik wrote: > > From: Amir Goldstein <[email protected]> > > > > With FAN_DENY response, user trying to perform the filesystem operation > > gets an error with errno set to EPERM. > > > > It is useful for hierarchical storage management (HSM) service to be able > > to deny access for reasons more diverse than EPERM, for example EAGAIN, > > if HSM could retry the operation later. > > > > Allow fanotify groups with priority FAN_CLASSS_PRE_CONTENT to responsd > > to permission events with the response value FAN_DENY_ERRNO(errno), > > instead of FAN_DENY to return a custom error. > > > > Limit custom error values to errors expected on read(2)/write(2) and > > open(2) of regular files. This list could be extended in the future. > > Userspace can test for legitimate values of FAN_DENY_ERRNO(errno) by > > writing a response to an fanotify group fd with a value of FAN_NOFD in > > the fd field of the response. > > > > The change in fanotify_response is backward compatible, because errno is > > written in the high 8 bits of the 32bit response field and old kernels > > reject respose value with high bits set. > > > > Signed-off-by: Amir Goldstein <[email protected]> > > --- > > fs/notify/fanotify/fanotify.c | 18 ++++++++++----- > > fs/notify/fanotify/fanotify.h | 10 +++++++++ > > fs/notify/fanotify/fanotify_user.c | 36 +++++++++++++++++++++++++----- > > include/linux/fanotify.h | 5 ++++- > > include/uapi/linux/fanotify.h | 7 ++++++ > > 5 files changed, 65 insertions(+), 11 deletions(-) > > > > diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c > > index 4e8dce39fa8f..1cbf41b34080 100644 > > --- a/fs/notify/fanotify/fanotify.c > > +++ b/fs/notify/fanotify/fanotify.c > > @@ -224,7 +224,8 @@ static int fanotify_get_response(struct fsnotify_group > > *group, > > struct fanotify_perm_event *event, > > struct fsnotify_iter_info *iter_info) > > { > > - int ret; > > + int ret, errno; > > + u32 decision; > > > > pr_debug("%s: group=%p event=%p\n", __func__, group, event); > > > > @@ -257,20 +258,27 @@ static int fanotify_get_response(struct > > fsnotify_group *group, > > goto out; > > } > > > > + decision = fanotify_get_response_decision(event->response); > > /* userspace responded, convert to something usable */ > > - switch (event->response & FANOTIFY_RESPONSE_ACCESS) { > > + switch (decision & FANOTIFY_RESPONSE_ACCESS) { > > case FAN_ALLOW: > > ret = 0; > > break; > > case FAN_DENY: > > + /* Check custom errno from pre-content events */ > > + errno = fanotify_get_response_errno(event->response); > > Fwiw, you're fetching from event->response again but have already > stashed it in @decision earlier. Probably just an oversight. >
Decision is the part that has the errno masked off, event->response is the full mask which will have the errno set in the upper bits, so we have to do the separate call with event->response to get the errno. Thanks, Josef
