On Fri, Aug 19, 2022 at 9:05 PM Christian Göttsche <cgzones@xxxxxxxxxxxxxx> wrote: > > On Wed, 22 Jun 2022 at 04:57, Aleksa Sarai <cyphar@xxxxxxxxxx> wrote: > > > > On 2022-06-20, Amir Goldstein <amir73il@xxxxxxxxx> wrote: > > > To be a reasonable reaction to the currently broken API is > > > to either accept the patch as is or request that setxattrat() > > > will be added to provide the new functionality. > > > > Since the current functionality cannot be retroactively disabled as it > > is being used already through /proc/self/fd/$n, adding > > *xattrat(AT_EMPTY_PATH) doesn't really change what is currently possible > > by userspace. > > > > I would say we should add *xattrat(2) and then we can add an upgrade > > mask blocking it (and other operations) later. > > > > It seems setxattrat() is the preferred way to continue. > fsetxattr() would have one advantage though (w.r.t. SELinux): > > The steps to label a file are: > 1. get the type of the file (via stat(2) family) > 2. lookup the desired label from the label database via selabel_lookup(3) > 3. assign the retrieved label to the file > > The label is sensitive to the file type, e.g. > > $ matchpathcon -m file /etc/shadow > /etc/shadow system_u:object_r:shadow_t:s0 > $ matchpathcon -m lnk_file /etc/shadow > /etc/shadow system_u:object_r:etc_t:s0 > > Using the *at() family the file type could change between step 1. and 3., > which operating on an O_PATH file descriptor would prevent. I don't understand the problem. If you have an O_PATH fd, the object it represents does not change. If you use fstatat(fd, ..., AT_EMPTY_PATH) (or fstat) and setxattrat(fd, ..., AT_EMPTY_PATH), it prevents the race. Thanks, Amir.
