> On Jul 4, 2025, at 2:00 AM, Mickaël Salaün <mic@xxxxxxxxxxx> wrote: > > On Thu, Jul 03, 2025 at 10:27:02PM +0000, Song Liu wrote: >> Hi Mickaël, >> >>> On Jul 3, 2025, at 11:29 AM, Mickaël Salaün <mic@xxxxxxxxxxx> wrote: >>> >>> On Mon, Jun 16, 2025 at 11:11:13PM -0700, Song Liu wrote: >>>> Use path_walk_parent() to walk a path up to its parent. >>>> >>>> No functional changes intended. >>> >>> Using this helper actualy fixes the issue highlighted by Al. Even if it >>> was reported after the first version of this patch series, the issue >>> should be explained in the commit message and these tags should be >>> added: >>> >>> Reported-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx> >>> Closes: https://lore.kernel.org/r/20250529231018.GP2023217@ZenIV >>> Fixes: cb2c7d1a1776 ("landlock: Support filesystem access-control") >>> >>> I like this new helper but we should have a clear plan to be able to >>> call such helper in a RCU read-side critical section before we merge >>> this series. We're still waiting for Christian. >>> >>> I sent a patch to fix the handling of disconnected directories for >>> Landlock, and it will need to be backported: >>> https://lore.kernel.org/all/20250701183812.3201231-1-mic@xxxxxxxxxxx/ >>> Unfortunately a rebase would be needed for the path_walk_parent patch, >>> but I can take it in my tree if everyone is OK. >> >> The fix above also touches VFS code (makes path_connected available >> out of namei.c. It probably should also go through VFS tree? >> >> Maybe you can send 1/5 and 2/5 of this set (with necessary changes) >> and your fix together to VFS tree. Then, I will see how to route the >> BPF side patches. > > That could work, but because it would be much more Landlock-specific > code than VFS-specific code, and there will probably be a few versions > of my fixes, I'd prefer to keep this into my tree if VFS folks are OK. > BTW, my fixes already touch the VFS subsystem a bit. > > However, as pointed out in my previous email, the disconnected directory > case should be carefully considered for the path_walk_parent() users to > avoid BPF LSM programs having the same issue I'm fixing for Landlock. > The safe approaches I can think of to avoid this issue for BPF programs > while making the interface efficient (by not calling path_connected() > after each path_walk_parent() call) is to either have some kind of > iterator as Tingmao proposed, or a callback function as Neil proposed. > The callback approach looks simpler and more future-proof, but I guess > you'll have to make it compatible with the eBPF runtime. I think the > best approach would be to have a VFS API with a callback, and a BPF > helper (leveraging this VFS API) with an iterator state. Since we are proposing an open-coded BPF iterator. Having a real callback, which is no longer an open coded iterator, requires more work. At the moment, it is easier to just add a path_connected call in bpf_iter_path_next(). Thanks, Song
