Re: [PATCH 0/4] vfs: if RESOLVE_NO_XDEV passed to openat2, don't *trigger* automounts

On 2025-08-17, Askar Safin <[email protected]> wrote:
> openat2 had a bug: if we pass RESOLVE_NO_XDEV, then openat2
> doesn't traverse through automounts, but may still trigger them.
> See this link for full bug report with reproducer:
> https://lore.kernel.org/linux-fsdevel/[email protected]/
> 
> This patchset fixes the bug.
> 
> RESOLVE_NO_XDEV logic hopefully becomes more clear:
> now we immediately fail when we cross mountpoints.
> 
> I think this patchset should get to -fixes and stable trees.

You need to add

  Cc: <[email protected]> # v5.2+

(along with a Fixes: ... tag) for each commit you would like to be
backported.

> I split everything to very small commits to make
> everything as bisectable as possible.

I would merge the first three patches -- adding and removing code like
that is a little unnecessary. I also don't think you need those patches
to be backported, right? (Especially since they are touching stuff that
Al has reworked a few times since openat2 was merged back in Linux 5.2.)

I only think the last one needs to be in stable.

> Minimal testing was performed. I tested that my original
> reproducer doesn't reproduce anymore. And I did boot-test
> with localmodconfig in qemu
> 
> I'm not very attached to this patchset. I. e. I will not be offended
> if someone else will submit different fix for this bug.
> 
> Askar Safin (4):
>   vfs: fs/namei.c: move cross-device check to traverse_mounts
>   vfs: fs/namei.c: remove LOOKUP_NO_XDEV check from handle_mounts
>   vfs: fs/namei.c: move cross-device check to __traverse_mounts

This is a minor nit, but could you use something like "namei: ..." (or
"fs: namei: ...") as a prefix for commit subjects? If you merge them
all, something like:

  namei: move LOOKUP_NO_XDEV checks to __traverse_mounts

would be fine.

>   vfs: fs/namei.c: if RESOLVE_NO_XDEV passed to openat2, don't *trigger*
>     automounts

and this one should read a bit clearer with

  openat2: don't trigger automounts with RESOLVE_NO_XDEV

or if you prefer

  namei: don't trigger automounts with LOOKUP_NO_XDEV

>  fs/namei.c | 29 +++++++++++++++++++++++------
>  1 file changed, 23 insertions(+), 6 deletions(-)

-- 
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
https://www.cyphar.com/

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