From: David Windsor <dwindsor@gmail.com>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net,
andrii@kernel.org, martin.lau@linux.dev, song@kernel.org,
kpsingh@kernel.org, john.fastabend@gmail.com,
brauner@kernel.org, jack@suse.cz, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH bpf-next 1/2] bpf: Add dentry kfuncs for BPF LSM programs
Date: Wed, 24 Sep 2025 20:56:08 -0400 [thread overview]
Message-ID: <CAEXv5_hD_4ON3MVBa7+gpapQs+Vkvo6Ln+BKT+Qz_S7x+Up6hg@mail.gmail.com> (raw)
In-Reply-To: <20250925004725.GY39973@ZenIV>
On Wed, Sep 24, 2025 at 8:47 PM Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> On Wed, Sep 24, 2025 at 08:44:24PM -0400, David Windsor wrote:
>
> > > You can safely clone and retain file references. You can't do that
> > > to dentries unless you are guaranteed an active reference to superblock
> > > to stay around for as long as you are retaining those. Note that
> > > LSM hooks might be called with ->s_umount held by caller, so the locking
> > > environment for superblocks depends upon the hook in question.
> >
> > Yeah good point about ->s_umount, why don't we just create a new "safe
> > dentry hooks" BTF ID set and restrict this to those and filter in
> > bpf_fs_kfuncs_filter, where there's existing filtering going on
> > anyway?
>
> Again, you can't just call dget(), stash the reference into a map and move
> on. That's asking for UAF.
These can't be stored in a map (guaranteed by verifier during addr leak checks)
next prev parent reply other threads:[~2025-09-25 0:56 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-09-24 23:24 [PATCH bpf-next 0/2] bpf: Add more dentry kfuncs for BPF LSM programs David Windsor
2025-09-24 23:24 ` [PATCH bpf-next 1/2] bpf: Add " David Windsor
2025-09-24 23:55 ` Al Viro
2025-09-25 0:08 ` David Windsor
2025-09-25 0:29 ` Al Viro
2025-09-25 0:44 ` David Windsor
2025-09-25 0:47 ` Al Viro
2025-09-25 0:56 ` David Windsor [this message]
2025-09-29 8:24 ` Christian Brauner
2025-09-24 23:24 ` [PATCH bpf-next 2/2] selftests/bpf: Add tests for dentry kfuncs David Windsor
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