From: Al Viro <viro@zeniv.linux.org.uk>
To: David Windsor <dwindsor@gmail.com>
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: Thu, 25 Sep 2025 01:47:25 +0100 [thread overview]
Message-ID: <20250925004725.GY39973@ZenIV> (raw)
In-Reply-To: <CAEXv5_hEXggxe5EwSHV8SK21e6HNmfYFSE9kx=ojwEobtTTGLA@mail.gmail.com>
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.
next prev parent reply other threads:[~2025-09-25 0:47 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 [this message]
2025-09-25 0:56 ` David Windsor
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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