linux-kernel - Re: [PATCH 1/2] bpf: Add BPF_MAP_TYPE_CRED

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <CAEXv5_griDfE03D1wDLH8chgCz0R2qZ5dAeiG0Rcg5sAicnMsg@mail.gmail.com>
Date: Sun, 14 Sep 2025 22:10:41 -0400
From: David Windsor <dwindsor@...il.com>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Song Liu <song@...nel.org>, bpf <bpf@...r.kernel.org>, 
	LKML <linux-kernel@...r.kernel.org>, Martin KaFai Lau <martin.lau@...ux.dev>, 
	Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
	Andrii Nakryiko <andrii@...nel.org>, Eduard <eddyz87@...il.com>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>
Subject: Re: [PATCH 1/2] bpf: Add BPF_MAP_TYPE_CRED_STORAGE map type and kfuncs

On Sun, Sep 14, 2025 at 9:10 PM Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
>
> On Sat, Sep 13, 2025 at 3:27 PM David Windsor <dwindsor@...il.com> wrote:
> >
> >
> >
> > On Sat, Sep 13, 2025 at 5:58 PM Song Liu <song@...nel.org> wrote:
> >>
> >> On Fri, Sep 12, 2025 at 5:27 PM David Windsor <dwindsor@...il.com> wrote:
> >> [...]
> >> > >
> >> > > Maybe I missed something, but I think you haven't addressed Alexei's
> >> > > question in v1: why this is needed and why hash map is not sufficient.
> >> > >
> >> > > Other local storage types (task, inode, sk storage) may get a large
> >> > > number of entries in a system, and thus would benefit from object
> >> > > local storage. I don't think we expect too many creds in a system.
> >> > > hash map of a smallish size should be good in most cases, and be
> >> > > faster than cred local storage.
> >> > >
> >> > > Did I get this right?
> >> > >
> >> > > Thanks,
> >> > > Song
> >> > >
> >> >
> >> > Yes I think I addressed in the cover letter of -v2:
> >> >
> >> > "Like other local storage types (task, inode, sk), this provides automatic
> >> > lifecycle management and is useful for LSM programs tracking credential
> >> > state across LSM calls. Lifetime management is necessary for detecting
> >> > credential leaks and enforcing time-based security policies."
> >> >
> >> > You're right it's faster and there aren't many creds, but I feel like
> >> > in this case, it'll be a nightmare to manual cleanup with hashmaps. I
> >> > think the correctness we get with lifetime management is worth it in
> >> > this case, but could be convinced otherwise. Many cred usage patterns
> >> > are short lived and a hash map could quickly become stale...
> >>
> >> We can clean up the hashmap in hook cred_free, no? The following
> >> check in security_cred_free() seems problematic:
> >>
> >>         if (unlikely(cred->security == NULL))
> >>                 return;
> >>
> >> But as far as I can tell, it is not really useful, and can be removed.
> >> With this removed, hash map will work just as well. Did I miss
> >> something?
> >
> >
> > No I think actually this is easier.
> >
> > I will prepare a patch for the race in cleanup I stumbled on earlier which is still there and could affect other users.
> >
> > That said, is there any use case for local storage for these structs:
> >
> > - struct file
> > - struct msg_msg
> > - struct ipc
> >
> > I can off the top of my head think of some security use cases for these but not sure if hashmaps are needed, perhaps struct file
>
> Sorry, no. This is not a copy paste territory.

no i get it's not copy/paste but I have the series for struct file
ready for submission, with selftests. this is also a performance
critical use case and there will be numerous struct file on edge
servers.

> The existing local storage maps were added because
> performance was critical for those use cases,
> but we made a few mistakes. There is a performance
> cliff that has to be fixed before we adopt it to
> other kernel objects.

ahh wasn't aware of this.

> Please use hash map and consider wrapping rhashtable
> as a new bpf map type if fixed max_entries is problematic.
>

makes sense thanks

> pw-bot: cr