Re: [PATCH 1/3] keys: add KEY_SPEC_DM_VERITY_KEYRING

[Andrew Halaney <andrew@amutable.com>]

On Thu, Oct 08, 2026 at 08:33:45PM +0300, Jarkko Sakkinen wrote:
> On Wed, Oct 07, 2026 at 10:30:14AM -0500, Andrew Halaney wrote:
> > On Fri, Sep 25, 2026 at 11:39:28AM +0300, Jarkko Sakkinen wrote:
> > > On Fri, Sep 18, 2026 at 02:59:49PM -0500, Andrew Halaney wrote:
> > > > On Fri, Sep 18, 2026 at 09:05:26AM +0100, David Howells wrote:
> > > > > Jarkko Sakkinen <jarkko@kernel.org> wrote:
> > > > > 
> > > > > > This is great for discussion but what we want for the commit message
> > > > > > is just motivation and resolution.
> > > > > 
> > > > > Actually, I think it's useful that Andrew wrote up the issues in the commit
> > > > > message - and I think it shows part of the motivation.  The 'writing a fake
> > > > > /proc/keys line in the description' is something I hadn't considered.
> > > > 
> > > > I'll defer to what you all want in the message here, I found it valuable
> > > > but I trend on the side of overly verbose admittedly!
> > > > 
> > > > > 
> > > > > > I don't think we need all this just to say that /proc/keys in a racy
> > > > > > query mechanism for production, which is an issue for dm-verity, given
> > > > > > that nothing else is available.
> > > > > 
> > > > > I think at some point, we will need a system call to search all for all
> > > > > accessible keys matching certain criteria by actually walking the key
> > > > > database.  The problem there is that there may be multiple hits, so we may
> > > > > need something like:
> > > > > 
> > > > > 	int count = find_key(key_serial_t start_id,
> > > > > 			     const char *type, const char *desc_prefix,
> > > > > 			     key_serial_t *results, size_t results_size,
> > > > > 			     unsigned int flags);
> > > > > 
> > > > > Allowing you to do:
> > > > > 
> > > > > 	key_serial_t dm_key;
> > > > > 	int n = find_key(0, "keyring", ".dm_verity", &dm_key, 1,
> > > > > 			 FIND_KEY_EXACT_DESC);
> > > > > 
> > > > > This wouldn't be as fast as a direct lookup since it would have to walk the
> > > > > key tree, doing name comparisons and perm checks on each key of the type.
> > > > > 
> > > > > > And secondly special keys are meant for implicit keyrings so isn't
> > > > > > that all there's to it?
> > > > > 
> > > > > I have no particular objection to setting aside a block of negative key IDs
> > > > > for special keyrings that need to be accessed a lot - though I would make
> > > > > common reg/unreg functions that take the ID to be registered and, say, set the
> > > > > block at -257..-512.  Moving the BFP keyring to -257 and DM to -258.
> > > > 
> > > > To be clear are you suggesting I do that for v2 here? Happy to make the
> > > > change and add some reuse to the registration functions, etc. I'm
> > > > guessing its fine to change the bpf id since its still only in -next?
> > > > 
> > > > The only awkward bit with making that more generic is that dm-verity
> > > > isn't __ro_after_init since its coming from a module possibly, and
> > > > because of the module usage I also protected it with a spinlock in case
> > > > someone's accessing it while you unload the module. Could just use one
> > > > spinlock for the whole generic array, and drop the __ro_after_init I
> > > > suppose.
> > > > 
> > > > Let me know if I'm not following properly!
> > > 
> > > I just read David's response and I think he made fair arguments,
> > > and patches look fine to me.
> > > 
> > > David, did you have anything? I could pick these.
> > > 
> > > Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
> > > 
> > 
> > Gentle ping :)
> 
> Understandable :-)
> 
> > 
> > Are we happy with these to get picked up?
> 
> Can you just do a resend that applies on top of latest mainline
> or my tree? I.e. b4 shazam was not happy about this.
> 
> Full log:
> 
> $ b4 shazam https://lore.kernel.org/keyrings/20260914-ajhalaney-dmverity-key-identifier-v1-2-01922dc1366a@amutable.com/
> Grabbing thread from lore.kernel.org/all/20260914-ajhalaney-dmverity-key-identifier-v1-2-01922dc1366a@amutable.com/t.mbox.gz
> 
> Breaking thread to remove parents of 20260914-ajhalaney-dmverity-key-identifier-v1-0-01922dc1366a@amutable.com
> Checking for newer revisions
> Grabbing search results from lore.kernel.org
> Analyzing 10 messages in the thread
> Analyzing 0 code-review messages
> Checking attestation on all messages, may take a moment...
> ---
>   ✗ [PATCH 1/3] keys: add KEY_SPEC_DM_VERITY_KEYRING
>     + Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org> (✓ DKIM/kernel.org)
>     + Reviewed-by: Christian Brauner (Amutable) <brauner@kernel.org> (✓ DKIM/kernel.org)
>   ✗ [PATCH 2/3] keys: add KEY_SPEC_FS_VERITY_KEYRING
>     + Reviewed-by: Christian Brauner (Amutable) <brauner@kernel.org> (✓ DKIM/kernel.org)
>   ✗ [PATCH 3/3] Documentation: keys: document IDs added since KEY_SPEC_REQKEY_AUTH_KEY
>     + Reviewed-by: Christian Brauner (Amutable) <brauner@kernel.org> (✓ DKIM/kernel.org)
>   ---
>   ✗ BADSIG: DKIM/amutable-com.20251104.gappssmtp.com
> ---
> Total patches: 3
> ---
>  Base: base-commit 1a1de54f7369cd2b5bac0f265910e60ad3a6b4c3 not known, ignoring
> Applying: keys: add KEY_SPEC_DM_VERITY_KEYRING
> Patch failed at 0001 keys: add KEY_SPEC_DM_VERITY_KEYRING
> error: patch failed: include/linux/key.h:441
> error: include/linux/key.h: patch does not apply
> error: patch failed: include/uapi/linux/keyctl.h:25
> error: include/uapi/linux/keyctl.h: patch does not apply
> error: patch failed: security/keys/process_keys.c:25
> error: security/keys/process_keys.c: patch does not apply
> hint: Use 'git am --show-current-patch=diff' to see the failed patch
> hint: When you have resolved this problem, run "git am --continue".
> hint: If you prefer to skip this patch, run "git am --skip" instead.
> hint: To restore the original branch and stop patching, run "git am --abort".
> hint: Disable this message with "git config advice.mergeConflict false"

Egh, sorry I was on linux-next. I'm also realizing that the
KEY_SPEC_BPF_KEYRING bit this sort of depends on is only in bpf-next
(i.e. 264d8fd2794f ("bpf, keys: Add a bpf keyring for program signature validation")).
Otherwise as is this conflicts on mainline and we'd just have to skip
the -9 the bpf keyring is using at the moment.

Should I just base on bpf-next that and send thru there instead? I can't recall
how kernel maintainers typically handle this other than cutting a stable
branch that both subsystems pull from, etc.

Thanks,
Andrew