On Wed Sep 25, 2024 at 12:59 AM EEST, Eric Biggers wrote:
> On Wed, Sep 25, 2024 at 12:36:01AM +0300, Jarkko Sakkinen wrote:
> > On Tue Sep 24, 2024 at 9:27 PM EEST, Mikulas Patocka wrote:
> > >
> > >
> > > On Tue, 24 Sep 2024, Jarkko Sakkinen wrote:
> > >
> > > > On Mon Sep 23, 2024 at 5:04 PM EEST, Mikulas Patocka wrote:
> > > > >
> > > > >
> > > > > On Sun, 22 Sep 2024, luca.bocca...@gmail.com wrote:
> > > > >
> > > > > > From: Luca Boccassi <bl...@debian.org>
> > > > > > 
> > > > > > If enabled, we fallback to the platform keyring if the trusted 
> > > > > > keyring doesn't have
> > > > > > the key used to sign the roothash. But if pkcs7_verify() rejects 
> > > > > > the key for other
> > > > > > reasons, such as usage restrictions, we do not fallback. Do so.
> > > > > > 
> > > > > > Follow-up for 6fce1f40e95182ebbfe1ee3096b8fc0b37903269
> > > > > > 
> > > > > > Suggested-by: Serge Hallyn <se...@hallyn.com>
> > > > > > Signed-off-by: Luca Boccassi <bl...@debian.org>
> > > > >
> > > > > Hi
> > > > >
> > > > > I'm not an expert in keyrings.
> > > > >
> > > > > I added keyring maintainers to the CC. Please review this patch and 
> > > > > Ack/Nack it.
> > > > >
> > > > > Mikulas
> > > > >
> > > > > > ---
> > > > > >  drivers/md/dm-verity-verify-sig.c | 2 +-
> > > > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > > > 
> > > > > > diff --git a/drivers/md/dm-verity-verify-sig.c 
> > > > > > b/drivers/md/dm-verity-verify-sig.c
> > > > > > index d351d7d39c60..a9e2c6c0a33c 100644
> > > > > > --- a/drivers/md/dm-verity-verify-sig.c
> > > > > > +++ b/drivers/md/dm-verity-verify-sig.c
> > > > > > @@ -127,7 +127,7 @@ int verity_verify_root_hash(const void 
> > > > > > *root_hash, size_t root_hash_len,
> > > > > >  #endif
> > > > > >                             VERIFYING_UNSPECIFIED_SIGNATURE, NULL, 
> > > > > > NULL);
> > > > > >  #ifdef CONFIG_DM_VERITY_VERIFY_ROOTHASH_SIG_PLATFORM_KEYRING
> > > > > > -   if (ret == -ENOKEY)
> > > > > > +   if (ret == -ENOKEY || ret == -EKEYREJECTED)
> > > > > >             ret = verify_pkcs7_signature(root_hash, root_hash_len, 
> > > > > > sig_data,
> > > > > >                                     sig_len,
> > > > > >                                     VERIFY_USE_PLATFORM_KEYRING,
> > > > > > -- 
> > > > > > 2.39.5
> > > > > > 
> > > > 
> > > > I know nothing about dm-verity. What does it even do?
> > > > 
> > > > BR, Jarkko
> > >
> > > dm-verity provides a read-only device with integrity checking. dm-verity 
> > > stores hash for every block on the block device and checks the hash when 
> > > reading the block. If the hash doesn't match, it can do one of these 
> > > actions (depending on configuration):
> > > - return I/O error
> > > - try to correct the data using forward error correction
> > > - log the mismatch and do nothing
> > > - restart the machine
> > > - call panic()
> > >
> > > dm-verity is mostly used for the immutable system partition on Android 
> > > phones. For more info, see 
> > > Documentation/admin-guide/device-mapper/verity.rst
> > >
> > > The above patch changes the way that the signature of the root hash is 
> > > verified. I have no clue whether the patch can or can't subvert system 
> > > security, that's why I'd like to have some more reviews of the patch 
> > > before accepting it.
> > 
> > I guess someone who knows all this already should review it.
> > 
> > Doesn't dm-verity have a maintainer?
> > 
>
> This patch only affects dm-verity's in-kernel signature verification support,
> which has only been present since Linux v5.4 and is not used by Android or
> Chrome OS.  The whole feature seems weird to me, and it is prone to be 
> misused;
> signatures are best verified by trusted userspace code instead (e.g. 
> initramfs).
> But apparently there are people who use the dm-verity in-kernel signatures.  I
> think systemd has some support for it, as does the recently-upstreamed IPE 
> LSM.
> I don't know what else.  The exact semantics of the "trusted" and "platform"
> keyrings are not entirely clear to me, but given that dm-verity already trusts
> keys from both keyrings this patch seems reasonable.  The people who actually
> use this feature are in the best position to make that call, though.

https://lwn.net/Articles/459420/

Isn't Netflix using FreeBSD these days? :-)

Right, and Chromebooks also mentioned in the same article (from 2011).

For me this looks almost like abaddonware...

>
> - Eric

BR, Jarkko

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