Re: [Linux-ima-user] evmctl ima_sign + ima_verify failure

[Mimi Z. <zo...@li...>]

On Fri, 2015-07-10 at 22:14 +0200, Patrick Ohly wrote:
> On Fri, 2015-07-10 at 15:51 -0400, Mimi Zohar wrote:
> > On Fri, 2015-07-10 at 15:46 +0200, Patrick Ohly wrote:
> > > Hello!
> > > 
> > > I have (at least) one file where verifying the signature created by
> > > evmctl ima_sign fails. ima-evm-utils is 0.9 (git rev 3d9bdc1de2, the
> > > current master).
> > 
> > Was the file previously signed before this?   In enforcing mode,
> > existing signatures are considered to be "immutable" and can not be
> > removed/replaced.
> 
> I'm running these commands on a build host which does not have IMA
> enabled. So it's really a test of the code inside evmctl. It seems to
> produce a bad security.ima; both the kernel (on a different system) and
> evmctl's own signature check code agree on that.

Weird!  evmctl has support for signing hashes.  Create a sha256sums (eg.
sha256sum  <filename> > ./sha256sums.)   Then sign the hash(es) in the
sha256sums file.  

eg.  cat ./sha256sums | evmctl sign_hash -a sha256 --key "${PRIVKEY}" > sha256sums.sig

Compare the resulting signature in the sha256sums.sig file with the
extended attribute.  If the file hasn't changed, then they should be the
same.

> > > $ evmctl ima_sign privkey_ima.pem pam_securetty.so
> > > $ getfattr -d -m . pam_securetty.so 
> > > getfattr: Removing leading '/' from absolute path names
> > > # file: tmp/pam_securetty.so
> > > security.ima=0sAwIC2C1O/QCAEQNetDHu9W+Zn5bpL+cC2BvdkJNs6GIkS5EmD75MXrk+K0e0GLZOmAqwLbe/jOnsnw00WbthqG5xo7Vop+yDGnNVlGU95YQ1KQEqC3OZILkF5gyY88AU/T3y6UGa5Vl1FEvUrp4aVOUmTwqO6Wm/bVtJnNilhxkvRItjVNcVgQ==
> > > $ evmctl ima_verify --key x509_ima.der pam_securetty.so 
> > > RSA_public_decrypt() failed: -1
> > > error:0407006A:rsa routines:RSA_padding_check_PKCS1_type_1:block type is not 01
> > > error:04067072:rsa routines:RSA_EAY_PUBLIC_DECRYPT:padding check failed
> > 
> > When displaying security.ima, please use the "-e hex" option. 
> 
> Then I get:
> security.ima=0x030202d82d4efd008011035eb431eef56f999f96e92fe702d81bdd90936ce862244b91260fbe4c5eb93e2b47b418b64e980ab02db7bf8ce9ec9f0d3459bb61a86e71a3b568a7ec831a735594653de5843529012a0b739920b905e60c98f3c014fd3df2e9419ae55975144bd4ae9e1a54e5264f0a8ee969bf6d5b499cd8a587192f448b6354d71581
> 
> > > The signature check done by the Linux kernel 3.19.2 also fails.
> > 
> > Compare the key embedded in the signature with the key on the IMA
> > keyring.  For example, /bin/more on my system is signed with the pseudo
> > fedora signing key - 0x96042912.   (The keyid are the last bytes of the
> > key.)
> 
> In this case, I specify the keys explicitly (privkey_ima.pem and
> x509_ima.der). I know that they match, because signing some other file
> and verifying it works.

Please list the public keys loaded on the IMA keyring that are used to
verify the signature.

Mimi