lkml.org 
[lkml]   [2007]   [Jun]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH] Check files' signatures before doing suid/sgid [2/4]
    Hi Alexander, Johannes,

    [ Added linux-crypto to Cc: ]

    Wow, this is _one_ *intrusive* patchset indeed :-)

    But first: Have you checked the digsig project? It's been doing
    (for some time) what your current patchset proposes -- and
    it uses public key cryptosystems for the key management,
    which is decidedly better than using secret-keyed hashes
    (HMAC, XCBC). Also, digsig aims to protect executable
    binaries in general, and not just suid / sgid ones.

    Second: Can we have some discussion on the security model /
    threat model / trust model / cryptographic key management
    scheme of your signing mechanism? [I had read through the
    [0/4] mail you had sent yesterday, but found no relevant
    discussion on these aspects there.]

    From the patchset, it appears you use a *common* secret key
    for _all_ signed binaries, and it is set at kernel build-time itself:

    On 6/22/07, Alexander Wuerstlein <arw@arw.name> wrote:
    > sns_secret_key.dat contains the 'secret key' which is used for HMAC.

    Where:

    > --- /dev/null
    > +++ b/security/sns_secret_key.dat
    > +#define SNS_SECRET_KEY_SIZE 8
    > +static char sns_secret_key[SNS_SECRET_KEY_SIZE] =
    > + {
    > + 'd', 'e', 'a', 'd', 'b', 'e', 'e', 'f'
    > + };

    [ Ok, I won't nitpick as to why does this file look like a header,
    is #include-d in the C source as a header, but still has a .dat
    extension :-) ]

    Anyway, this is *totally* insecure and broken. Do you realize anybody
    who lays hands on the kernel image can now _trivially_ extract the
    should-have-been-a-secret key from it and use it to sign his own
    binaries?

    Satyam
    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2007-06-22 21:39    [W:0.023 / U:29.508 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site