Re: [PATCH] Check files' signatures before doing suid/sgid [2/4]
From: Satyam Sharma <hidden>
Date: 2007-06-22 19:37:14
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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 [off-list ref] wrote:
sns_secret_key.dat contains the 'secret key' which is used for HMAC.
Where:
quoted hunk
--- /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