Messages in this thread | | | Subject | Re: [Linux-ima-devel] [PATCH 0/7] IMA: new parser for ima_restore_measurement_list() | From | Ken Goldman <> | Date | Tue, 23 May 2017 16:48:44 -0400 |
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On 5/18/2017 5:38 AM, Roberto Sassu wrote: > On 5/17/2017 6:28 PM, Ken Goldman wrote: >> On 5/17/2017 3:25 AM, Roberto Sassu wrote: >>> >>> The format of digestN is: <algo name>:\0<digest value>, the same used >>> for the file digest. >> >> Since the format is changing from the SHA-1 log format anyway ... >> >> How do people feel about the colon and null terminated string format for >> algorithm identifiers? >> >> The TCG standard enumerations are uint16_t, and there is a registry of >> hash algorithms. >> >> As a consuming parser, it feels nice to know it's always 2 bytes and not >> have to worry about a missing colon or a missing nul terminator risking >> a buffer overflow. > > There cannot be buffer overflow, because the length of each digest > field is known. > > Roberto >
I was not referring to the digest, but the digest algorithm.
I wanted opinions on the colon and null terminated string format for algorithm identifiers.
The TCG standard log uses the TCG standard enumerations. They're always exactly 2 bytes. Parsing is trivial.
If IMA uses strings, the attacker can send, e.g., sha1: and not null terminate it. A careful parser can go a byte at a time until it reaches a maximum length - if you specify a maximum length. But it is an attack surface. Is there a corresponding advantage?
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