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SubjectRe: [PATCH v1] LSM: Enable multiple calls to security_add_hooks() for the same LSM

On 30/04/2017 04:11, Tetsuo Handa wrote:
> Casey Schaufler wrote:
>> On 4/29/2017 12:02 PM, Mickael Salaun wrote:
>>> Check if the registering LSM already registered hooks just before. This
>>> enable to split hook declarations into multiple files without
>>> registering multiple time the same LSM name, starting from commit
>>> d69dece5f5b6 ("LSM: Add /sys/kernel/security/lsm").
>> What's special about the previous registration? Keep it
>> simple and check it the name is already anywhere on the
>> list and only add it if it's not already there. I don't
>> see advantage to:
>> % cat /sys/kernel/security/lsm
>> capability,yama,spiffy,selinux,spiffy
>> over
>> % cat /sys/kernel/security/lsm
>> capability,yama,spiffy,selinux

That was my first though, but then I realized that I don't see any use
case where an LSM would register hooks interleaved with other LSM. I
find the current approach simpler because we only search from the end of
the string and we do not handle special cases (e.g. matching only a
sub-name). Moreover, this approach respects the semantic describe in
Documentation/security/LSM.txt: "The list reflects the order in which
checks are made".

> - if (lsm_append(lsm, &lsm_names) < 0)
> + if (lsm && lsm_append(lsm, &lsm_names) < 0)
> in security_add_hooks()?

That was considered
but Kees and Casey seem to prefer the current approach.

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