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    SubjectRe: [TOMOYO #8 (2.6.25-mm1) 1/7] Introduce new LSM hooks.
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    On Thu, 2008-05-01 at 08:47 -0700, Chris Wright wrote:
    > * Tetsuo Handa (penguin-kernel@I-love.SAKURA.ne.jp) wrote:
    > > The MAY_WRITE flag is not passed to security_inode_permission()
    > > if security_inode_permission() is called from __open_namei_create().
    > > Since TOMOYO Linux doesn't check MAY_READ/MAY_WRITE permissions for individual
    > > read()/write() requests, the permission checks at open() time (i.e. may_open())
    > > is the only chance to check MAY_WRITE flag. If I can't check MAY_WRITE flag
    > > here, TOMOYO Linux can't control open(O_WRONLY | O_CREATE | O_EXCL).
    > >
    > > Also, the O_TRUNC flag is not passed to security_inode_permission() because
    > > vfs_permission() receives only MAY_READ/MAY_WRITE/MAY_APPEND flags, but
    > > I have to check O_TRUNC flag before do_truncate().
    > >
    > > So, I inserted a new hook here so that this hook can check all
    > > MAY_READ/MAY_WRITE/O_APPEND/O_TRUNC flags together in a single place.
    >
    > The reason I ask is because it doesn't check. It only checks O_APPEND,
    > but that's already passed in (MAY_APPEND). So AFAICT, it's only O_TRUNC
    > that you are trying to special case. But in that case...all that is
    > being asked for is MAY_WRITE permission. Anything else doesn't make
    > sense, especially since that's all you get from the truncate(2) path.
    >
    > <snip>
    > > This is an inevitable duplication since I want to do conventional checks
    > > (DAC checks and inode operation existence checks) before TOMOYO Linux's check.
    > >
    > > By the way, Stephen Smalley thinks it is better to copy codes which is needed by
    > > pre_vfs_*() (i.e. may_create()/may_delete()/check_sticky()) into
    > > security/tomoyo/ directory and leave vfs_*() untouched rather than
    > > extract pre_vfs_*() from vfs_*() and call pre_vfs_*() from vfs_*().
    >
    > I'm not sure he means literally copy. Typically we take existing
    > functionality and make it externally usable.

    I didn't think splitting pre functions out of all of the vfs helpers was
    such a good idea. Making may_create/delete() available might make
    sense. And for complex combinations of DAC logic, perhaps introducing
    may_link(), may_rename(), etc. might make sense.

    > Also, all the changes you make that are not in vfs_* helpers won't get
    > picked up by NFS.

    --
    Stephen Smalley
    National Security Agency



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