[Bug 1061] New: mmv pmda sensitive to TOCTOU for shmem metadata extraction

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Bug ID	1061
Summary	mmv pmda sensitive to TOCTOU for shmem metadata extraction
Product	pcp
Version	unspecified
Hardware	All
OS	Linux
Status	NEW
Severity	major
Priority	P5
Component	pcp
Assignee	pcp@kenj.com.au
Reporter	fche@redhat.com
CC	pcp@oss.sgi.com
Classification	Unclassified

It appears possible for an libmmv-based application to issue mmv_stats_init(3)
calls close enough to confuse the mmv pmda.  That's because the mmv pmda only
checks the shmem g1/g2 generation numbers once, and assumes that during the 
whole need_reload==1 processing, the shmem contents will be stable.

An adequate workaround could be to have the mmv pmda copy the shmem segment
into a private copy (possibly looping if the libmmv app keeps changing
things -- but watch out for DoS!), then using the stable private copy to
populate the PMNS etc., and to compute persistent pointers to the shmem
pmAtoms.

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