On Mon, 16 Jan 2006 09:15:16 EST, "linux-os (Dick Johnson)" said: > But the customer complained during certification testing > that shared memory in use is not measured and therefore > cannot be verified. This means that there may be rogue > communications channels, using shared memory, in the > system. I need to prove that there are no such channels > by metering the shared memory and then accounting for > every bit shown. The customer is confused, and your test is broken as designed. The fact that you look in /proc/meminfo and account for every shared memory page *at this instant* doesn't mean there isn't a communication channel *at some other time*. Even if you run a daemon that does nothing but monitor this usage 10 times a second, and complain if a discrepancy is found, it *still* won't work: 1) It's racy - 2 processes can mmap() some space during that 0.1 seconds, transfer the info, and detach the memory without your knowledge. 2) It's racy - if you inquire *while* some other process is in some intermediate state, causing false positives that will drive the SSO nuts. The *proper* solution is to use something like SELinux that will flat-out *prohibit* the attachment of a shared memory segment that isn't permitted.
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