Messages in this thread | | | Date | Wed, 28 Nov 2007 18:30:40 +0000 | From | Al Viro <> | Subject | Re: Out of tree module using LSM |
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On Wed, Nov 28, 2007 at 01:15:05PM -0500, Valdis.Kletnieks@vt.edu wrote: > (Note that the concept has interesting implications in the other direction as > well - rather than stopping you from reading a file that has malware, you could > in theory write an anti-export package that would let you write onto external > memory or outbound e-mail, but prevent the write if it was corporate-sensitive > data, or whatever.
You _can_ _not_ do that. If shared mapping gets dirtied, you have no way to intercept that. At all. Especially since the page stays mapped while it is written out, so the next modification can come when hardware had already started outbound DMA and there's no way to abort it, no matter what your external scanner would do.
Folks, really, that doesn't work. At all. You can intercept all system calls you want and it will not be enough to prevent the "bad" contents from hitting the disk.
And if we are talking about the situation when files are written to in controlled way (i.e. we are not concerned with malware running on the box in question and just want to stop it from passing through mailsewer, etc.), then there's no damn need to play with LSM - just have e.g. coda with its commit-on-close and run the scanner on commit. End of story. Mind you, in such setups one would be much better off just having the mail server run the tests explicitly in the userland, along with the rest of anti-spam, etc. filters. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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