Messages in this thread | | | Subject | Re: [PATCH 3/4] integrity: IMA as an integrity service provider | From | Dave Hansen <> | Date | Thu, 20 Nov 2008 13:22:21 -0800 |
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On Thu, 2008-11-20 at 11:43 -0500, Mimi Zohar wrote: > > + /* Invalidate PCR, if a measured file is already open for read > */ > + if ((mask == MAY_WRITE) || (mask == MAY_APPEND)) { > + int mask_sav = data->mask; > + int rc; > + > + data->mask = MAY_READ; > + rc = ima_must_measure(&idata); > + if (!rc) { > + if (atomic_read(&(data->dentry->d_count)) - 1 > > + atomic_read(&(inode->i_writecount))) > + ima_add_violation(inode, data->filename, > + "invalid_pcr", "ToMToU"); > + } > + data->mask = mask_sav; > + goto out; > + }
Following up on Christoph's comment...
I'm worried that this calculation isn't very precise. The calculation that you're trying to come up with here is the number of opens (d_count) vs. the number of writers (i_writecount). When they don't match, you know that the new open is the first write, and you must 'invalidate the PCR'?
There are a number of things that elevate d_count, and it is a lot more than just an open() that can do it. Is that OK?
-- Dave
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