From mboxrd@z Thu Jan 1 00:00:00 1970 From: zohar@linux.vnet.ibm.com (Mimi Zohar) Date: Sun, 17 Sep 2017 12:15:35 -0400 Subject: [PATCH 3/3] ima: use fs method to read integrity data (updated patch description) In-Reply-To: References: <1505451494-30228-1-git-send-email-zohar@linux.vnet.ibm.com> <1505451494-30228-4-git-send-email-zohar@linux.vnet.ibm.com> <1505507142.4200.103.camel@linux.vnet.ibm.com> <20170917151757.GA14262@infradead.org> Message-ID: <1505664935.4200.191.camel@linux.vnet.ibm.com> To: linux-security-module@vger.kernel.org List-Id: linux-security-module.vger.kernel.org On Sun, 2017-09-17 at 08:28 -0700, Linus Torvalds wrote: > On Sun, Sep 17, 2017 at 8:17 AM, Christoph Hellwig wrote: > > > > Only for direct I/O, and IMA and direct I/O don't work together. > > From ima_collect_measurement: > > > > if (file->f_flags & O_DIRECT) { > > audit_cause = "failed(directio)"; > > result = -EACCES; > > goto out; > > } > > That's not the issue. > > The issue is that somebody else can come in - using direct IO - at the > same time as the first person is collecting measurements, and thus > race with the collector. > > So now the measurements are not trustworthy any more. Unless I'm missing something, that would only be possible with an IMA policy rule that permits direct IO (eg. permit_directio). ?Otherwise the direct IO is denied. > > Well, that's exactly the point of the new ->integrity_read routine > > I proposed and prototype. The important thing is that it is called > > with i_rwsem held because code mugh higher in the chain already > > acquired it, but except for that it's entirely up to the file system. > > .. and *my* point is that it's the wrong lock for actually checking > integrity (it doesn't actually guarantee exclusion, even though in > practice it's almost always the case), and so we're adding a nasty > callback that in 99% of all cases is the same as the normal read, and > we *could* have just added it with a RWF flag instead. > > Is there some reason why integrity has to use that particular lock > that is so inconvenient for the filesystems it wants to check? Originally IMA had its own lock (iint->mutex), prior to IMA-appraisal being upstreamed. ?With a separate lock, the iint->mutex and i_rwsem would be taken in reverse order in process_measurements() and in the setxattr, chown, chmod syscalls. I'm at the airport on my way back home. Mimi -- To unsubscribe from this list: send the line "unsubscribe linux-security-module" in the body of a message to majordomo at vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html