Date: Tue, 13 Dec 2016 06:54:13 +0000 (UTC) From: Colin Percival <cperciva@FreeBSD.org> To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r310013 - head/sys/dev/xen/blkfront Message-ID: <201612130654.uBD6sDtF073358@repo.freebsd.org>
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Author: cperciva Date: Tue Dec 13 06:54:13 2016 New Revision: 310013 URL: https://svnweb.freebsd.org/changeset/base/310013 Log: Check that blkfront devices have a non-zero number of sectors and a non-zero sector size. Such a device would be a virtual disk of zero bytes; clearly not useful, and not something we should try to attach. As a fortuitous side effect, checking that these values are non-zero here results in them not *becoming* zero later on the function. This odd behaviour began with r309124 (clang 3.9.0) but is challenging to debug; making any changes to this function whatsoever seems to affect the llvm optimizer behaviour enough to make the unexpected zeroing of the sector_size variable cease. PR: 215209 Security: The potential for variables to unexpectedly become zero has worrying consequences for security in general, but not so much in this particular context. Modified: head/sys/dev/xen/blkfront/blkfront.c Modified: head/sys/dev/xen/blkfront/blkfront.c ============================================================================== --- head/sys/dev/xen/blkfront/blkfront.c Tue Dec 13 05:09:49 2016 (r310012) +++ head/sys/dev/xen/blkfront/blkfront.c Tue Dec 13 06:54:13 2016 (r310013) @@ -1245,6 +1245,14 @@ xbd_connect(struct xbd_softc *sc) xenbus_get_otherend_path(dev)); return; } + if ((sectors == 0) || (sector_size == 0)) { + xenbus_dev_fatal(dev, 0, + "invalid parameters from %s:" + " sectors = %lu, sector_size = %lu", + xenbus_get_otherend_path(dev), + sectors, sector_size); + return; + } err = xs_gather(XST_NIL, xenbus_get_otherend_path(dev), "physical-sector-size", "%lu", &phys_sector_size, NULL);
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