From 83f0d0da53b1516d9be55d7f60e82dfd1efd95b9 Mon Sep 17 00:00:00 2001 From: dim Date: Sun, 18 Dec 2016 14:31:11 +0000 Subject: [PATCH] MFC r310013 (by cperciva): 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. MFC r310086: In xbd_connect(), use correct scanf conversion specifiers for the feature_barrier and feature_flush variables. Otherwise, adjacent variables on the stack, such as sector_size, may be overwritten, with disastrous results. Note that I did not see a good reason to revert the addition of zero checks introduced in r310013. Better safe than sorry. PR: 215209 Tested by: royger git-svn-id: svn://svn.freebsd.org/base/stable/10@310228 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f --- sys/dev/xen/blkfront/blkfront.c | 12 ++++++++++-- 1 file changed, 10 insertions(+), 2 deletions(-) diff --git a/sys/dev/xen/blkfront/blkfront.c b/sys/dev/xen/blkfront/blkfront.c index 1ad249402..58ddd804e 100644 --- a/sys/dev/xen/blkfront/blkfront.c +++ b/sys/dev/xen/blkfront/blkfront.c @@ -1239,19 +1239,27 @@ 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); if (err || phys_sector_size <= sector_size) phys_sector_size = 0; err = xs_gather(XST_NIL, xenbus_get_otherend_path(dev), - "feature-barrier", "%lu", &feature_barrier, + "feature-barrier", "%d", &feature_barrier, NULL); if (err == 0 && feature_barrier != 0) sc->xbd_flags |= XBDF_BARRIER; err = xs_gather(XST_NIL, xenbus_get_otherend_path(dev), - "feature-flush-cache", "%lu", &feature_flush, + "feature-flush-cache", "%d", &feature_flush, NULL); if (err == 0 && feature_flush != 0) sc->xbd_flags |= XBDF_FLUSH; -- 2.45.0