Re: [libvirt] [PATCH 5/5] qemu: support use of virtlogd with file based chardevs

Currently the file based character devices let QEMU write directly to a file on disk. This allows a malicious QEMU to inflict a denial of service by consuming all free space. Switch QEMU to use a pipe to virtlogd, which will enforce file rollover. Signed-off-by: Daniel P. Berrange <berrange(a)redhat.com&gt; --- src/qemu/qemu_command.c | 50 ++++++++++++++++++++++++++++++++++++++++--------- 1 file changed, 41 insertions(+), 9 deletions(-) diff --git a/src/qemu/qemu_command.c b/src/qemu/qemu_command.c index 8378470..9ed1b97 100644 --- a/src/qemu/qemu_command.c +++ b/src/qemu/qemu_command.c @@ -3934,17 +3934,49 @@ qemuBuildChrChardevStr(virLogManagerPtr logManager, break; case VIR_DOMAIN_CHR_TYPE_FILE: - virBufferAsprintf(&buf, "file,id=char%s,path=%s", alias, - dev->data.file.path); - if (dev->data.file.append != VIR_TRISTATE_SWITCH_ABSENT) { - if (!virQEMUCapsGet(qemuCaps, QEMU_CAPS_CHARDEV_FILE_APPEND)) { - virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s", - _("append not supported in this QEMU binary")); + if (logManager && virQEMUCapsGet(qemuCaps, QEMU_CAPS_CHARDEV_FILE_APPEND)) { + char *fdset, *fdpath; + int flags = 0; + int logfd; + + if (dev->data.file.append == VIR_TRISTATE_SWITCH_OFF) + flags |= VIR_LOG_MANAGER_PROTOCOL_DOMAIN_OPEN_LOG_FILE_TRUNCATE; + + if ((logfd = virLogManagerDomainOpenLogFile(logManager, + "qemu", + def->uuid, + def->name, + dev->data.file.path, + flags, + NULL, NULL)) < 0) goto error; - } - virBufferAsprintf(&buf, ",append=%s", - virTristateSwitchTypeToString(dev->data.file.append)); + virCommandPassFD(cmd, logfd, VIR_COMMAND_PASS_FD_CLOSE_PARENT); + if (!(fdset = qemuVirCommandGetFDSet(cmd, logfd))) + goto error; + + virCommandAddArg(cmd, "-add-fd"); + virCommandAddArg(cmd, fdset); + VIR_FREE(fdset); + + if (!(fdpath = qemuVirCommandGetDevSet(cmd, logfd))) + goto error; + + virBufferAsprintf(&buf, "file,id=char%s,path=%s,append=on", alias, fdpath); + VIR_FREE(fdpath);

+ } else { + virBufferAsprintf(&buf, "file,id=char%s,path=%s", alias, + dev->data.file.path); + if (dev->data.file.append != VIR_TRISTATE_SWITCH_ABSENT) { + if (!virQEMUCapsGet(qemuCaps, QEMU_CAPS_CHARDEV_FILE_APPEND)) { + virReportError(VIR_ERR_CONFIG_UNSUPPORTED, "%s", + _("append not supported in this QEMU binary")); + goto error; + } + + virBufferAsprintf(&buf, ",append=%s", + virTristateSwitchTypeToString(dev->data.file.append)); + } } break;