[PATCH 0/2] qemu_process: Start QEMU for caps probing more robustly
I'm not going to lie, my true motive is to be able to have a very small bash wrapper that spawns QEMU under valgrind, e.g. like this: #!/bin/bash exec /usr/bin/valgrind --tool=memcheck --leak-check=full \ --track-fds=yes --log-file=/tmp/valgrind_qemu.log \ qemu-system-x86_64 "$@" But if a malicious user provides slightly different script (see 2/2) then they can starve libvirt worker pool. Hence, we have two reasons for merging these. Michal Prívozník (2): qemu_process: Be nicer to killing QEMU when probing caps qemu_process: Start QEMU for caps probing more robustly src/qemu/qemu_process.c | 64 +++++++++++++++++++++++++++-------------- src/qemu/qemu_process.h | 1 - 2 files changed, 43 insertions(+), 22 deletions(-) -- 2.34.1
The qemuProcessQMPStop() function is intended to kill this dummy QEMU process we started only for querying capabilities. Nevertheless, it may be not plain QEMU binary we executed, but in fact it may be a memcheck tool (e.g. valgrind) that executes QEMU later. By switching to virProcessKillPainfully() we allow this wrapper tool to exit gracefully. Another up side is that virProcessKillPainfully() reports an error so no need for us to VIR_ERROR() ourselves. Signed-off-by: Michal Privoznik <mprivozn@redhat.com> --- src/qemu/qemu_process.c | 6 +----- 1 file changed, 1 insertion(+), 5 deletions(-) diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c index ea586e54c1..bb7d02f6c7 100644 --- a/src/qemu/qemu_process.c +++ b/src/qemu/qemu_process.c @@ -9095,11 +9095,7 @@ qemuProcessQMPStop(qemuProcessQMP *proc) if (proc->pid != 0) { VIR_DEBUG("Killing QMP caps process %lld", (long long)proc->pid); - if (virProcessKill(proc->pid, SIGKILL) < 0 && errno != ESRCH) - VIR_ERROR(_("Failed to kill process %lld: %s"), - (long long)proc->pid, - g_strerror(errno)); - + virProcessKillPainfully(proc->pid, true); proc->pid = 0; } -- 2.34.1
When probing QEMU capabilities, we look at whatever <emulator/> was specified in the domain XML and execute it with couple of arguments (-daemonize being one of them) Then, we use virCommandSetErrorBuffer() to read stderr of the child process hoping to read possible error message just before the process daemonized itself. Well, this works as long as the emulator binary behaves. If the binary is evil and basically does the following: #!/bin/bash sleep 1h then virCommandRun() called from qemuProcessQMPLaunch() doesn't return for whole hour (because it's stuck in reading stderr of the child process). This behavior of ours is very suboptimal. The solution is to not rely on the binary behaving correctly on -daemonize argument but to daemonize the process ourselves (via virCommandDaemonize()) and then wait for the monitor to show up with a timeout. This in turn means, that we can no longer use virCommandSetErrorBuffer() but we can do the equivalent with virCommandSetErrorFD() and a bit of code. Sure, this doesn't shield us from malicious binaries 100% but helps preventing depletion of worker threads. Signed-off-by: Michal Privoznik <mprivozn@redhat.com> --- src/qemu/qemu_process.c | 58 +++++++++++++++++++++++++++++------------ src/qemu/qemu_process.h | 1 - 2 files changed, 42 insertions(+), 17 deletions(-) diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c index bb7d02f6c7..9ba7a11676 100644 --- a/src/qemu/qemu_process.c +++ b/src/qemu/qemu_process.c @@ -9129,7 +9129,6 @@ qemuProcessQMPFree(qemuProcessQMP *proc) g_free(proc->monpath); g_free(proc->monarg); g_free(proc->pidfile); - g_free(proc->stdErr); g_free(proc); } @@ -9248,7 +9247,9 @@ static int qemuProcessQMPLaunch(qemuProcessQMP *proc) { const char *machine; - int status = 0; + VIR_AUTOCLOSE errfd = -1; + virTimeBackOffVar timebackoff; + const unsigned long long timeout = 30 * 1000; /* ms */ int rc; if (proc->forceTCG) @@ -9273,9 +9274,7 @@ qemuProcessQMPLaunch(qemuProcessQMP *proc) "-nographic", "-machine", machine, "-qmp", proc->monarg, - "-pidfile", proc->pidfile, - "-daemonize", - NULL); + NULL); virCommandAddEnvPassCommon(proc->cmd); virCommandClearCaps(proc->cmd); @@ -9289,26 +9288,53 @@ qemuProcessQMPLaunch(qemuProcessQMP *proc) virCommandSetGID(proc->cmd, proc->runGid); virCommandSetUID(proc->cmd, proc->runUid); - virCommandSetErrorBuffer(proc->cmd, &(proc->stdErr)); + virCommandSetPidFile(proc->cmd, proc->pidfile); + virCommandSetErrorFD(proc->cmd, &errfd); + virCommandDaemonize(proc->cmd); - if (virCommandRun(proc->cmd, &status) < 0) + if (virCommandRun(proc->cmd, NULL) < 0) return -1; - if (status != 0) { - VIR_DEBUG("QEMU %s exited with status %d", proc->binary, status); - virReportError(VIR_ERR_INTERNAL_ERROR, - _("Failed to start QEMU binary %s for probing: %s"), - proc->binary, - proc->stdErr ? proc->stdErr : _("unknown error")); - return -1; - } - if ((rc = virPidFileReadPath(proc->pidfile, &proc->pid)) < 0) { virReportSystemError(-rc, _("Failed to read pidfile %s"), proc->pidfile); return -1; } + if (virTimeBackOffStart(&timebackoff, 1, timeout) < 0) + goto error; + while (virTimeBackOffWait(&timebackoff)) { + char errbuf[1024] = { 0 }; + + if (virFileExists(proc->monpath)) + break; + + if (virProcessKill(proc->pid, 0) == 0) + continue; + + ignore_value(saferead(errfd, errbuf, sizeof(errbuf) - 1)); + virReportError(VIR_ERR_INTERNAL_ERROR, + _("Failed to start QEMU binary %s for probing: %s"), + proc->binary, + errbuf[0] ? errbuf : _("unknown error")); + goto error; + } + + if (!virFileExists(proc->monpath)) { + virReportError(VIR_ERR_OPERATION_TIMEOUT, "%s", + _("QEMU monitor did not show up")); + goto error; + } + return 0; + + error: + virCommandAbort(proc->cmd); + if (proc->pid >= 0) + virProcessKillPainfully(proc->pid, true); + if (proc->pidfile) + unlink(proc->pidfile); + + return -1; } diff --git a/src/qemu/qemu_process.h b/src/qemu/qemu_process.h index 1b1cc489f0..e1c2c155e9 100644 --- a/src/qemu/qemu_process.h +++ b/src/qemu/qemu_process.h @@ -214,7 +214,6 @@ struct _qemuProcessQMP { char *libDir; uid_t runUid; gid_t runGid; - char *stdErr; char *monarg; char *monpath; char *pidfile; -- 2.34.1
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Michal Privoznik