Subject: [PATCH v5] util: Set SIGPIPE to a no-op handler in virFork Libvirtd has set SIGPIPE to ignored, and virFork resets all signal handlers to the defaults. But child process may write logs to stderr/stdout, that may generate SIGPIPE if journald has stopped. So set SIGPIPE to a dummy no-op handler before unmask signals in virFork. And there is no need to set SIGPIPE ignored before running hooks in virExec. At last, set SIGPIPE to defaults before execve. Signed-off-by: Wang Yechao <wang.yechao255(a)zte.com.cn&gt; --- v3 patch: https://www.redhat.com/archives/libvir-list/2019-October/msg00934.html Changes in v4: - don't block SIGPIPE, ignore it when invoke VIR_FORCE_CLOSE and virCommandMassClose Changes in v5: - chang from SIG_IGN to a no-op handler in child process --- src/util/vircommand.c | 27 ++++++++++----------------- 1 file changed, 10 insertions(+), 17 deletions(-) diff --git a/src/util/vircommand.c b/src/util/vircommand.c index 93b3dd2..c13739c 100644 --- a/src/util/vircommand.c +++ b/src/util/vircommand.c @@ -217,6 +217,8 @@ virCommandFDSet(virCommandPtr cmd, #ifndef WIN32 +static void virDummyHandler(int sig G_GNUC_UNUSED) {} + /** * virFork: * @@ -312,6 +314,9 @@ virFork(void) ignore_value(sigaction(i, &sig_action, NULL)); } + sig_action.sa_handler = virDummyHandler; + ignore_value(sigaction(SIGPIPE, &sig_action, NULL)); + /* Unmask all signals in child, since we've no idea what the * caller's done with their signal mask and don't want to * propagate that to children */ @@ -550,7 +555,7 @@ virExec(virCommandPtr cmd) g_autofree char *binarystr = NULL; const char *binary = NULL; int ret; - struct sigaction waxon, waxoff; + struct sigaction sig_action; g_autofree gid_t *groups = NULL; int ngroups; @@ -718,21 +723,6 @@ virExec(virCommandPtr cmd) } } - /* virFork reset all signal handlers to the defaults. - * This is good for the child process, but our hook - * risks running something that generates SIGPIPE, - * so we need to temporarily block that again - */ - memset(&waxoff, 0, sizeof(waxoff)); - waxoff.sa_handler = SIG_IGN; - sigemptyset(&waxoff.sa_mask); - memset(&waxon, 0, sizeof(waxon)); - if (sigaction(SIGPIPE, &waxoff, &waxon) < 0) { - virReportSystemError(errno, "%s", - _("Could not disable SIGPIPE")); - goto fork_error; - } - if (virProcessSetMaxMemLock(0, cmd->maxMemLock) < 0) goto fork_error; if (virProcessSetMaxProcesses(0, cmd->maxProcesses) < 0) @@ -783,7 +773,10 @@ virExec(virCommandPtr cmd) if (virCommandHandshakeChild(cmd) < 0) goto fork_error; - if (sigaction(SIGPIPE, &waxon, NULL) < 0) { + memset(&sig_action, 0, sizeof(sig_action)); + sig_action.sa_handler = SIG_DFL; + sigemptyset(&sig_action.sa_mask); + if (sigaction(SIGPIPE, &sig_action, NULL) < 0) { virReportSystemError(errno, "%s", _("Could not re-enable SIGPIPE")); goto fork_error;

> @@ -783,7 +773,10 @@ virExec(virCommandPtr cmd) > if (virCommandHandshakeChild(cmd) < 0) > goto fork_error; > > - if (sigaction(SIGPIPE, &waxon, NULL) < 0) { > + memset(&sig_action, 0, sizeof(sig_action)); > + sig_action.sa_handler = SIG_DFL; > + sigemptyset(&sig_action.sa_mask); > + if (sigaction(SIGPIPE, &sig_action, NULL) < 0) { > virReportSystemError(errno, "%s", > _("Could not re-enable SIGPIPE")); > goto fork_error; We can just delete this sigaction() call entirely. The execve() call will purge the no-op handler function we registered in virFork(), resetting it back to SIG_DFL, so no need todo it manually here.