[libvirt] [PATCH v5] util: Set SIGPIPE to a no-op handler in virFork

[wang.yechao255 at zte.com.cn]

ping.
> 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 at zte.com.cn>
> ---
> 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;

---
Best wishes
Wang Yechao