From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on dcvr.yhbt.net X-Spam-Level: X-Spam-ASN: AS31976 209.132.180.0/23 X-Spam-Status: No, score=-4.4 required=3.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,RCVD_IN_DNSWL_HI, RP_MATCHES_RCVD shortcircuit=no autolearn=ham autolearn_force=no version=3.4.0 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by dcvr.yhbt.net (Postfix) with ESMTP id 2700420960 for ; Thu, 13 Apr 2017 18:33:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755510AbdDMSdV (ORCPT ); Thu, 13 Apr 2017 14:33:21 -0400 Received: from mail-pf0-f180.google.com ([209.85.192.180]:36218 "EHLO mail-pf0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755667AbdDMSdP (ORCPT ); Thu, 13 Apr 2017 14:33:15 -0400 Received: by mail-pf0-f180.google.com with SMTP id o126so32061406pfb.3 for ; Thu, 13 Apr 2017 11:33:09 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=from:to:cc:subject:date:message-id:in-reply-to:references; bh=dyT4GXrCBfJ4OmkEnS5fTbyc07J4vqx5lmgVcIirqLg=; b=MP3qDfuZqUkfabQPI5hDyrWEtF1iSkhmzH/GWskJ7x9K1HFwvMjIcw3q1eRXbiHU+X ixeJwDIaQtbmoUx11+tTRFmjXXe79H8YAB1QekndejyceN4Iz+nXC+QlLlAnLIm62tgd ZpwXaK3k7vhy7hrSlw/7QzIF8xNLbuhcNrZ5EBmdarusX/gcWlPOmQjXHF5ek4zCNxIM e+1l/2NQOOq4HNhd9qngQsRwTnKINGumbNALXhr2XvSyBgS99TQvb4ofRnDYUdRQRfCP Ww5ZFKJwNfP4liz8GUunsCg4C7X4Nmh5olm5Znpb15wIlbHyuQ21jgI5vMkB6nCOMIJ4 VNzg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references; bh=dyT4GXrCBfJ4OmkEnS5fTbyc07J4vqx5lmgVcIirqLg=; b=juU3uvmRN52onhO3bLT6WqQ2NZAoO+niOKbTVpyA9wIKvw3bZfmm+oirITqrv7Tvk3 kZ0fVx3DA8U0/8MK9tx/eW7sV7gZILgKrsAG2vH8k56R8oAqbsC/EjUE3Q+gXXEw2G31 lX9GyKT6X9mmOZCmCbr+r/QyOv2C4EVGSXV4ceDaQQSGu/7c3gMxtjUaYWynLv0v9ELe 6Ng0CwfYZgzMs1fUIcUfy6IN2osDvZfim6YtIMdl1aMB4d4J3ikK+OS0VekTKBlYIRAm YhjA5jNSuIoIgs96IJ1S7GtbpwGvdw1dDl0wm+XrvZKwIxZ5tl8kvjYqjGqHgi5cUl0Z AhYw== X-Gm-Message-State: AN3rC/6SIwrEasGPINufYbQ5zxW8N+rAVBYkm1n0VkHv9xql5I75ikmq IOfC4zWEVDSMDs2N X-Received: by 10.99.174.69 with SMTP id e5mr3111306pgp.161.1492108388643; Thu, 13 Apr 2017 11:33:08 -0700 (PDT) Received: from roshar.mtv.corp.google.com ([100.96.238.26]) by smtp.gmail.com with ESMTPSA id 201sm43764654pfc.126.2017.04.13.11.33.07 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Thu, 13 Apr 2017 11:33:07 -0700 (PDT) From: Brandon Williams To: git@vger.kernel.org Cc: Brandon Williams , jrnieder@gmail.com, e@80x24.org Subject: [PATCH v2 5/6] run-command: eliminate calls to error handling functions in child Date: Thu, 13 Apr 2017 11:32:51 -0700 Message-Id: <20170413183252.4713-6-bmwill@google.com> X-Mailer: git-send-email 2.12.2.762.g0e3151a226-goog In-Reply-To: <20170413183252.4713-1-bmwill@google.com> References: <20170410234919.34586-1-bmwill@google.com> <20170413183252.4713-1-bmwill@google.com> Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org All of our standard error handling paths have the potential to call malloc or take stdio locks; so we must avoid them inside the forked child. Instead, the child only writes an 8 byte struct atomically to the parent through the notification pipe to propagate an error. All user-visible error reporting happens from the parent; even avoiding functions like atexit(3) and exit(3). Helped-by: Eric Wong Signed-off-by: Brandon Williams --- run-command.c | 121 ++++++++++++++++++++++++++++++++++++++++++---------------- 1 file changed, 89 insertions(+), 32 deletions(-) diff --git a/run-command.c b/run-command.c index 6751b8319..4230c4933 100644 --- a/run-command.c +++ b/run-command.c @@ -211,14 +211,82 @@ static const char **prepare_shell_cmd(struct argv_array *out, const char **argv) #ifndef GIT_WINDOWS_NATIVE static int child_notifier = -1; -static void notify_parent(void) +enum child_errcode { + CHILD_ERR_CHDIR, + CHILD_ERR_ENOENT, + CHILD_ERR_SILENT, + CHILD_ERR_ERRNO, +}; + +struct child_err { + enum child_errcode err; + int syserr; /* errno */ +}; + +static void child_die(enum child_errcode err) { - /* - * execvp failed. If possible, we'd like to let start_command - * know, so failures like ENOENT can be handled right away; but - * otherwise, finish_command will still report the error. - */ - xwrite(child_notifier, "", 1); + struct child_err buf; + + buf.err = err; + buf.syserr = errno; + + /* write(2) on buf smaller than PIPE_BUF (min 512) is atomic: */ + xwrite(child_notifier, &buf, sizeof(buf)); + _exit(1); +} + +/* + * parent will make it look like the child spewed a fatal error and died + * this is needed to prevent changes to t0061. + */ +static void fake_fatal(const char *err, va_list params) +{ + vreportf("fatal: ", err, params); +} + +static void child_error_fn(const char *err, va_list params) +{ + const char msg[] = "error() should not be called in child\n"; + xwrite(2, msg, sizeof(msg) - 1); +} + +static void child_warn_fn(const char *err, va_list params) +{ + const char msg[] = "warn() should not be called in child\n"; + xwrite(2, msg, sizeof(msg) - 1); +} + +static void NORETURN child_die_fn(const char *err, va_list params) +{ + const char msg[] = "die() should not be called in child\n"; + xwrite(2, msg, sizeof(msg) - 1); + _exit(2); +} + +/* this runs in the parent process */ +static void child_err_spew(struct child_process *cmd, struct child_err *cerr) +{ + static void (*old_errfn)(const char *err, va_list params); + + old_errfn = get_error_routine(); + set_error_routine(fake_fatal); + errno = cerr->syserr; + + switch (cerr->err) { + case CHILD_ERR_CHDIR: + error_errno("exec '%s': cd to '%s' failed", + cmd->argv[0], cmd->dir); + break; + case CHILD_ERR_ENOENT: + error_errno("cannot run %s", cmd->argv[0]); + break; + case CHILD_ERR_SILENT: + break; + case CHILD_ERR_ERRNO: + error_errno("cannot exec '%s'", cmd->argv[0]); + break; + } + set_error_routine(old_errfn); } static void prepare_cmd(struct argv_array *out, const struct child_process *cmd) @@ -355,13 +423,6 @@ static int wait_or_whine(pid_t pid, const char *argv0, int in_signal) code += 128; } else if (WIFEXITED(status)) { code = WEXITSTATUS(status); - /* - * Convert special exit code when execvp failed. - */ - if (code == 127) { - code = -1; - failed_errno = ENOENT; - } } else { error("waitpid is confused (%s)", argv0); } @@ -449,6 +510,7 @@ int start_command(struct child_process *cmd) int null_fd = -1; char **childenv; struct argv_array argv = ARGV_ARRAY_INIT; + struct child_err cerr; if (pipe(notify_pipe)) notify_pipe[0] = notify_pipe[1] = -1; @@ -467,20 +529,16 @@ int start_command(struct child_process *cmd) failed_errno = errno; if (!cmd->pid) { /* - * Redirect the channel to write syscall error messages to - * before redirecting the process's stderr so that all die() - * in subsequent call paths use the parent's stderr. + * Ensure the default die/error/warn routines do not get + * called, they can take stdio locks and malloc. */ - if (cmd->no_stderr || need_err) { - int child_err = dup(2); - set_cloexec(child_err); - set_error_handle(fdopen(child_err, "w")); - } + set_die_routine(child_die_fn); + set_error_routine(child_error_fn); + set_warn_routine(child_warn_fn); close(notify_pipe[0]); set_cloexec(notify_pipe[1]); child_notifier = notify_pipe[1]; - atexit(notify_parent); if (cmd->no_stdin) dup2(null_fd, 0); @@ -515,19 +573,17 @@ int start_command(struct child_process *cmd) } if (cmd->dir && chdir(cmd->dir)) - die_errno("exec '%s': cd to '%s' failed", cmd->argv[0], - cmd->dir); + child_die(CHILD_ERR_CHDIR); execve(argv.argv[0], (char *const *) argv.argv, (char *const *) childenv); if (errno == ENOENT) { - if (!cmd->silent_exec_failure) - error("cannot run %s: %s", cmd->argv[0], - strerror(ENOENT)); - exit(127); + if (cmd->silent_exec_failure) + child_die(CHILD_ERR_SILENT); + child_die(CHILD_ERR_ENOENT); } else { - die_errno("cannot exec '%s'", cmd->argv[0]); + child_die(CHILD_ERR_ERRNO); } } if (cmd->pid < 0) @@ -538,17 +594,18 @@ int start_command(struct child_process *cmd) /* * Wait for child's exec. If the exec succeeds (or if fork() * failed), EOF is seen immediately by the parent. Otherwise, the - * child process sends a single byte. + * child process sends a child_err struct. * Note that use of this infrastructure is completely advisory, * therefore, we keep error checks minimal. */ close(notify_pipe[1]); - if (read(notify_pipe[0], ¬ify_pipe[1], 1) == 1) { + if (xread(notify_pipe[0], &cerr, sizeof(cerr)) == sizeof(cerr)) { /* * At this point we know that fork() succeeded, but exec() * failed. Errors have been reported to our stderr. */ wait_or_whine(cmd->pid, cmd->argv[0], 0); + child_err_spew(cmd, &cerr); failed_errno = errno; cmd->pid = -1; } -- 2.12.2.762.g0e3151a226-goog