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=-3.9 required=3.0 tests=AWL,BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,RCVD_IN_DNSWL_HI, RCVD_IN_SORBS_SPAM,RP_MATCHES_RCVD shortcircuit=no autolearn=no 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 530411FE90 for ; Wed, 19 Apr 2017 23:14:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S940324AbdDSXOM (ORCPT ); Wed, 19 Apr 2017 19:14:12 -0400 Received: from mail-io0-f177.google.com ([209.85.223.177]:33300 "EHLO mail-io0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S938306AbdDSXOG (ORCPT ); Wed, 19 Apr 2017 19:14:06 -0400 Received: by mail-io0-f177.google.com with SMTP id k87so42197281ioi.0 for ; Wed, 19 Apr 2017 16:14:01 -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=OX8Bf+ZSeMo9b48es543s1tqYg5MQ4XUDLcloQLZ0Ck=; b=NZjULaEDJruOLBd0W2YkQybGCU4JNUKD/gw+WPFNjebIFPQ9kHww5Tf/MZRg2L+MKR d/2y5QmiNTFHVmsobOePYGPQm9QeVB+ApxUOkfRDghF7QDD5EoQBQrvgO6QGlUo0zq7h 9uc5dvmO+kYyfbZgkwU82ODr6zw/Sxxri8G3wVI/UArfBNGE4vqoKnjZExmt/D0uo0mF nCVWmCkCIz6vOL+sXCNQ5CGPizrKj350qci2Z/KOamXzIRr21LqGY9P3Wt9DfIj3Wnj0 9H5M+0j+HzF6TVivs585zAWpXIb8ZxLIPbH21WS9IjTJuZThSbkQwTcur1lNGc7AmZp9 qKSg== 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=OX8Bf+ZSeMo9b48es543s1tqYg5MQ4XUDLcloQLZ0Ck=; b=IAY4Rm1grBpz767z61OccU3ClZLVvT3F1kpkoWu42eq61xnHuXoLk+W2Rm/NznOdbN FuMir677K6dansmYGNe9niugZhMAHlpD2nAm4vZNrH+1E1XExc2iyZwntvcjSUzx7cl0 wXXhg9+IDvgRWQKdpi6ZqDSnKb3SC3kvNivxDDLFYnBmAN3HDI9O7csHcIuBjqZ82xVF 1NgUsNd5zgG/ACIk3BngK3K0m3xplyv0hhzvKHUQIW0rWX17icD7cWEV0QI7GJjCgjhC fHgz1oK95+zaGWfiKEQNfzWHt60+ksZwC5nXVx8r61TGICemG9kKHmR6opc1l6SyY9KB Royg== X-Gm-Message-State: AN3rC/6txMet5dHmtaaAb1ntnuc9hJ+092qm3K9X2gp4HpEt4NQMZOse 701WmO+ML/tpVHT7 X-Received: by 10.98.210.2 with SMTP id c2mr5407627pfg.83.1492643631077; Wed, 19 Apr 2017 16:13:51 -0700 (PDT) Received: from roshar.svl.corp.google.com ([100.96.218.30]) by smtp.gmail.com with ESMTPSA id s10sm6433798pfe.28.2017.04.19.16.13.49 (version=TLS1_2 cipher=ECDHE-RSA-AES128-SHA bits=128/128); Wed, 19 Apr 2017 16:13:49 -0700 (PDT) From: Brandon Williams To: git@vger.kernel.org Cc: Eric Wong , j6t@kdbg.org, sbeller@google.com, jrnieder@gmail.com, Brandon Williams Subject: [PATCH v6 11/11] run-command: block signals between fork and execve Date: Wed, 19 Apr 2017 16:13:27 -0700 Message-Id: <20170419231327.49895-12-bmwill@google.com> X-Mailer: git-send-email 2.12.2.816.g2cccc81164-goog In-Reply-To: <20170419231327.49895-1-bmwill@google.com> References: <20170418231805.61835-1-bmwill@google.com> <20170419231327.49895-1-bmwill@google.com> Sender: git-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org From: Eric Wong Signal handlers of the parent firing in the forked child may have unintended side effects. Rather than auditing every signal handler we have and will ever have, block signals while forking and restore default signal handlers in the child before execve. Restoring default signal handlers is required because execve does not unblock signals, it only restores default signal handlers. So we must restore them with sigprocmask before execve, leaving a window when signal handlers we control can fire in the child. Continue ignoring ignored signals, but reset the rest to defaults. Similarly, disable pthread cancellation to future-proof our code in case we start using cancellation; as cancellation is implemented with signals in glibc. Signed-off-by: Eric Wong Signed-off-by: Brandon Williams --- run-command.c | 68 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 68 insertions(+) diff --git a/run-command.c b/run-command.c index df1edd963..a97d7bf9f 100644 --- a/run-command.c +++ b/run-command.c @@ -215,6 +215,7 @@ enum child_errcode { CHILD_ERR_CHDIR, CHILD_ERR_DUP2, CHILD_ERR_CLOSE, + CHILD_ERR_SIGPROCMASK, CHILD_ERR_ENOENT, CHILD_ERR_SILENT, CHILD_ERR_ERRNO @@ -303,6 +304,9 @@ static void child_err_spew(struct child_process *cmd, struct child_err *cerr) case CHILD_ERR_CLOSE: error_errno("close() in child failed"); break; + case CHILD_ERR_SIGPROCMASK: + error_errno("sigprocmask failed restoring signals"); + break; case CHILD_ERR_ENOENT: error_errno("cannot run %s", cmd->argv[0]); break; @@ -398,7 +402,54 @@ static char **prep_childenv(const char *const *deltaenv) strbuf_release(&key); return childenv; } + +struct atfork_state { +#ifndef NO_PTHREADS + int cs; #endif + sigset_t old; +}; + +#ifndef NO_PTHREADS +static void bug_die(int err, const char *msg) +{ + if (err) { + errno = err; + die_errno("BUG: %s", msg); + } +} +#endif + +static void atfork_prepare(struct atfork_state *as) +{ + sigset_t all; + + if (sigfillset(&all)) + die_errno("sigfillset"); +#ifdef NO_PTHREADS + if (sigprocmask(SIG_SETMASK, &all, &as->old)) + die_errno("sigprocmask"); +#else + bug_die(pthread_sigmask(SIG_SETMASK, &all, &as->old), + "blocking all signals"); + bug_die(pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &as->cs), + "disabling cancellation"); +#endif +} + +static void atfork_parent(struct atfork_state *as) +{ +#ifdef NO_PTHREADS + if (sigprocmask(SIG_SETMASK, &as->old, NULL)) + die_errno("sigprocmask"); +#else + bug_die(pthread_setcancelstate(as->cs, NULL), + "re-enabling cancellation"); + bug_die(pthread_sigmask(SIG_SETMASK, &as->old, NULL), + "restoring signal mask"); +#endif +} +#endif /* GIT_WINDOWS_NATIVE */ static inline void set_cloexec(int fd) { @@ -523,6 +574,7 @@ int start_command(struct child_process *cmd) char **childenv; struct argv_array argv = ARGV_ARRAY_INIT; struct child_err cerr; + struct atfork_state as; if (pipe(notify_pipe)) notify_pipe[0] = notify_pipe[1] = -1; @@ -536,6 +588,7 @@ int start_command(struct child_process *cmd) prepare_cmd(&argv, cmd); childenv = prep_childenv(cmd->env); + atfork_prepare(&as); /* * NOTE: In order to prevent deadlocking when using threads special @@ -549,6 +602,7 @@ int start_command(struct child_process *cmd) cmd->pid = fork(); failed_errno = errno; if (!cmd->pid) { + int sig; /* * Ensure the default die/error/warn routines do not get * called, they can take stdio locks and malloc. @@ -597,6 +651,19 @@ int start_command(struct child_process *cmd) child_die(CHILD_ERR_CHDIR); /* + * restore default signal handlers here, in case + * we catch a signal right before execve below + */ + for (sig = 1; sig < NSIG; sig++) { + /* ignored signals get reset to SIG_DFL on execve */ + if (signal(sig, SIG_DFL) == SIG_IGN) + signal(sig, SIG_IGN); + } + + if (sigprocmask(SIG_SETMASK, &as.old, NULL) != 0) + child_die(CHILD_ERR_SIGPROCMASK); + + /* * Attempt to exec using the command and arguments starting at * argv.argv[1]. argv.argv[0] contains SHELL_PATH which will * be used in the event exec failed with ENOEXEC at which point @@ -616,6 +683,7 @@ int start_command(struct child_process *cmd) child_die(CHILD_ERR_ERRNO); } } + atfork_parent(&as); if (cmd->pid < 0) error_errno("cannot fork() for %s", cmd->argv[0]); else if (cmd->clean_on_exit) -- 2.12.2.816.g2cccc81164-goog