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Date:   Thu, 12 Jan 2023 14:06:49 -0800
From:   Kees Cook <keescook@chromium.org>
To:     Masahiro Yamada <masahiroy@kernel.org>
Cc:     linux-kbuild@vger.kernel.org, linux-kernel@vger.kernel.org,
        Nathan Chancellor <nathan@kernel.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        Tom Rix <trix@redhat.com>, llvm@lists.linux.dev
Subject: Re: [PATCH] scripts: handle BrokenPipeError for python scripts
Message-ID: <202301121403.599806C597@keescook>
References: <20230112023006.1873859-1-masahiroy@kernel.org>
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On Thu, Jan 12, 2023 at 11:30:06AM +0900, Masahiro Yamada wrote:
>     def main():
>         try:
>             # simulate large output (your code replaces this loop)
>             for x in range(10000):
>                 print("y")
>             # flush output here to force SIGPIPE to be triggered
>             # while inside this try block.
>             sys.stdout.flush()
>         except BrokenPipeError:
>             # Python flushes standard streams on exit; redirect remaining output
>             # to devnull to avoid another BrokenPipeError at shutdown
>             devnull = os.open(os.devnull, os.O_WRONLY)
>             os.dup2(devnull, sys.stdout.fileno())
>             sys.exit(1)  # Python exits with error code 1 on EPIPE

I still think this is wrong -- they should not continue piping, and
should just die with SIGPIPE. It should simply be:

signal(SIGPIPE, SIG_DFL);

Nothing else needed. No wasted CPU cycles, shell handling continues as
per normal.

>     if __name__ == '__main__':
>         main()
> 
>   Do not set SIGPIPE’s disposition to SIG_DFL in order to avoid
>   BrokenPipeError. Doing that would cause your program to exit
>   unexpectedly whenever any socket connection is interrupted while
>   your program is still writing to it.

This advise is for socket programs, not command-line tools.


-Kees

-- 
Kees Cook