From: Jeff King <peff@peff.net>
To: "Randall S. Becker" <rsbecker@nexbridge.com>
Cc: git@vger.kernel.org
Subject: Re: [Possible Bug] Use of write on size-limited platforms
Date: Mon, 15 Jun 2020 17:59:37 -0400 [thread overview]
Message-ID: <20200615215937.GA636737@coredump.intra.peff.net> (raw)
In-Reply-To: <015c01d63ddd$97d65080$c782f180$@nexbridge.com>
On Mon, Jun 08, 2020 at 05:41:34PM -0400, Randall S. Becker wrote:
> I just wanted to check the following calls to make sure that it does not
> fwrite or write should be xread/xwrite or are guaranteed not to exceed
> MAX_IO_SIZE:
>
> strbuf.c: strbuf_write, strbuf_write_fd, the size is not specified.
>
> The other uses of read/write appear to be safe.
strbuf_write() is using fwrite(), and we don't enforce MAX_IO_SIZE with
stdio anywhere else. And I'd expect in general that if there are any
platform limitations, the system libc would choose a sane value anyway.
So that one is probably fine.
I think strbuf_write_fd() is wrong to use a raw write(), but for several
reasons:
- it won't enforce MAX_IO_SIZE, as you note
- it won't handle EINTR, etc; callers need to be prepared to restart
such a write
- it won't handle a partial write by looping until all output is sent
For the latter two, there are cases where some callers want the
flexibility to stop when seeing a signal or a partial write. But I don't
think that makes any sense for strbuf_write_fd(). If I pass in a strbuf
with 8kb of data and I get a return value that indicates we only wrote
4kb, what do I do next? I certainly can't call strbuf_write_fd() again,
since it would write from the beginning of the strbuf again. I'd have to
call xwrite() myself after that. At which point I may as well have done
so for the first call. :)
So I think this really ought to be using write_in_full(). There's only
one caller, and I think it would be improved by the switch. Do you want
to write a patch?
You could make an argument that the fwrite() version ought to also loop,
since it's possible to get a partial write there, too. But we don't do
that in general. I suspect in practice most stdio implementations will
keep writing until they see an error, and most callers don't bother
checking stdio errors at all, or use ferror().
-Peff
next prev parent reply other threads:[~2020-06-15 21:59 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-08 21:41 [Possible Bug] Use of write on size-limited platforms Randall S. Becker
2020-06-15 21:59 ` Jeff King [this message]
2020-06-15 22:38 ` Randall S. Becker
2020-06-16 8:02 ` Jeff King
2020-06-19 15:05 ` Randall S. Becker
2020-06-19 19:35 ` Junio C Hamano
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