From: Jonathan Nieder <jrnieder@gmail.com>
To: Jeff King <peff@peff.net>
Cc: demerphq <demerphq@gmail.com>, Git <git@vger.kernel.org>,
"Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Subject: Re: [PATCH v2] config: avoid "write_in_full(fd, buf, len) < len" pattern
Date: Wed, 13 Sep 2017 11:24:31 -0700 [thread overview]
Message-ID: <20170913182431.GE27425@aiede.mtv.corp.google.com> (raw)
In-Reply-To: <20170913181515.p7u2ouine3ysblqc@sigill.intra.peff.net>
Jeff King wrote:
> What I missed is that copy_begin and copy_end here are actually size_t
> variables, not the pointers. Sorry for the confusion, and here's an
> updated version of the patch with this paragraph amended (the patch
> itself is identical):
Subtle. The world makes more sense now. Thanks for figuring it out.
> -- >8 --
> Subject: [PATCH] config: avoid "write_in_full(fd, buf, len) < len" pattern
>
> The return type of write_in_full() is a signed ssize_t,
> because we may return "-1" on failure (even if we succeeded
> in writing some bytes). But "len" itself is may be an
> unsigned type (the function takes a size_t, but of course we
> may have something else in the calling function). So while
> it seems like:
>
> if (write_in_full(fd, buf, len) < len)
> die_errno("write error");
>
> would trigger on error, it won't if "len" is unsigned. The
> compiler sees a signed/unsigned comparison and promotes the
> signed value, resulting in (size_t)-1, the highest possible
> size_t (or again, whatever type the caller has). This cannot
> possibly be smaller than "len", and so the conditional can
> never trigger.
>
> I scoured the code base for cases of this, but it turns out
> that these two in git_config_set_multivar_in_file_gently()
> are the only ones. Here our "len" is the difference between
> two size_t variables, making the result an unsigned size_t.
> We can fix this by just checking for a negative return value
> directly, as write_in_full() will never return any value
> except -1 or the full count.
[...]
> Reported-by: demerphq <demerphq@gmail.com>
> Signed-off-by: Jeff King <peff@peff.net>
> ---
For what it's worth,
Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>
Thank you.
Compilers' signed/unsigned comparison warning can be noisy, but I'm
starting to feel it's worth the suppression noise to turn it on when
DEVELOPER=1 anyway. What do you think? Is there a way to turn it on
selectively for certain functions on the LHS (like read() and write()
style functions)?
Sincerely,
Jonathan
next prev parent reply other threads:[~2017-09-13 18:24 UTC|newest]
Thread overview: 46+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-09-13 11:59 Bug: git branch --unset-upstream command can nuke config when disk is full demerphq
2017-09-13 12:34 ` Jeff King
2017-09-13 13:38 ` demerphq
2017-09-13 14:17 ` Jeff King
2017-09-13 14:49 ` demerphq
2017-09-13 14:51 ` Jeff King
2017-09-13 15:18 ` demerphq
2017-09-13 15:22 ` Jeff King
2017-09-13 15:49 ` demerphq
2017-09-13 17:08 ` [PATCH 0/7] config.c may fail to notice some write() failures Jeff King
2017-09-13 17:11 ` [PATCH 1/7] config: avoid "write_in_full(fd, buf, len) < len" pattern Jeff King
2017-09-13 17:47 ` Jonathan Nieder
2017-09-13 17:53 ` Jeff King
2017-09-13 17:59 ` Jonathan Nieder
2017-09-13 18:11 ` Jeff King
2017-09-13 18:15 ` [PATCH v2] " Jeff King
2017-09-13 18:24 ` Jonathan Nieder [this message]
2017-09-13 18:58 ` Jeff King
2017-09-13 19:18 ` Jonathan Nieder
2017-09-13 19:49 ` Jonathan Nieder
2017-09-13 22:43 ` Ramsay Jones
2017-09-13 23:31 ` Ramsay Jones
2017-09-15 0:37 ` Jeff King
2017-09-15 15:15 ` Ramsay Jones
2017-09-13 21:33 ` Junio C Hamano
2017-09-13 17:11 ` [PATCH 2/7] get-tar-commit-id: check write_in_full() return against 0 Jeff King
2017-09-13 17:53 ` Jonathan Nieder
2017-09-13 18:02 ` Jeff King
2017-09-13 18:37 ` Jeff King
2017-09-13 21:09 ` Jonathan Nieder
2017-09-15 0:40 ` Jeff King
2017-09-13 17:16 ` [PATCH 3/7] avoid "write_in_full(fd, buf, len) != len" pattern Jeff King
2017-09-13 21:14 ` Jonathan Nieder
2017-09-15 0:42 ` Jeff King
2017-09-13 17:16 ` [PATCH 4/7] convert less-trivial versions of "write_in_full() != len" Jeff King
2017-09-13 21:16 ` Jonathan Nieder
2017-09-13 17:17 ` [PATCH 5/7] pkt-line: check write_in_full() errors against "< 0" Jeff King
2017-09-13 21:17 ` Jonathan Nieder
2017-09-13 17:17 ` [PATCH 6/7] notes-merge: use ssize_t for write_in_full() return value Jeff King
2017-09-13 21:20 ` Jonathan Nieder
2017-09-15 0:43 ` Jeff King
2017-09-13 17:17 ` [PATCH 7/7] config: flip return value of store_write_*() Jeff King
2017-09-13 21:25 ` Jonathan Nieder
2017-09-15 0:46 ` Jeff King
2017-09-13 18:47 ` [PATCH 8/7] read_pack_header: handle signed/unsigned comparison in read result Jeff King
2017-09-13 19:11 ` Jonathan Nieder
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