[PATCH] iconv: add check to avoid writing past end of buffer

[Will Dietz <w@wdtz.org>]

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Attached.

Example based on [1] that crashes without this fix can be found here:

https://gist.github.com/7bc07da1dcd02e01c2fbb28cbaa81420

Input is from git's tests (2.17.0), and fixes tests when using
noxcuse-based iconv utility and musl's iconv implementation.

Well, *almost*.   At least no more crashing :).  One final test
involving autosquash fails-- I believe due to a comparison breaking
due to unexpected shifts in ISO-2022-JP encoding (as described in [2])
but I'm not sure of details just yet.  Neat to get this far!

~Will

[1] http://www.openwall.com/lists/musl/2017/05/03/1
[2] http://www.openwall.com/lists/musl/2014/11/09/1

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From d4516bbca6b315927b82252baa24574ae12f0b06 Mon Sep 17 00:00:00 2001
From: Will Dietz <w@wdtz.org>
Date: Tue, 1 May 2018 14:16:44 -0500
Subject: [PATCH] iconv.c: add missing check against output buffer size

---
 src/locale/iconv.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/locale/iconv.c b/src/locale/iconv.c
index d469856c..3c1f4dd2 100644
--- a/src/locale/iconv.c
+++ b/src/locale/iconv.c
@@ -539,6 +539,7 @@ size_t iconv(iconv_t cd, char **restrict in, size_t *restrict inb, char **restri
 			if (*outb < 1) goto toobig;
 			if (c<256 && c==legacy_map(tomap, c)) {
 			revout:
+				if (*outb < 1) goto toobig;
 				*(*out)++ = c;
 				*outb -= 1;
 				break;
-- 
2.17.0