From: Timo Sirainen <timo.sirainen@open-xchange.com>
Date: Mon, 9 Nov 2020 15:35:15 +0000 (+0200)
Subject: lib: istream-chain - Avoid NULL pointer arithmetic
X-Git-Tag: 2.3.14.rc1~368
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=73ade3503a33151ea739aef04478d1ad7e42c00d;p=thirdparty%2Fdovecot%2Fcore.git

lib: istream-chain - Avoid NULL pointer arithmetic

Even though it was only doing +0. Fixes:
runtime error: applying zero offset to null pointer
---

diff --git a/src/lib/istream-chain.c b/src/lib/istream-chain.c
index 89fc86023a..e931487836 100644
--- a/src/lib/istream-chain.c
+++ b/src/lib/istream-chain.c
@@ -181,9 +181,12 @@ static bool i_stream_chain_skip(struct chain_istream *cstream)
 		bytes_skipped -= cstream->prev_stream_left;
 		cstream->prev_stream_left = 0;
 	}
-	stream->pos -= bytes_skipped;
-	stream->skip -= bytes_skipped;
-	stream->buffer += bytes_skipped;
+	if (bytes_skipped > 0) {
+		i_assert(stream->buffer != NULL);
+		stream->pos -= bytes_skipped;
+		stream->skip -= bytes_skipped;
+		stream->buffer += bytes_skipped;
+	}
 	cstream->prev_skip = stream->skip;
 	if (link == NULL || link->eof) {
 		i_assert(bytes_skipped == 0);