From cafebee579f6a9399fbfcc86e2c89a479aee465e Mon Sep 17 00:00:00 2001
From: Julian Andres Klode <julian.klode@canonical.com>
Date: Mon, 27 Jan 2020 13:23:53 +0100
Subject: NewGroup: Create GrpIterator after allocation (fix segfault)

NewGroup created a GrpIterator and then called WriteStringInMap()
which might remap the cache, causing the iterator to go invalid.

Avoid this simply by creating the iterator later on.
---
 apt-pkg/pkgcachegen.cc | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/apt-pkg/pkgcachegen.cc b/apt-pkg/pkgcachegen.cc
index 8e0301151..dfac0ae1c 100644
--- a/apt-pkg/pkgcachegen.cc
+++ b/apt-pkg/pkgcachegen.cc
@@ -557,10 +557,11 @@ bool pkgCacheGenerator::NewGroup(pkgCache::GrpIterator &Grp, StringView Name)
    if (unlikely(Group == 0))
       return false;
 
-   Grp = pkgCache::GrpIterator(Cache, Cache.GrpP + Group);
    map_stringitem_t const idxName = WriteStringInMap(Name);
    if (unlikely(idxName == 0))
       return false;
+
+   Grp = pkgCache::GrpIterator(Cache, Cache.GrpP + Group);
    Grp->Name = idxName;
 
    // Insert it into the hash table
-- 
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