Re: [PATCH] sha1_name: fix segfault caused by invalid index access

Matthieu Moy [off-list ref] writes:

-	if (pos < 0)
-		pos = -pos - 1;
-	ce = active_cache[pos];
-	if (ce_namelen(ce) == namelen &&
-	    !memcmp(ce->name, filename, namelen))
+	if (pos >= 0) {
+		ce = active_cache[pos];

A positive return value of cache_name_pos() is "I found a merged entry
with that name at this index" while a negative is "I would insert at this
index if you give me a merged entry with that name".

The latter is what the name comparison logic is about.  The caller asked
for filename, and the return value may point at an existing entry (in
which case you do not even need to memcmp(), but it doesn't hurt and
simplifies the code).  The nagative one with compensation could be
pointing at an unrelated entry, or an unmerged entry with filename you
asked, which sorts higher than a merged entry with the same name.