autofs-5.1.4 - fix update_negative_cache() map source usage

From: Ian Kent <raven@themaw.net>

File map sources can be either plain text or executable.

When the map path is specified without a type (eg. when a
full path is used) an instance map source is used and the
original map is left unchanged.

But update_negative_cache() fails to take this into account
causing it to update the wrong map cache.

When a map reload is done the map entry appears to not exist
so the new map entry is added.

This could go unnoticed except that, after a map read, the
map entry cache cleans stale map entries and the existence
of this negative entry causes the new map entry to be deleted
and map lookups continue to fail.

In hindsite the use of an instance map source for this is
probably uneccessary but changing it will be risky so, for
now, just make update_negative_cache() use the correct map.

Signed-off-by: Ian Kent <raven@themaw.net>
---
 CHANGELOG       |    1 +
 daemon/lookup.c |   38 ++++++++++++++++++++++++++++++++++++--
 2 files changed, 37 insertions(+), 2 deletions(-)

diff --git a/CHANGELOG b/CHANGELOG
index c39aa0e5..70e043ee 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -31,6 +31,7 @@ xx/xx/2018 autofs-5.1.5
 - use defines for expire type.
 - enable SIGUSR2 handling in rpm spec file.
 - fix age setting at startup.
+- fix update_negative_cache() map source usage.
 
 19/12/2017 autofs-5.1.4
 - fix spec file url.
diff --git a/daemon/lookup.c b/daemon/lookup.c
index 6a722b3b..418f01cb 100644
--- a/daemon/lookup.c
+++ b/daemon/lookup.c
@@ -1100,6 +1100,37 @@ static enum nsswitch_status lookup_map_name(struct nss_source *this,
 	return result;
 }
 
+static struct map_source *lookup_get_map_source(struct master_mapent *entry)
+{
+	struct map_source *map = entry->maps;
+	struct stat st;
+	char *type;
+
+	if (map->type || *map->argv[0] != '/')
+		return map;
+
+	if (*(map->argv[0] + 1) == '/')
+		return map;
+
+	if (stat(map->argv[0], &st) == -1)
+		return NULL;
+
+	if (!S_ISREG(st.st_mode))
+		return NULL;
+
+	if (st.st_mode & __S_IEXEC)
+		type = "program";
+	else
+		type = "file";
+
+	/* This is a file source with a path starting with "/".
+	 * But file maps can be either plain text or executable
+	 * so they use a map instance and the actual map source
+	 * remains untouched.
+	 */
+	return master_find_source_instance(map, type, map->format, 0, NULL);
+}
+
 static void update_negative_cache(struct autofs_point *ap, struct map_source *source, const char *name)
 {
 	struct master_mapent *entry = ap->entry;
@@ -1133,11 +1164,14 @@ static void update_negative_cache(struct autofs_point *ap, struct map_source *so
 			logmsg("key \"%s\" not found in map source(s).", name);
 		}
 
-		/* Doesn't exist in any source, just add it somewhere */
+		/* Doesn't exist in any source, just add it somewhere.
+		 * Also take care to use the same map source used by
+		 * map reads and key lookups for the update.
+		 */
 		if (source)
 			map = source;
 		else
-			map = entry->maps;
+			map = lookup_get_map_source(entry);
 		if (map) {
 			time_t now = monotonic_time(NULL);
 			int rv = CHE_FAIL;