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autofs-5.1.7 - refactor lookup_prune_one_cache() a bit
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From: Ian Kent <raven@themaw.net>
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Coverity: use: Using an unreliable value of "me" inside the second locked
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section.
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Change lookup_prune_one_cache() a little, move the location the next
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key is set (before releasing the lock) and add a comment explaining
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why we don't care about the side effects of the read lock release/
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write lock aquire/write lock release/read lock reaquire.
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Signed-off-by: Ian Kent <raven@themaw.net>
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---
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CHANGELOG | 1 +
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daemon/lookup.c | 20 +++++++++++++++++++-
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2 files changed, 20 insertions(+), 1 deletion(-)
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diff --git a/CHANGELOG b/CHANGELOG
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index 81461978..b79aebc8 100644
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--- a/CHANGELOG
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+++ b/CHANGELOG
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@@ -63,6 +63,7 @@
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- fix arg not used in error print.
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- fix missing lock release in mount_subtree().
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- fix double free in parse_mapent().
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+- refactor lookup_prune_one_cache() a bit.
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25/01/2021 autofs-5.1.7
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- make bind mounts propagation slave by default.
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diff --git a/daemon/lookup.c b/daemon/lookup.c
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index 32dbc24d..3e9722e4 100644
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--- a/daemon/lookup.c
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+++ b/daemon/lookup.c
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@@ -1375,7 +1375,6 @@ void lookup_prune_one_cache(struct autofs_point *ap, struct mapent_cache *mc, ti
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}
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key = strdup(me->key);
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- me = cache_enumerate(mc, me);
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/* Don't consider any entries with a wildcard */
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if (!key || strchr(key, '*')) {
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if (key)
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@@ -1422,6 +1421,7 @@ void lookup_prune_one_cache(struct autofs_point *ap, struct mapent_cache *mc, ti
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if (valid)
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cache_unlock(valid->mc);
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+ me = cache_enumerate(mc, me);
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if (me)
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next_key = strdup(me->key);
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@@ -1456,6 +1456,24 @@ void lookup_prune_one_cache(struct autofs_point *ap, struct mapent_cache *mc, ti
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next:
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cache_readlock(mc);
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if (next_key) {
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+ /* The lock release and reaquire above can mean
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+ * a number of things could happen.
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+ *
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+ * First, mapents could be added between the
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+ * current mapent and the mapent of next_key.
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+ * Don't care about that because there's no
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+ * need to prune newly added entries.
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+ *
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+ * Second, the next mapent data could have
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+ * changed. Don't care about that either since
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+ * we are looking to prune stale map entries
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+ * and don't care when they become stale.
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+ *
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+ * Finally, the mapent of next_key could have
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+ * gone away. Again don't care about this either,
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+ * the loop will exit prematurely so just wait
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+ * until the next prune and try again.
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+ */
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me = cache_lookup_distinct(mc, next_key);
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free(next_key);
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}
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