[PATCH] util/qht: fix possible NULL pointer dereference in qht_bucket_remove_entry()

[gerben]

From: Denis Rastyogin <ger...@altlinux.org>

If b->pointers[i] is NULL on the first iteration and
prev has not yet been assigned (i.e., is still NULL),
calling qht_entry_move(orig, pos, prev, QHT_BUCKET_ENTRIES - 1)
can lead to a NULL pointer dereference.

The qht_debug_assert(prev) check does not prevent this issue
because QHT_DEBUG is currently disabled (the #define is commented out).

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Reported-by: Alexey Appolonov <ale...@altlinux.org>
Signed-off-by: Denis Rastyogin <ger...@altlinux.org>
---
 util/qht.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/util/qht.c b/util/qht.c
index 92c6b78759..cb7e367ebb 100644
--- a/util/qht.c
+++ b/util/qht.c
@@ -768,6 +768,9 @@ static inline void qht_bucket_remove_entry(struct 
qht_bucket *orig, int pos)
                 return qht_entry_move(orig, pos, b, i - 1);
             }
             qht_debug_assert(prev);
+            if (!prev) {
+                continue;
+            }
             return qht_entry_move(orig, pos, prev, QHT_BUCKET_ENTRIES - 1);
         }
         prev = b;
-- 
2.42.2