SUNRPC/cache: Fix unsafe traverse caused double-free in cache_purge

Deleting list entry within hlist_for_each_entry_safe is not safe unless
next pointer (tmp) is protected too. It's not, because once hash_lock
is released, cache_clean may delete the entry that tmp points to. Then
cache_purge can walk to a deleted entry and tries to double free it.

Fix this bug by holding only the deleted entry's reference.

Suggested-by: NeilBrown <neilb@suse.de>
Signed-off-by: Yihao Wu <wuyihao@linux.alibaba.com>
Reviewed-by: NeilBrown <neilb@suse.de>
[ cel: removed unused variable ]
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
index af0ddd28b081cd166b4dc4339bfdcc0f548a6256..baef5ee43dbbdb3fbc9b5bdf780a585e8d877404 100644 (file)
--- a/net/sunrpc/cache.c
+++ b/net/sunrpc/cache.c
@@ -529,7 +529,6 @@ void cache_purge(struct cache_detail *detail)
 {
        struct cache_head *ch = NULL;
        struct hlist_head *head = NULL;
-       struct hlist_node *tmp = NULL;
        int i = 0;
 
        spin_lock(&detail->hash_lock);
@@ -541,7 +540,9 @@ void cache_purge(struct cache_detail *detail)
        dprintk("RPC: %d entries in %s cache\n", detail->entries, detail->name);
        for (i = 0; i < detail->hash_size; i++) {
                head = &detail->hash_table[i];
-               hlist_for_each_entry_safe(ch, tmp, head, cache_list) {
+               while (!hlist_empty(head)) {
+                       ch = hlist_entry(head->first, struct cache_head,
+                                        cache_list);
                        sunrpc_begin_cache_remove_entry(ch, detail);
                        spin_unlock(&detail->hash_lock);
                        sunrpc_end_cache_remove_entry(ch, detail);