Received-SPF: pass (google.com: best guess record for domain of linux-nfs-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Subject: [PATCH v3] SUNRPC/cache: Fix unsafe traverse caused double-free in
 cache_purge
From:   Yihao Wu <wuyihao@linux.alibaba.com>
To:     "J . Bruce Fields" <bfields@fieldses.org>,
        Chuck Lever <chuck.lever@oracle.com>,
        NeilBrown <neilb@suse.de>, Sasha Levin <sashal@kernel.org>
Cc:     linux-nfs@vger.kernel.org
References: <4568a7cf87f110b8e59fda6f53fda34c550ab403.1586108200.git.wuyihao@linux.alibaba.com>
Message-ID: <e0dd0339-a15e-814d-ac5a-5f51bc15d73c@linux.alibaba.com>
Date:   Mon, 6 Apr 2020 01:57:22 +0800
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0)
 Gecko/20100101 Thunderbird/68.6.0
MIME-Version: 1.0
In-Reply-To: <4568a7cf87f110b8e59fda6f53fda34c550ab403.1586108200.git.wuyihao@linux.alibaba.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-nfs-owner@vger.kernel.org
Precedence: bulk

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.

Signed-off-by: Yihao Wu <wuyihao@linux.alibaba.com>
---
v1->v2: Use Neil's better solution
v2->v3: Fix a checkscript warning

 net/sunrpc/cache.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/sunrpc/cache.c b/net/sunrpc/cache.c
index af0ddd28b081..b445874e8e2f 100644
--- a/net/sunrpc/cache.c
+++ b/net/sunrpc/cache.c
@@ -541,7 +541,9 @@ 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);
-- 
2.20.1.2432.ga663e714