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Subject: Re: [PATCH v3] SUNRPC/cache: Fix unsafe traverse caused double-free
 in cache_purge
From:   Chuck Lever <chuck.lever@oracle.com>
In-Reply-To: <25dcf75e-65b1-b6e8-1fe5-81a193ed4189@linux.alibaba.com>
Date:   Sun, 5 Apr 2020 14:35:13 -0400
Cc:     Bruce Fields <bfields@fieldses.org>, Neil Brown <neilb@suse.de>,
        Sasha Levin <sashal@kernel.org>,
        Linux NFS Mailing List <linux-nfs@vger.kernel.org>
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Message-Id: <93CF97D8-1E4B-4310-9C51-9D373424D0BF@oracle.com>
References: <4568a7cf87f110b8e59fda6f53fda34c550ab403.1586108200.git.wuyihao@linux.alibaba.com>
 <e0dd0339-a15e-814d-ac5a-5f51bc15d73c@linux.alibaba.com>
 <0308EB8A-A8B7-412C-8F93-A444DE47CB1D@oracle.com>
 <25dcf75e-65b1-b6e8-1fe5-81a193ed4189@linux.alibaba.com>
To:     Yihao Wu <wuyihao@linux.alibaba.com>
Sender: linux-nfs-owner@vger.kernel.org
Precedence: bulk


> On Apr 5, 2020, at 2:31 PM, Yihao Wu <wuyihao@linux.alibaba.com> =
wrote:
>=20
>>> net/sunrpc/cache.c | 4 +++-
>>> 1 file changed, 3 insertions(+), 1 deletion(-)
>>>=20
>>> 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 =3D 0; i < detail->hash_size; i++) {
>>> 		head =3D &detail->hash_table[i];
>>> -		hlist_for_each_entry_safe(ch, tmp, head, cache_list) {
>>=20
>> If review/testing shows you need to respin this patch, I note that =
"tmp" is
>> now unused and should be removed. I've pulled v3 into my testing =
branch and
>> made that minor change. Thanks!
>>=20
>>=20
>>> +		while (!hlist_empty(head)) {
>>> +			ch =3D 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);
>>> --=20
>>> 2.20.1.2432.ga663e714
>>=20
>> --
>> Chuck Lever
>>=20
>>=20
>=20
> Thanks a lot, Chuck!
>=20
> If it needs further changes by me, I'll fix the unused 'tmp' along =
with them.
>=20
> BTW, if you and Neil think it's proper to add Signed-off-by Neil too =
later,
> please do, since the bug fix owes to Neil's idea :-)

Actually a "Suggested-by:" tag is appropriate for attribution. I'll add:

Suggested-by: NeilBrown <neilb@suse.de>

to what I have in my tree.


--
Chuck Lever