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Subject: Re: [PATCH 2/3] ceph: fix use-after-free in ceph_readdir
To:     Jeff Layton <jlayton@kernel.org>,
        =?UTF-8?Q?Lu=c3=ads_Henriques?= <lhenriques@suse.de>,
        Ilya Dryomov <idryomov@gmail.com>
Cc:     ceph-devel@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20220304161403.19295-1-lhenriques@suse.de>
 <20220304161403.19295-3-lhenriques@suse.de>
 <55c6363a0ef0dcca3e6a7c882783f5d47dbbbdc7.camel@kernel.org>
From:   Xiubo Li <xiubli@redhat.com>
Message-ID: <79cd6979-cb02-c0a3-a4e9-d66f65d78976@redhat.com>
Date:   Sat, 5 Mar 2022 20:43:04 +0800
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On 3/5/22 2:20 AM, Jeff Layton wrote:
> On Fri, 2022-03-04 at 16:14 +0000, Lu?s Henriques wrote:
>> After calling ceph_mdsc_put_request() on dfi->last_readdir, this field
>> should be set to NULL, otherwise we may end-up freeing it twince and get
>> the following splat:
>>
>>    refcount_t: underflow; use-after-free.
>>    WARNING: CPU: 0 PID: 229 at lib/refcount.c:28 refcount_warn_saturate+0xa6/0xf0
>>    ...
>>    Call Trace:
>>      <TASK>
>>      ceph_readdir+0xd35/0x1460 [ceph]
>>      ? _raw_spin_unlock+0x12/0x30
>>      ? preempt_count_add+0x73/0xa0
>>      ? _raw_spin_unlock+0x12/0x30
>>      ? __mark_inode_dirty+0x27c/0x3a0
>>      iterate_dir+0x7d/0x190
>>      __x64_sys_getdents64+0x80/0x120
>>      ? compat_fillonedir+0x160/0x160
>>      do_syscall_64+0x43/0x90
>>      entry_SYSCALL_64_after_hwframe+0x44/0xae
>>
>> Signed-off-by: Lu?s Henriques <lhenriques@suse.de>
>> ---
>>   fs/ceph/dir.c | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/fs/ceph/dir.c b/fs/ceph/dir.c
>> index 0bcb677d2199..934402f5e9e6 100644
>> --- a/fs/ceph/dir.c
>> +++ b/fs/ceph/dir.c
>> @@ -555,6 +555,7 @@ static int ceph_readdir(struct file *file, struct dir_context *ctx)
>>   			      le32_to_cpu(rde->inode.in->mode) >> 12)) {
>>   			dout("filldir stopping us...\n");
>>   			ceph_mdsc_put_request(dfi->last_readdir);
>> +			dfi->last_readdir = NULL;
>>   			err = 0;
>>   			goto out;
>>   		}
> I think Xiubo fixed this in the testing branch late yesterday. It should
> no longer be needed.

Right and I have sent a new version of my previous patch to remove the 
buggy code.

- Xiubo

> Thanks,