linux-kernel - Re: [PATCH 2/3] ceph: fix use-after-free in ceph

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Message-ID: <87h78co4g9.fsf@brahms.olymp>
Date:   Sat, 05 Mar 2022 14:32:22 +0000
From:   Luís Henriques <lhenriques@...e.de>
To:     Xiubo Li <xiubli@...hat.com>
Cc:     Jeff Layton <jlayton@...nel.org>,
        Ilya Dryomov <idryomov@...il.com>, ceph-devel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] ceph: fix use-after-free in ceph_readdir

Xiubo Li <xiubli@...hat.com> writes:

> On 3/5/22 2:20 AM, Jeff Layton wrote:
>> On Fri, 2022-03-04 at 16:14 +0000, Luís 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: Luís Henriques <lhenriques@...e.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.

Ok, cool.  This definitely proofs that my local branch wasn't updated :-)

(I really need to get rid of this mails/patches backlog.)

Cheers,
-- 
Luís