Re: [PATCH 1/1] NFSD: fix use-after-free in __nfs42_ssc_open()

dai.ngo
2022-12-12T13:57:17Z

On 12/12/22 5:40 AM, Jeff Layton wrote:
> On Mon, 2022-12-12 at 05:34 -0800, dai.ngo@oracle.com wrote:
>> On 12/12/22 4:22 AM, Jeff Layton wrote:
>>> On Sun, 2022-12-11 at 11:22 -0800, Dai Ngo wrote:
>>>> Problem caused by source's vfsmount being unmounted but remains
>>>> on the delayed unmount list. This happens when nfs42_ssc_open()
>>>> return errors.
>>>> Fixed by removing nfsd4_interssc_connect(), leave the vfsmount
>>>> for the laundromat to unmount when idle time expires.
>>>>
>>>> Reported-by: Xingyuan Mo <hdthky0@gmail.com>
>>>> Signed-off-by: Dai Ngo <dai.ngo@oracle.com>
>>>> ---
>>>> fs/nfsd/nfs4proc.c | 23 +++++++----------------
>>>> 1 file changed, 7 insertions(+), 16 deletions(-)
>>>>
>>>> diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
>>>> index 8beb2bc4c328..756e42cf0d01 100644
>>>> --- a/fs/nfsd/nfs4proc.c
>>>> +++ b/fs/nfsd/nfs4proc.c
>>>> @@ -1463,13 +1463,6 @@ nfsd4_interssc_connect(struct nl4_server *nss, struct svc_rqst *rqstp,
>>>> return status;
>>>> }
>>>>
>>>> -static void
>>>> -nfsd4_interssc_disconnect(struct vfsmount *ss_mnt)
>>>> -{
>>>> - nfs_do_sb_deactive(ss_mnt->mnt_sb);
>>>> - mntput(ss_mnt);
>>>> -}
>>>> -
>>>> /*
>>>> * Verify COPY destination stateid.
>>>> *
>>>> @@ -1572,11 +1565,6 @@ nfsd4_cleanup_inter_ssc(struct vfsmount *ss_mnt, struct file *filp,
>>>> {
>>>> }
>>>>
>>>> -static void
>>>> -nfsd4_interssc_disconnect(struct vfsmount *ss_mnt)
>>>> -{
>>>> -}
>>>> -
>>>> static struct file *nfs42_ssc_open(struct vfsmount *ss_mnt,
>>>> struct nfs_fh *src_fh,
>>>> nfs4_stateid *stateid)
>>>> @@ -1762,7 +1750,8 @@ static int nfsd4_do_async_copy(void *data)
>>>> struct file *filp;
>>>>
>>>> filp = nfs42_ssc_open(copy->ss_mnt, &copy->c_fh,
>>>> - &copy->stateid);
>>>> + &copy->stateid);
>>>> +
>>>> if (IS_ERR(filp)) {
>>>> switch (PTR_ERR(filp)) {
>>>> case -EBADF:
>>>> @@ -1771,7 +1760,7 @@ static int nfsd4_do_async_copy(void *data)
>>>> default:
>>>> nfserr = nfserr_offload_denied;
>>>> }
>>>> - nfsd4_interssc_disconnect(copy->ss_mnt);
>>>> + /* ss_mnt will be unmounted by the laundromat */
>>>> goto do_callback;
>>>> }
>>>> nfserr = nfsd4_do_copy(copy, filp, copy->nf_dst->nf_file,
>>>> @@ -1852,8 +1841,10 @@ nfsd4_copy(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
>>>> if (async_copy)
>>>> cleanup_async_copy(async_copy);
>>>> status = nfserrno(-ENOMEM);
>>>> - if (nfsd4_ssc_is_inter(copy))
>>>> - nfsd4_interssc_disconnect(copy->ss_mnt);
>>>> + /*
>>>> + * source's vfsmount of inter-copy will be unmounted
>>>> + * by the laundromat
>>>> + */
>>>> goto out;
>>>> }
>>>>
>>> This looks reasonable at first glance, but I have some concerns with the
>>> refcounting around ss_mnt elsewhere in this code. nfsd4_ssc_setup_dul
>>> looks for an existing connection and bumps the ni->nsui_refcnt if it
>>> finds one.
>>>
>>> But then later, nfsd4_cleanup_inter_ssc has a couple of cases where it
>>> just does a bare mntput:
>>>
>>> if (!nn) {
>>> mntput(ss_mnt);
>>> return;
>>> }
>>> ...
>>> if (!found) {
>>> mntput(ss_mnt);
>>> return;
>>> }
>>>
>>> The first one looks bogus. Can net_generic return NULL? If so how, and
>>> why is it not a problem elsewhere in the kernel?
>> it looks like net_generic can not fail, no where else check for NULL
>> so I will remove this check.
>>
>>> For the second case, if the ni is no longer on the list, where did the
>>> extra ss_mnt reference come from? Maybe that should be a WARN_ON or
>>> BUG_ON?
>> if ni is not found on the list then it's a bug somewhere so I will add
>> a BUG_ON on this.
>>
> Probably better to just WARN_ON and let any references leak in that
> case. A BUG_ON implies a panic in some environments, and it's best to
> avoid that unless there really is no choice.

ok, thanks Jeff!

-Dai