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

dai.ngo
2022-12-12T13:34:52Z

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.

Thanks,
-Dai