linux-kernel - Re: [PATCH v4] ksmbd: fix possible memory leak in smb2

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Date:   Wed, 15 Feb 2023 10:04:48 +0900
From:   Namjae Jeon <linkinjeon@...nel.org>
To:     Hangyu Hua <hbh25y@...il.com>
Cc:     sfrench@...ba.org, senozhatsky@...omium.org, tom@...pey.com,
        hyc.lee@...il.com, lsahlber@...hat.com, linux-cifs@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] ksmbd: fix possible memory leak in smb2_lock()

2023-02-14 15:36 GMT+09:00, Hangyu Hua <hbh25y@...il.com>:
> argv needs to be free when setup_async_work fails or when the current
> process is woken up.
>
> Fixes: e2f34481b24d ("cifsd: add server-side procedures for SMB3")
> Signed-off-by: Hangyu Hua <hbh25y@...il.com>
> ---
>
> v2: avoid NULL pointer dereference in set_close_state_blocked_works()
> v3: avoid race condition between smb2_lock() and smb2_cancel()
> v4: use another way to avoid race condition
>
>  fs/ksmbd/smb2pdu.c   | 20 +++++++++++++-------
>  fs/ksmbd/vfs_cache.c |  2 ++
>  2 files changed, 15 insertions(+), 7 deletions(-)
>
> diff --git a/fs/ksmbd/smb2pdu.c b/fs/ksmbd/smb2pdu.c
> index d681f91947d9..1b517d3ca2ef 100644
> --- a/fs/ksmbd/smb2pdu.c
> +++ b/fs/ksmbd/smb2pdu.c
> @@ -6666,7 +6666,8 @@ int smb2_cancel(struct ksmbd_work *work)
>  				    "smb2 with AsyncId %llu cancelled command = 0x%x\n",
>  				    le64_to_cpu(hdr->Id.AsyncId),
>  				    le16_to_cpu(chdr->Command));
> -			cancel_work = iter;
> +			if (iter->cancel_fn)
> +				cancel_work = iter;
You have freed ->cancel_argv in smb2_lock().  Wouldn't this cause UAF
issue the below?

        if (cancel_work) {
                cancel_work->state = KSMBD_WORK_CANCELLED;
                if (cancel_work->cancel_fn)
                        cancel_work->cancel_fn(cancel_work->cancel_argv);
        }
>  			break;
>  		}
>  		spin_unlock(&conn->request_lock);
> @@ -7050,6 +7051,7 @@ int smb2_lock(struct ksmbd_work *work)
>  						      smb2_remove_blocked_lock,
>  						      argv);
>  				if (rc) {
> +					kfree(argv);
>  					err = -ENOMEM;
>  					goto out;
>  				}
> @@ -7061,6 +7063,16 @@ int smb2_lock(struct ksmbd_work *work)
>
>  				ksmbd_vfs_posix_lock_wait(flock);
>
> +				spin_lock(&work->conn->request_lock);
> +				spin_lock(&fp->f_lock);
> +				if (work->state != KSMBD_WORK_CLOSED) {
I think that this check is not needed if we don't delete entry in
set_close_state_blocked_works().
> +					list_del(&work->fp_entry);
> +					work->cancel_fn = NULL;
> +					kfree(argv);
> +				}
> +				spin_unlock(&fp->f_lock);
> +				spin_unlock(&work->conn->request_lock);
> +
>  				if (work->state != KSMBD_WORK_ACTIVE) {
>  					list_del(&smb_lock->llist);
>  					spin_lock(&work->conn->llist_lock);
> @@ -7069,9 +7081,6 @@ int smb2_lock(struct ksmbd_work *work)
>  					locks_free_lock(flock);
>
>  					if (work->state == KSMBD_WORK_CANCELLED) {
> -						spin_lock(&fp->f_lock);
> -						list_del(&work->fp_entry);
> -						spin_unlock(&fp->f_lock);
>  						rsp->hdr.Status =
>  							STATUS_CANCELLED;
>  						kfree(smb_lock);
> @@ -7093,9 +7102,6 @@ int smb2_lock(struct ksmbd_work *work)
>  				list_del(&smb_lock->clist);
>  				spin_unlock(&work->conn->llist_lock);
>
> -				spin_lock(&fp->f_lock);
> -				list_del(&work->fp_entry);
> -				spin_unlock(&fp->f_lock);
>  				goto retry;
>  			} else if (!rc) {
>  				spin_lock(&work->conn->llist_lock);
> diff --git a/fs/ksmbd/vfs_cache.c b/fs/ksmbd/vfs_cache.c
> index da9163b00350..761a8aa540ce 100644
> --- a/fs/ksmbd/vfs_cache.c
> +++ b/fs/ksmbd/vfs_cache.c
> @@ -372,6 +372,8 @@ static void set_close_state_blocked_works(struct
> ksmbd_file *fp)
>  		list_del(&cancel_work->fp_entry);
>  		cancel_work->state = KSMBD_WORK_CLOSED;
>  		cancel_work->cancel_fn(cancel_work->cancel_argv);
> +		cancel_work->cancel_fn = NULL;
> +		kfree(cancel_work->cancel_argv);
If we remove list_del, we don't need to do them here ? and we can
change _safe version to list_for_each().
>  	}
>  	spin_unlock(&fp->f_lock);
>  }
> --
> 2.34.1
>
>