Re: [PATCH v3 06/12] cachefiles: add consistency check for copen/cread

[Jingbo Xu]

On 5/22/24 7:43 PM, libaokun@xxxxxxxxxxxxxxx wrote:
> From: Baokun Li <libaokun1@xxxxxxxxxx>
> 
> This prevents malicious processes from completing random copen/cread
> requests and crashing the system. Added checks are listed below:
> 
>   * Generic, copen can only complete open requests, and cread can only
>     complete read requests.
>   * For copen, ondemand_id must not be 0, because this indicates that the
>     request has not been read by the daemon.
>   * For cread, the object corresponding to fd and req should be the same.
> 
> Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
> Acked-by: Jeff Layton <jlayton@xxxxxxxxxx>
> ---
>  fs/cachefiles/ondemand.c | 27 ++++++++++++++++++++-------
>  1 file changed, 20 insertions(+), 7 deletions(-)
> 
> diff --git a/fs/cachefiles/ondemand.c b/fs/cachefiles/ondemand.c
> index bb94ef6a6f61..898fab68332b 100644
> --- a/fs/cachefiles/ondemand.c
> +++ b/fs/cachefiles/ondemand.c
> @@ -82,12 +82,12 @@ static loff_t cachefiles_ondemand_fd_llseek(struct file *filp, loff_t pos,
>  }
>  
>  static long cachefiles_ondemand_fd_ioctl(struct file *filp, unsigned int ioctl,
> -					 unsigned long arg)
> +					 unsigned long id)
>  {
>  	struct cachefiles_object *object = filp->private_data;
>  	struct cachefiles_cache *cache = object->volume->cache;
>  	struct cachefiles_req *req;
> -	unsigned long id;
> +	XA_STATE(xas, &cache->reqs, id);
>  
>  	if (ioctl != CACHEFILES_IOC_READ_COMPLETE)
>  		return -EINVAL;
> @@ -95,10 +95,15 @@ static long cachefiles_ondemand_fd_ioctl(struct file *filp, unsigned int ioctl,
>  	if (!test_bit(CACHEFILES_ONDEMAND_MODE, &cache->flags))
>  		return -EOPNOTSUPP;
>  
> -	id = arg;
> -	req = xa_erase(&cache->reqs, id);
> -	if (!req)
> +	xa_lock(&cache->reqs);
> +	req = xas_load(&xas);
> +	if (!req || req->msg.opcode != CACHEFILES_OP_READ ||
> +	    req->object != object) {
> +		xa_unlock(&cache->reqs);
>  		return -EINVAL;
> +	}
> +	xas_store(&xas, NULL);
> +	xa_unlock(&cache->reqs);
>  
>  	trace_cachefiles_ondemand_cread(object, id);
>  	complete(&req->done);
> @@ -126,6 +131,7 @@ int cachefiles_ondemand_copen(struct cachefiles_cache *cache, char *args)
>  	unsigned long id;
>  	long size;
>  	int ret;
> +	XA_STATE(xas, &cache->reqs, 0);
>  
>  	if (!test_bit(CACHEFILES_ONDEMAND_MODE, &cache->flags))
>  		return -EOPNOTSUPP;
> @@ -149,9 +155,16 @@ int cachefiles_ondemand_copen(struct cachefiles_cache *cache, char *args)
>  	if (ret)
>  		return ret;
>  
> -	req = xa_erase(&cache->reqs, id);
> -	if (!req)
> +	xa_lock(&cache->reqs);
> +	xas.xa_index = id;
> +	req = xas_load(&xas);
> +	if (!req || req->msg.opcode != CACHEFILES_OP_OPEN ||
> +	    !req->object->ondemand->ondemand_id) {

For a valid opened object, I think ondemand_id shall > 0.  When the
copen is for the object which is in the reopening state, ondemand_id can
be CACHEFILES_ONDEMAND_ID_CLOSED (actually -1)?

Otherwise looks good to me.


-- 
Thanks,
Jingbo