[PATCH v3 02/12] cachefiles: remove requests from xarray during flushing requests

[libaokun]

From: Baokun Li <libaokun1@xxxxxxxxxx>

Even with CACHEFILES_DEAD set, we can still read the requests, so in the
following concurrency the request may be used after it has been freed:

     mount  |   daemon_thread1    |    daemon_thread2
------------------------------------------------------------
 cachefiles_ondemand_init_object
  cachefiles_ondemand_send_req
   REQ_A = kzalloc(sizeof(*req) + data_len)
   wait_for_completion(&REQ_A->done)
            cachefiles_daemon_read
             cachefiles_ondemand_daemon_read
                                  // close dev fd
                                  cachefiles_flush_reqs
                                   complete(&REQ_A->done)
   kfree(REQ_A)
              xa_lock(&cache->reqs);
              cachefiles_ondemand_select_req
                req->msg.opcode != CACHEFILES_OP_READ
                // req use-after-free !!!
              xa_unlock(&cache->reqs);
                                   xa_destroy(&cache->reqs)

Hence remove requests from cache->reqs when flushing them to avoid
accessing freed requests.

Fixes: c8383054506c ("cachefiles: notify the user daemon when looking up cookie")
Signed-off-by: Baokun Li <libaokun1@xxxxxxxxxx>
Acked-by: Jeff Layton <jlayton@xxxxxxxxxx>
Reviewed-by: Jia Zhu <zhujia.zj@xxxxxxxxxxxxx>
Reviewed-by: Gao Xiang <hsiangkao@xxxxxxxxxxxxxxxxx>
Reviewed-by: Jingbo Xu <jefflexu@xxxxxxxxxxxxxxxxx>
---
 fs/cachefiles/daemon.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/cachefiles/daemon.c b/fs/cachefiles/daemon.c
index 6465e2574230..ccb7b707ea4b 100644
--- a/fs/cachefiles/daemon.c
+++ b/fs/cachefiles/daemon.c
@@ -159,6 +159,7 @@ static void cachefiles_flush_reqs(struct cachefiles_cache *cache)
 	xa_for_each(xa, index, req) {
 		req->error = -EIO;
 		complete(&req->done);
+		__xa_erase(xa, index);
 	}
 	xa_unlock(xa);
 
-- 
2.39.2