In the Linux kernel, the following vulnerability has been resolved:net: ethernet: oa_tc6: fix tx skb race condition between reference pointersThere are two skb pointers to manage tx skb's enqueued from n/w stack.
waiting_tx_skb pointer points to the tx skb which needs to be processed
and ongoing_tx_skb pointer points to the tx skb which is being processed.SPI thread prepares the tx data chunks from the tx skb pointed by the
ongoing_tx_skb pointer. When the tx skb pointed by the ongoing_tx_skb is
processed, the tx skb pointed by the waiting_tx_skb is assigned to
ongoing_tx_skb and the waiting_tx_skb pointer is assigned with NULL.
Whenever there is a new tx skb from n/w stack, it will be assigned to
waiting_tx_skb pointer if it is NULL. Enqueuing and processing of a tx skb
handled in two different threads.Consider a scenario where the SPI thread processed an ongoing_tx_skb and
it moves next tx skb from waiting_tx_skb pointer to ongoing_tx_skb pointer
without doing any NULL check. At this time, if the waiting_tx_skb pointer
is NULL then ongoing_tx_skb pointer is also assigned with NULL. After
that, if a new tx skb is assigned to waiting_tx_skb pointer by the n/w
stack and there is a chance to overwrite the tx skb pointer with NULL in
the SPI thread. Finally one of the tx skb will be left as unhandled,
resulting packet missing and memory leak.Consider the below scenario where the TXC reported from the previous
transfer is 10 and ongoing_tx_skb holds an tx ethernet frame which can be
transported in 20 TXCs and waiting_tx_skb is still NULL.
  tx_credits = 10; /* 21 are filled in the previous transfer */
  ongoing_tx_skb = 20;
  waiting_tx_skb = NULL; /* Still NULL */So, (tc6->ongoing_tx_skb || tc6->waiting_tx_skb) becomes true.After oa_tc6_prepare_spi_tx_buf_for_tx_skbs()
  ongoing_tx_skb = 10;
  waiting_tx_skb = NULL; /* Still NULL */Perform SPI transfer.Process SPI rx buffer to get the TXC from footers.Now let's assume previously filled 21 TXCs are freed so we are good to
transport the next remaining 10 tx chunks from ongoing_tx_skb.
  tx_credits = 21;
  ongoing_tx_skb = 10;
  waiting_tx_skb = NULL;So, (tc6->ongoing_tx_skb || tc6->waiting_tx_skb) becomes true again.In the oa_tc6_prepare_spi_tx_buf_for_tx_skbs()
  ongoing_tx_skb = NULL;
  waiting_tx_skb = NULL;Now the below bad case might happen,Thread1 (oa_tc6_start_xmit)	Thread2 (oa_tc6_spi_thread_handler)if waiting_tx_skb is NULL
  			- if ongoing_tx_skb is NULL
  			- ongoing_tx_skb = waiting_tx_skbwaiting_tx_skb = skb
  			- waiting_tx_skb = NULL
  			...
  			- ongoing_tx_skb = NULLif waiting_tx_skb is NULLwaiting_tx_skb = skbTo overcome the above issue, protect the moving of tx skb reference from
waiting_tx_skb pointer to ongoing_tx_skb pointer and assigning new tx skb
to waiting_tx_skb pointer, so that the other thread can't access the
waiting_tx_skb pointer until the current thread completes moving the tx
skb reference safely.