• Valentine Fatiev's avatar
    IB/ipoib: Fix double free of skb in case of multicast traffic in CM mode · 1acba6a8
    Valentine Fatiev authored
    When connected mode is set, and we have connected and datagram traffic in
    parallel, ipoib might crash with double free of datagram skb.
    
    The current mechanism assumes that the order in the completion queue is
    the same as the order of sent packets for all QPs. Order is kept only for
    specific QP, in case of mixed UD and CM traffic we have few QPs (one UD and
    few CM's) in parallel.
    
    The problem:
    ----------------------------------------------------------
    
    Transmit queue:
    -----------------
    UD skb pointer kept in queue itself, CM skb kept in spearate queue and
    uses transmit queue as a placeholder to count the number of total
    transmitted packets.
    
    0   1   2   3   4  5  6  7  8   9  10  11 12 13 .........127
    ------------------------------------------------------------
    NL ud1 UD2 CM1 ud3 cm2 cm3 ud4 cm4 ud5 NL NL NL ...........
    ------------------------------------------------------------
        ^                                  ^
       tail                               head
    
    Completion queue (problematic scenario) - the order not the same as in
    the transmit queue:
    
      1  2  3  4  5  6  7  8  9
    ------------------------------------
     ud1 CM1 UD2 ud3 cm2 cm3 ud4 cm4 ud5
    ------------------------------------
    
    1. CM1 'wc' processing
       - skb freed in cm separate ring.
       - tx_tail of transmit queue increased although UD2 is not freed.
         Now driver assumes UD2 index is already freed and it could be used for
         new transmitted skb.
    
    0   1   2   3   4  5  6  7  8   9  10  11 12 13 .........127
    ------------------------------------------------------------
    NL NL  UD2 CM1 ud3 cm2 cm3 ud4 cm4 ud5 NL NL NL ...........
    ------------------------------------------------------------
            ^   ^                       ^
          (Bad)tail                    head
    (Bad - Could be used for new SKB)
    
    In this case (due to heavy load) UD2 skb pointer could be replaced by new
    transmitted packet UD_NEW, as the driver assumes its free.  At this point
    we will have to process two 'wc' with same index but we have only one
    pointer to free.
    
    During second attempt to free the same skb we will have NULL pointer
    exception.
    
    2. UD2 'wc' processing
       - skb freed according the index we got from 'wc', but it was already
         overwritten by mistake. So actually the skb that was released is the
         skb of the new transmitted packet and not the original one.
    
    3. UD_NEW 'wc' processing
       - attempt to free already freed skb. NUll pointer exception.
    
    The fix:
    -----------------------------------------------------------------------
    
    The fix is to stop using the UD ring as a placeholder for CM packets, the
    cyclic ring variables tx_head and tx_tail will manage the UD tx_ring, a
    new cyclic variables global_tx_head and global_tx_tail are introduced for
    managing and counting the overall outstanding sent packets, then the send
    queue will be stopped and waken based on these variables only.
    
    Note that no locking is needed since global_tx_head is updated in the xmit
    flow and global_tx_tail is updated in the NAPI flow only.  A previous
    attempt tried to use one variable to count the outstanding sent packets,
    but it did not work since xmit and NAPI flows can run at the same time and
    the counter will be updated wrongly. Thus, we use the same simple cyclic
    head and tail scheme that we have today for the UD tx_ring.
    
    Fixes: 2c104ea6 ("IB/ipoib: Get rid of the tx_outstanding variable in all modes")
    Link: https://lore.kernel.org/r/20200527134705.480068-1-leon@kernel.orgSigned-off-by: default avatarValentine Fatiev <valentinef@mellanox.com>
    Signed-off-by: default avatarAlaa Hleihel <alaa@mellanox.com>
    Signed-off-by: default avatarLeon Romanovsky <leonro@mellanox.com>
    Acked-by: default avatarDoug Ledford <dledford@redhat.com>
    Signed-off-by: default avatarJason Gunthorpe <jgg@mellanox.com>
    1acba6a8
ipoib_ib.c 33.6 KB