Patch "ibmvnic: Add tx check to prevent skb leak" has been added to the 6.6-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    ibmvnic: Add tx check to prevent skb leak

to the 6.6-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     ibmvnic-add-tx-check-to-prevent-skb-leak.patch
and it can be found in the queue-6.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 2b87ccbd3c872618302b1d2560c7bfedb7e5937e
Author: Nick Child <nnac123@xxxxxxxxxxxxx>
Date:   Thu Jun 20 10:23:11 2024 -0500

    ibmvnic: Add tx check to prevent skb leak
    
    [ Upstream commit 0983d288caf984de0202c66641577b739caad561 ]
    
    Below is a summary of how the driver stores a reference to an skb during
    transmit:
        tx_buff[free_map[consumer_index]]->skb = new_skb;
        free_map[consumer_index] = IBMVNIC_INVALID_MAP;
        consumer_index ++;
    Where variable data looks like this:
        free_map == [4, IBMVNIC_INVALID_MAP, IBMVNIC_INVALID_MAP, 0, 3]
                                                    consumer_index^
        tx_buff == [skb=null, skb=<ptr>, skb=<ptr>, skb=null, skb=null]
    
    The driver has checks to ensure that free_map[consumer_index] pointed to
    a valid index but there was no check to ensure that this index pointed
    to an unused/null skb address. So, if, by some chance, our free_map and
    tx_buff lists become out of sync then we were previously risking an
    skb memory leak. This could then cause tcp congestion control to stop
    sending packets, eventually leading to ETIMEDOUT.
    
    Therefore, add a conditional to ensure that the skb address is null. If
    not then warn the user (because this is still a bug that should be
    patched) and free the old pointer to prevent memleak/tcp problems.
    
    Signed-off-by: Nick Child <nnac123@xxxxxxxxxxxxx>
    Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/net/ethernet/ibm/ibmvnic.c b/drivers/net/ethernet/ibm/ibmvnic.c
index ca21e55335b23..61685c3053ad7 100644
--- a/drivers/net/ethernet/ibm/ibmvnic.c
+++ b/drivers/net/ethernet/ibm/ibmvnic.c
@@ -2478,6 +2478,18 @@ static netdev_tx_t ibmvnic_xmit(struct sk_buff *skb, struct net_device *netdev)
 	    (tx_pool->consumer_index + 1) % tx_pool->num_buffers;
 
 	tx_buff = &tx_pool->tx_buff[bufidx];
+
+	/* Sanity checks on our free map to make sure it points to an index
+	 * that is not being occupied by another skb. If skb memory is
+	 * not freed then we see congestion control kick in and halt tx.
+	 */
+	if (unlikely(tx_buff->skb)) {
+		dev_warn_ratelimited(dev, "TX free map points to untracked skb (%s %d idx=%d)\n",
+				     skb_is_gso(skb) ? "tso_pool" : "tx_pool",
+				     queue_num, bufidx);
+		dev_kfree_skb_any(tx_buff->skb);
+	}
+
 	tx_buff->skb = skb;
 	tx_buff->index = bufidx;
 	tx_buff->pool_index = queue_num;