dmaengine: mmp_pdma: Fix race condition in mmp_pdma_residue()

Add proper locking in mmp_pdma_residue() to prevent use-after-free when
accessing descriptor list and descriptor contents.

The race occurs when multiple threads call tx_status() while the tasklet
on another CPU is freeing completed descriptors:

CPU 0                              CPU 1
-----                              -----
mmp_pdma_tx_status()
mmp_pdma_residue()
  -> NO LOCK held
     list_for_each_entry(sw, ..)
                                   DMA interrupt
                                   dma_do_tasklet()
                                     -> spin_lock(&desc_lock)
                                        list_move(sw->node, ...)
                                        spin_unlock(&desc_lock)
  |                                     dma_pool_free(sw) <- FREED!
  -> access sw->desc <- UAF!

This issue can be reproduced when running dmatest on the same channel with
multiple threads (threads_per_chan > 1).

Fix by protecting the chain_running list iteration and descriptor access
with the chan->desc_lock spinlock.

Signed-off-by: Juan Li <lijuan@linux.spacemit.com>
Signed-off-by: Guodong Xu <guodong@riscstar.com>
Link: https://patch.msgid.link/20251216-mmp-pdma-race-v1-1-976a224bb622@riscstar.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

diff --git a/drivers/dma/mmp_pdma.c b/drivers/dma/mmp_pdma.c
index 86661eb3cde1ff6d6d8f02b6f0d4142878b5a890..d12e729ee12c5688bc54ca312eaa4b9e3e1a83d4 100644 (file)
--- a/drivers/dma/mmp_pdma.c
+++ b/drivers/dma/mmp_pdma.c
@@ -928,6 +928,7 @@ static unsigned int mmp_pdma_residue(struct mmp_pdma_chan *chan,
 {
        struct mmp_pdma_desc_sw *sw;
        struct mmp_pdma_device *pdev = to_mmp_pdma_dev(chan->chan.device);
+       unsigned long flags;
        u64 curr;
        u32 residue = 0;
        bool passed = false;
@@ -945,6 +946,8 @@ static unsigned int mmp_pdma_residue(struct mmp_pdma_chan *chan,
        else
                curr = pdev->ops->read_src_addr(chan->phy);
 
+       spin_lock_irqsave(&chan->desc_lock, flags);
+
        list_for_each_entry(sw, &chan->chain_running, node) {
                u64 start, end;
                u32 len;
@@ -989,6 +992,7 @@ static unsigned int mmp_pdma_residue(struct mmp_pdma_chan *chan,
                        continue;
 
                if (sw->async_tx.cookie == cookie) {
+                       spin_unlock_irqrestore(&chan->desc_lock, flags);
                        return residue;
                } else {
                        residue = 0;
@@ -996,6 +1000,8 @@ static unsigned int mmp_pdma_residue(struct mmp_pdma_chan *chan,
                }
        }
 
+       spin_unlock_irqrestore(&chan->desc_lock, flags);
+
        /* We should only get here in case of cyclic transactions */
        return residue;
 }