From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	Juan Li <lijuan@linux.spacemit.com>,
	Guodong Xu <guodong@riscstar.com>,
	Vinod Koul <vkoul@kernel.org>,
	Wenshan Lan <jetlan9@163.com>
Subject: [PATCH 6.1 456/481] dmaengine: mmp_pdma: Fix race condition in mmp_pdma_residue()
Date: Mon, 23 Mar 2026 14:47:18 +0100
Message-ID: <20260323134536.321763681@linuxfoundation.org>
In-Reply-To: <20260323134525.256603107@linuxfoundation.org>
References: <20260323134525.256603107@linuxfoundation.org>
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6.1-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Guodong Xu <guodong@riscstar.com>

commit a143545855bc2c6e1330f6f57ae375ac44af00a7 upstream.

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>
[ Minor context conflict resolved. ]
Signed-off-by: Wenshan Lan <jetlan9@163.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/dma/mmp_pdma.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/drivers/dma/mmp_pdma.c
+++ b/drivers/dma/mmp_pdma.c
@@ -764,6 +764,7 @@ static unsigned int mmp_pdma_residue(str
 {
 	struct mmp_pdma_desc_sw *sw;
 	u32 curr, residue = 0;
+	unsigned long flags;
 	bool passed = false;
 	bool cyclic = chan->cyclic_first != NULL;
 
@@ -779,6 +780,8 @@ static unsigned int mmp_pdma_residue(str
 	else
 		curr = readl(chan->phy->base + DSADR(chan->phy->idx));
 
+	spin_lock_irqsave(&chan->desc_lock, flags);
+
 	list_for_each_entry(sw, &chan->chain_running, node) {
 		u32 start, end, len;
 
@@ -822,6 +825,7 @@ static unsigned int mmp_pdma_residue(str
 			continue;
 
 		if (sw->async_tx.cookie == cookie) {
+			spin_unlock_irqrestore(&chan->desc_lock, flags);
 			return residue;
 		} else {
 			residue = 0;
@@ -829,6 +833,8 @@ static unsigned int mmp_pdma_residue(str
 		}
 	}
 
+	spin_unlock_irqrestore(&chan->desc_lock, flags);
+
 	/* We should only get here in case of cyclic transactions */
 	return residue;
 }