Patch "dmaengine: fix NULL pointer in channel unregistration function" has been added to the 5.15-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

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

    dmaengine: fix NULL pointer in channel unregistration function

to the 5.15-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:
     dmaengine-fix-null-pointer-in-channel-unregistration.patch
and it can be found in the queue-5.15 subdirectory.

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



commit 96cb3f4144b769a8f2be6f70258a0fee4d2ca9e2
Author: Amelie Delaunay <amelie.delaunay@xxxxxxxxxxx>
Date:   Wed Dec 13 17:04:52 2023 +0100

    dmaengine: fix NULL pointer in channel unregistration function
    
    [ Upstream commit f5c24d94512f1b288262beda4d3dcb9629222fc7 ]
    
    __dma_async_device_channel_register() can fail. In case of failure,
    chan->local is freed (with free_percpu()), and chan->local is nullified.
    When dma_async_device_unregister() is called (because of managed API or
    intentionally by DMA controller driver), channels are unconditionally
    unregistered, leading to this NULL pointer:
    [    1.318693] Unable to handle kernel NULL pointer dereference at virtual address 00000000000000d0
    [...]
    [    1.484499] Call trace:
    [    1.486930]  device_del+0x40/0x394
    [    1.490314]  device_unregister+0x20/0x7c
    [    1.494220]  __dma_async_device_channel_unregister+0x68/0xc0
    
    Look at dma_async_device_register() function error path, channel device
    unregistration is done only if chan->local is not NULL.
    
    Then add the same condition at the beginning of
    __dma_async_device_channel_unregister() function, to avoid NULL pointer
    issue whatever the API used to reach this function.
    
    Fixes: d2fb0a043838 ("dmaengine: break out channel registration")
    Signed-off-by: Amelie Delaunay <amelie.delaunay@xxxxxxxxxxx>
    Reviewed-by: Dave Jiang <dave.jiang@xxxxxxxxx>
    Link: https://lore.kernel.org/r/20231213160452.2598073-1-amelie.delaunay@xxxxxxxxxxx
    Signed-off-by: Vinod Koul <vkoul@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
index 4ec7bb58c195..9559ebd61f3b 100644
--- a/drivers/dma/dmaengine.c
+++ b/drivers/dma/dmaengine.c
@@ -1108,6 +1108,9 @@ EXPORT_SYMBOL_GPL(dma_async_device_channel_register);
 static void __dma_async_device_channel_unregister(struct dma_device *device,
 						  struct dma_chan *chan)
 {
+	if (chan->local == NULL)
+		return;
+
 	WARN_ONCE(!device->device_release && chan->client_count,
 		  "%s called while %d clients hold a reference\n",
 		  __func__, chan->client_count);