linux-kernel - Re: [PATCH] dmaengine: tegra-adma: Fix use-after-free

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Message-ID: <ovxny5nhgn2lnfq2bespxwzntkug7l7pwfwhrn47nc42nvtn2h@6fqgpmvbxfla>
Date: Thu, 27 Nov 2025 10:25:09 +0100
From: Thierry Reding <thierry.reding@...il.com>
To: "Sheetal ." <sheetal@...dia.com>
Cc: vkoul@...nel.org, ldewangan@...dia.com, jonathanh@...dia.com, 
	dmaengine@...r.kernel.org, linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dmaengine: tegra-adma: Fix use-after-free

On Mon, Nov 10, 2025 at 07:54:45PM +0530, Sheetal . wrote:
> From: Sheetal <sheetal@...dia.com>
> 
> A use-after-free bug exists in the Tegra ADMA driver when audio streams
> are terminated, particularly during XRUN conditions. The issue occurs
> when the DMA buffer is freed by tegra_adma_terminate_all() before the
> vchan completion tasklet finishes accessing it.
> 
> The race condition follows this sequence:
> 
>   1. DMA transfer completes, triggering an interrupt that schedules the
>      completion tasklet (tasklet has not executed yet)
>   2. Audio playback stops, calling tegra_adma_terminate_all() which
>      frees the DMA buffer memory via kfree()
>   3. The scheduled tasklet finally executes, calling vchan_complete()
>      which attempts to access the already-freed memory
> 
> Since tasklets can execute at any time after being scheduled, there is
> no guarantee that the buffer will remain valid when vchan_complete()
> runs.
> 
> Fix this by properly synchronizing the virtual channel completion:
>  - Calling vchan_terminate_vdesc() in tegra_adma_stop() to mark the
>    descriptors as terminated instead of freeing the descriptor.
>  - Add the callback tegra_adma_synchronize() that calls
>    vchan_synchronize() which kills any pending tasklets and frees any
>    terminated descriptors.
> 
> Crash logs:
> [  337.427523] BUG: KASAN: use-after-free in vchan_complete+0x124/0x3b0
> [  337.427544] Read of size 8 at addr ffff000132055428 by task swapper/0/0
> 
> [  337.427562] Call trace:
> [  337.427564]  dump_backtrace+0x0/0x320
> [  337.427571]  show_stack+0x20/0x30
> [  337.427575]  dump_stack_lvl+0x68/0x84
> [  337.427584]  print_address_description.constprop.0+0x74/0x2b8
> [  337.427590]  kasan_report+0x1f4/0x210
> [  337.427598]  __asan_load8+0xa0/0xd0
> [  337.427603]  vchan_complete+0x124/0x3b0
> [  337.427609]  tasklet_action_common.constprop.0+0x190/0x1d0
> [  337.427617]  tasklet_action+0x30/0x40
> [  337.427623]  __do_softirq+0x1a0/0x5c4
> [  337.427628]  irq_exit+0x110/0x140
> [  337.427633]  handle_domain_irq+0xa4/0xe0
> [  337.427640]  gic_handle_irq+0x64/0x160
> [  337.427644]  call_on_irq_stack+0x20/0x4c
> [  337.427649]  do_interrupt_handler+0x7c/0x90
> [  337.427654]  el1_interrupt+0x30/0x80
> [  337.427659]  el1h_64_irq_handler+0x18/0x30
> [  337.427663]  el1h_64_irq+0x7c/0x80
> [  337.427667]  cpuidle_enter_state+0xe4/0x540
> [  337.427674]  cpuidle_enter+0x54/0x80
> [  337.427679]  do_idle+0x2e0/0x380
> [  337.427685]  cpu_startup_entry+0x2c/0x70
> [  337.427690]  rest_init+0x114/0x130
> [  337.427695]  arch_call_rest_init+0x18/0x24
> [  337.427702]  start_kernel+0x380/0x3b4
> [  337.427706]  __primary_switched+0xc0/0xc8
> 
> Fixes: f46b195799b5 ("dmaengine: tegra-adma: Add support for Tegra210 ADMA")
> 
> Signed-off-by: Sheetal <sheetal@...dia.com>
> ---
>  drivers/dma/tegra210-adma.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)

Tiny nit-pick: there should be no blank line between the tags above
(i.e. between the Fixes: and Signed-off-by: lines).

Vinod, is that something you can fix up while applying, or do you want a
new patch for that?

In either case:

Acked-by: Thierry Reding <treding@...dia.com>

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