Re: [PATCH] dma: contiguous: Check return value of dma_contiguous_reserve_area()

[Marek Szyprowski]

On 29.01.2026 19:13, Shanker Donthineni wrote:
> Commit 8f1fc1bf1a3d ("dma: contiguous: Reserve default CMA heap")
> introduced a bug where dma_heap_cma_register_heap() is called with
> a NULL pointer when dma_contiguous_reserve_area() fails to reserve
> the CMA area.
>
> When dma_contiguous_reserve_area() fails, dma_contiguous_default_area
> remains NULL (initialized as a global variable), but the code doesn't
> check the return value and proceeds to call dma_heap_cma_register_heap()
> with this NULL pointer.
>
> Later during boot, add_cma_heaps() iterates through the dma_areas[]
> array and attempts to register heaps. When it encounters the NULL
> pointer stored by the earlier call, it crashes in __add_cma_heap()
> -> dma_heap_add() when trying to dereference the NULL CMA pointer.
>
> The crash manifests as:
>    Unable to handle kernel NULL pointer dereference at virtual address
>    0000000000000038
>    ...
>    Call trace:
>     dma_heap_add+0x40/0x2b0
>     __add_cma_heap+0x80/0xe0
>     add_cma_heaps+0x64/0xb0
>     do_one_initcall+0x60/0x318
>     kernel_init_freeable+0x260/0x2f0
>     kernel_init+0x2c/0x168
>     ret_from_fork+0x10/0x20
>
> Fix this by checking the return value of dma_contiguous_reserve_area()
> and only calling dma_heap_cma_register_heap() when the reservation
> succeeds.
>
> Fixes: 8f1fc1bf1a3d ("dma: contiguous: Reserve default CMA heap")
> Signed-off-by: Shanker Donthineni <sdonthineni@xxxxxxxxxx>
Applied to dma-mapping-fixes, thanks!
> ---
>   kernel/dma/contiguous.c | 10 ++++++----
>   1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
> index d8fd6f779f797..92c539d76412b 100644
> --- a/kernel/dma/contiguous.c
> +++ b/kernel/dma/contiguous.c
> @@ -247,10 +247,12 @@ void __init dma_contiguous_reserve(phys_addr_t limit)
>   		pr_debug("%s: reserving %ld MiB for global area\n", __func__,
>   			 (unsigned long)selected_size / SZ_1M);
>   
> -		dma_contiguous_reserve_area(selected_size, selected_base,
> -					    selected_limit,
> -					    &dma_contiguous_default_area,
> -					    fixed);
> +		ret = dma_contiguous_reserve_area(selected_size, selected_base,
> +						  selected_limit,
> +						  &dma_contiguous_default_area,
> +						  fixed);
> +		if (ret)
> +			return;
>   
>   		ret = dma_heap_cma_register_heap(dma_contiguous_default_area);
>   		if (ret)

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland