* Re: [PATCH] dma: contiguous: Check return value of dma_contiguous_reserve_area()
2026-01-29 18:13 ` [PATCH] dma: contiguous: Check return value of dma_contiguous_reserve_area() Shanker Donthineni
@ 2026-01-29 18:43 ` T.J. Mercier
2026-02-02 15:52 ` Marek Szyprowski
1 sibling, 0 replies; 3+ messages in thread
From: T.J. Mercier @ 2026-01-29 18:43 UTC (permalink / raw)
To: Shanker Donthineni
Cc: Marek Szyprowski, Maxime Ripard, Robin Murphy, Sumit Semwal,
iommu, linux-kernel
On Thu, Jan 29, 2026 at 10:14 AM Shanker Donthineni
<sdonthineni@nvidia.com> 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@nvidia.com>
Might be good to add a pr_warn when dma_contiguous_reserve_area fails,
since we won't get the pr_warn for a dma_heap_cma_register_heap
failure when we return early.
Either way:
Reviewed-by: T.J. Mercier <tjmercier@google.com>
^ permalink raw reply [flat|nested] 3+ messages in thread* Re: [PATCH] dma: contiguous: Check return value of dma_contiguous_reserve_area()
2026-01-29 18:13 ` [PATCH] dma: contiguous: Check return value of dma_contiguous_reserve_area() Shanker Donthineni
2026-01-29 18:43 ` T.J. Mercier
@ 2026-02-02 15:52 ` Marek Szyprowski
1 sibling, 0 replies; 3+ messages in thread
From: Marek Szyprowski @ 2026-02-02 15:52 UTC (permalink / raw)
To: Shanker Donthineni, Maxime Ripard, Robin Murphy
Cc: Sumit Semwal, T . J . Mercier, iommu, linux-kernel
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@nvidia.com>
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
^ permalink raw reply [flat|nested] 3+ messages in thread