dma: contiguous: Check return value of dma_contiguous_reserve_area()

Commit 8f1fc1b ("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: 8f1fc1b ("dma: contiguous: Reserve default CMA heap")
Signed-off-by: Shanker Donthineni <[email protected]>
Reviewed-by: T.J. Mercier <[email protected]>
Signed-off-by: Marek Szyprowski <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

Author: shankerd04

kernel/dma/contiguous.c

@@ -257,10 +257,12 @@ 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)