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Commit 8cc3bad9d9d6 ("spi: Remove unneded check for orig_nents") introduced a regression: unmapped data could now be passed to the DMA APIs, resulting in null pointer dereferences. Commit 9f788ba457b4 ("spi: Don't mark message DMA mapped when no transfer in it is") and commit da560097c056 ("spi: Check if transfer is mapped before calling DMA sync APIs") addressed the problem, but only partially. Unidirectional transactions will still result in null pointer dereference. To prevent that from happening, assign a dummy scatterlist when no data is mapped, so that the DMA API can be called and not result in a null pointer dereference. Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Reported-by: Neil Armstrong <neil.armstrong@linaro.org> Closes: https://lore.kernel.org/r/8ae675b5-fcf9-4c9b-b06a-4462f70e1322@linaro.org Reported-by: Nícolas F. R. A. Prado <nfraprado@collabora.com> Closes: https://lore.kernel.org/all/d3679496-2e4e-4a7c-97ed-f193bd53af1d@notapiano Closes: https://lore.kernel.org/all/4748499f-789c-45a8-b50a-2dd09f4bac8c@notapiano Fixes: 8cc3bad9d9d6 ("spi: Remove unneded check for orig_nents") Tested-by: Nícolas F. R. A. Prado <nfraprado@collabora.com> [nfraprado: wrote the commit message] Signed-off-by: Nícolas F. R. A. Prado <nfraprado@collabora.com> Link: https://msgid.link/r/20240529-dma-oops-dummy-v1-1-bb43aacfb11b@collabora.com Signed-off-by: Mark Brown <broonie@kernel.org>