PENDING: nvme-pci: fix race condition in dma_need_unmap #221
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The nvme_pci_prp_iter_next function had a race condition where dma_need_unmap() could return true indicating DMA unmapping is needed, but iod->dma_vecs was NULL, causing a NULL pointer dereference. This occurred because: 1. dma_vecs allocation happens in nvme_pci_setup_data_prp() 2. nvme_pci_prp_iter_next() checks dma_need_unmap() but doesn't verify if dma_vecs allocation was successful 3. If allocation failed or race condition occurred, accessing dma_vecs[0] would cause kernel crash The crash manifested as: - dma_size:0 unmap:0 initially, then dma_size:0 unmap:1 - nr_dma_vecs:0 dma_vecs:0x0 (NULL pointer) - Unable to handle kernel NULL pointer dereference at virtual address 0x0. Fix by adding iod->dma_vecs NULL check to the condition in nvme_pci_prp_iter_next(), ensuring DMA vector operations only occur when the dma_vecs array has been successfully allocated. Signed-off-by: Nitin Rawat <[email protected]>
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The nvme_pci_prp_iter_next function had a race condition where dma_need_unmap() could return true indicating DMA unmapping is needed, but iod->dma_vecs was NULL, causing a NULL pointer dereference.
This occurred because:
The crash manifested as:
Fix by adding iod->dma_vecs NULL check to the condition in nvme_pci_prp_iter_next(), ensuring DMA vector operations only occur when the dma_vecs array has been successfully allocated.