Messages in this thread | | | Date | Tue, 19 Jul 2022 18:36:10 +0100 | From | Will Deacon <> | Subject | Re: [POSSIBLE BUG] iommu/io-pgtable-arm: possible dereferencing of NULL pointer |
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On Mon, Jul 18, 2022 at 12:20:06PM +0300, Subkhankulov Rustam wrote: > Version: 5-19-rc6 > > In function '__arm_lpae_alloc_pages' pointer 'dev' is compared with > NULL at [drivers/iommu/io-pgtable-arm.c: 203]. This means that the > pointer can be NULL. > > ----------------------------------------------------------------------- > 203 p = alloc_pages_node(dev ? dev_to_node(dev) : NUMA_NO_NODE, > 204 gfp | __GFP_ZERO, order); > ----------------------------------------------------------------------- > > Then, if cfg->coherent_walk == 0 at [drivers/iommu/io-pgtable-arm.c: > 209], function 'dma_map_single', which is defined as > 'dma_map_single_attrs', is called and pointer dev is passed as > first parameter. > > ----------------------------------------------------------------------- > 209 if (!cfg->coherent_walk) { > 208 dma = dma_map_single(dev, pages, size, DMA_TO_DEVICE); > ----------------------------------------------------------------------- > > Therefore, pointer 'dev' passed to function 'dev_driver_string' > in macro 'dev_WARN_ONCE' at [include/linux/dma-mapping.h: 326], > where it is dereferenced at [drivers/base/core.c: 2091]. > > ----------------------------------------------------------------------- > 2083 const char *dev_driver_string(const struct device *dev) > 2084 { > 2085 struct device_driver *drv; > 2086 > --- > 2091 drv = READ_ONCE(dev->driver); > ----------------------------------------------------------------------- > > Thus, if it is possible that 'dev' is null at the same time > that flag 'coherent_walk' is 0, then NULL pointer will be > dereferenced. > > Should we somehow avoid NULL pointer dereference or is this > situation impossible and we should remove comparison with NULL?
I think 'dev' is only null in the case of the selftest initcall (see arm_lpae_do_selftests()), and 'coherent_walk' is always true there.
Will
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