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mm: vmalloc: ensure vmap_block is initialised before adding to queue
Commit 8c61291 ("mm: fix incorrect vbq reference in purge_fragmented_block") extended the 'vmap_block' structure to contain a 'cpu' field which is set at allocation time to the id of the initialising CPU. When a new 'vmap_block' is being instantiated by new_vmap_block(), the partially initialised structure is added to the local 'vmap_block_queue' xarray before the 'cpu' field has been initialised. If another CPU is concurrently walking the xarray (e.g. via vm_unmap_aliases()), then it may perform an out-of-bounds access to the remote queue thanks to an uninitialised index. This has been observed as UBSAN errors in Android: | Internal error: UBSAN: array index out of bounds: 00000000f2005512 [#1] PREEMPT SMP | | Call trace: | purge_fragmented_block+0x204/0x21c | _vm_unmap_aliases+0x170/0x378 | vm_unmap_aliases+0x1c/0x28 | change_memory_common+0x1dc/0x26c | set_memory_ro+0x18/0x24 | module_enable_ro+0x98/0x238 | do_init_module+0x1b0/0x310 Move the initialisation of 'vb->cpu' in new_vmap_block() ahead of the addition to the xarray. Link: https://lkml.kernel.org/r/[email protected] Fixes: 8c61291 ("mm: fix incorrect vbq reference in purge_fragmented_block") Signed-off-by: Will Deacon <[email protected]> Reviewed-by: Baoquan He <[email protected]> Reviewed-by: Uladzislau Rezki (Sony) <[email protected]> Cc: Zhaoyang Huang <[email protected]> Cc: Hailong.Liu <[email protected]> Cc: Christoph Hellwig <[email protected]> Cc: Lorenzo Stoakes <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: <[email protected]> Signed-off-by: Andrew Morton <[email protected]>
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