In the Linux kernel, the following vulnerability has been resolved: crypto: sun8i-ce - Fix use after free in unprepare sun8i_ce_cipher_unprepare should be called before crypto_finalize_skcipher_request, because client callbacks may immediately free memory, that isn't needed anymore. But it will be used by unprepare after free. Before removing prepare/unprepare callbacks it was handled by crypto engine in crypto_finalize_request. Usually that results in a pointer dereference problem during a in crypto selftest. Unable to handle kernel NULL pointer dereference at virtual address 0000000000000030 Mem abort info: ESR = 0x0000000096000004 EC = 0x25: DABT (current EL), IL = 32 bits SET = 0, FnV = 0 EA = 0, S1PTW = 0 FSC = 0x04: level 0 translation fault Data abort info: ISV = 0, ISS = 0x00000004, ISS2 = 0x00000000 CM = 0, WnR = 0, TnD = 0, TagAccess = 0 GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0 user pgtable: 4k pages, 48-bit VAs, pgdp=000000004716d000 [0000000000000030] pgd=0000000000000000, p4d=0000000000000000 Internal error: Oops: 0000000096000004 [#1] SMP This problem is detected by KASAN as well. ================================================================== BUG: KASAN: slab-use-after-free in sun8i_ce_cipher_do_one+0x6e8/0xf80 [sun8i_ce] Read of size 8 at addr ffff00000dcdc040 by task 1c15000.crypto-/373 Hardware name: Pine64 PinePhone (1.2) (DT) Call trace: dump_backtrace+0x9c/0x128 show_stack+0x20/0x38 dump_stack_lvl+0x48/0x60 print_report+0xf8/0x5d8 kasan_report+0x90/0xd0 __asan_load8+0x9c/0xc0 sun8i_ce_cipher_do_one+0x6e8/0xf80 [sun8i_ce] crypto_pump_work+0x354/0x620 [crypto_engine] kthread_worker_fn+0x244/0x498 kthread+0x168/0x178 ret_from_fork+0x10/0x20 Allocated by task 379: kasan_save_stack+0x3c/0x68 kasan_set_track+0x2c/0x40 kasan_save_alloc_info+0x24/0x38 __kasan_kmalloc+0xd4/0xd8 __kmalloc+0x74/0x1d0 alg_test_skcipher+0x90/0x1f0 alg_test+0x24c/0x830 cryptomgr_test+0x38/0x60 kthread+0x168/0x178 ret_from_fork+0x10/0x20 Freed by task 379: kasan_save_stack+0x3c/0x68 kasan_set_track+0x2c/0x40 kasan_save_free_info+0x38/0x60 __kasan_slab_free+0x100/0x170 slab_free_freelist_hook+0xd4/0x1e8 __kmem_cache_free+0x15c/0x290 kfree+0x74/0x100 kfree_sensitive+0x80/0xb0 alg_test_skcipher+0x12c/0x1f0 alg_test+0x24c/0x830 cryptomgr_test+0x38/0x60 kthread+0x168/0x178 ret_from_fork+0x10/0x20 The buggy address belongs to the object at ffff00000dcdc000 which belongs to the cache kmalloc-256 of size 256 The buggy address is located 64 bytes inside of freed 256-byte region [ffff00000dcdc000, ffff00000dcdc100)
The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory "belongs" to the code that operates on the new pointer.