From: Uladzislau Rezki <uladzislau.rezki@xxxxxxxx> Subject: z3fold: fix use-after-free when freeing handles free_handle() for a foreign handle may race with inter-page compaction, what can lead to memory corruption. To avoid that, take write lock not read lock in free_handle to be synchronized with __release_z3fold_page(). For example KASAN can detect it: [ 33.723357] ================================================================== [ 33.723401] BUG: KASAN: use-after-free in LZ4_decompress_safe+0x2c4/0x3b8 [ 33.723418] Read of size 1 at addr ffffffc976695ca3 by task GoogleApiHandle/4121 [ 33.723428] [ 33.723449] CPU: 0 PID: 4121 Comm: GoogleApiHandle Tainted: P S OE 4.19.81-perf+ #162 [ 33.723461] Hardware name: Sony Mobile Communications. PDX-203(KONA) (DT) [ 33.723473] Call trace: [ 33.723495] dump_backtrace+0x0/0x288 [ 33.723512] show_stack+0x14/0x20 [ 33.723533] dump_stack+0xe4/0x124 [ 33.723551] print_address_description+0x80/0x2e0 [ 33.723566] kasan_report+0x268/0x2d0 [ 33.723584] __asan_load1+0x4c/0x58 [ 33.723601] LZ4_decompress_safe+0x2c4/0x3b8 [ 33.723619] lz4_decompress_crypto+0x3c/0x70 [ 33.723636] crypto_decompress+0x58/0x70 [ 33.723656] zcomp_decompress+0xd4/0x120 ... Apart from that, initialize zhdr->mapped_count in init_z3fold_page() and remove "newpage" variable because it is not used anywhere. Link: http://lkml.kernel.org/r/20200520082100.28876-1-vitaly.wool@xxxxxxxxxxxx Signed-off-by: Uladzislau Rezki <uladzislau.rezki@xxxxxxxx> Signed-off-by: Vitaly Wool <vitaly.wool@xxxxxxxxxxxx> Cc: Qian Cai <cai@xxxxxx> Cc: Raymond Jennings <shentino@xxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/z3fold.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) --- a/mm/z3fold.c~z3fold-fix-use-after-free-when-freeing-handles +++ a/mm/z3fold.c @@ -318,16 +318,16 @@ static inline void free_handle(unsigned slots = handle_to_slots(handle); write_lock(&slots->lock); *(unsigned long *)handle = 0; - write_unlock(&slots->lock); - if (zhdr->slots == slots) + if (zhdr->slots == slots) { + write_unlock(&slots->lock); return; /* simple case, nothing else to do */ + } /* we are freeing a foreign handle if we are here */ zhdr->foreign_handles--; is_free = true; - read_lock(&slots->lock); if (!test_bit(HANDLES_ORPHANED, &slots->pool)) { - read_unlock(&slots->lock); + write_unlock(&slots->lock); return; } for (i = 0; i <= BUDDY_MASK; i++) { @@ -336,7 +336,7 @@ static inline void free_handle(unsigned break; } } - read_unlock(&slots->lock); + write_unlock(&slots->lock); if (is_free) { struct z3fold_pool *pool = slots_to_pool(slots); @@ -422,6 +422,7 @@ static struct z3fold_header *init_z3fold zhdr->start_middle = 0; zhdr->cpu = -1; zhdr->foreign_handles = 0; + zhdr->mapped_count = 0; zhdr->slots = slots; zhdr->pool = pool; INIT_LIST_HEAD(&zhdr->buddy); _
