Re: [PATCH] z3fold: fix use-after-free when freeing handles

[Vitaly Wool <vitaly.wool@konsulko.com>]

On Thu, May 21, 2020 at 2:46 AM Andrew Morton <akpm@linux-foundation.org> wrote:
>
> On Wed, 20 May 2020 11:21:00 +0300 vitaly.wool@konsulko.com wrote:
>
> > From: Uladzislau Rezki <uladzislau.rezki@sony.com>
> >
> > 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.
> >
> > Signed-off-by: Uladzislau Rezki <uladzislau.rezki@sony.com>
> > Signed-off-by: Vitaly Wool <vitaly.wool@konsulko.com>
>
> I assume that a cc:stable is appropriate here?

Absolutely. stable was in fact in CC: but it didn't reflect in the
patch for some reason. Thanks!

~Vitaly