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[92.247.61.126]) by smtp.gmail.com with ESMTPSA id 89sm2071486wrj.37.2020.05.20.01.21.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 20 May 2020 01:21:05 -0700 (PDT) From: vitaly.wool@konsulko.com To: linux-mm@kvack.org Cc: stable@kernel.org, cai@lca.pw, shentino@gmail.com, akpm@linux-foundation.org, Uladzislau Rezki , Vitaly Wool Subject: [PATCH] z3fold: fix use-after-free when freeing handles Date: Wed, 20 May 2020 11:21:00 +0300 Message-Id: <20200520082100.28876-1-vitaly.wool@konsulko.com> X-Mailer: git-send-email 2.20.1 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: From: Uladzislau Rezki 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] =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D [ 33.723401] BUG: KASAN: use-after-free in LZ4_decompress_safe+0x2c4/0x= 3b8 [ 33.723418] Read of size 1 at addr ffffffc976695ca3 by task GoogleApiH= andle/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 Signed-off-by: Vitaly Wool --- mm/z3fold.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/mm/z3fold.c b/mm/z3fold.c index 42f31c4b53ad..8c3bb5e508b8 100644 --- a/mm/z3fold.c +++ b/mm/z3fold.c @@ -318,16 +318,16 @@ static inline void free_handle(unsigned long handle= ) slots =3D handle_to_slots(handle); write_lock(&slots->lock); *(unsigned long *)handle =3D 0; - write_unlock(&slots->lock); - if (zhdr->slots =3D=3D slots) + if (zhdr->slots =3D=3D slots) { + write_unlock(&slots->lock); return; /* simple case, nothing else to do */ + } =20 /* we are freeing a foreign handle if we are here */ zhdr->foreign_handles--; is_free =3D true; - read_lock(&slots->lock); if (!test_bit(HANDLES_ORPHANED, &slots->pool)) { - read_unlock(&slots->lock); + write_unlock(&slots->lock); return; } for (i =3D 0; i <=3D BUDDY_MASK; i++) { @@ -336,7 +336,7 @@ static inline void free_handle(unsigned long handle) break; } } - read_unlock(&slots->lock); + write_unlock(&slots->lock); =20 if (is_free) { struct z3fold_pool *pool =3D slots_to_pool(slots); @@ -422,6 +422,7 @@ static struct z3fold_header *init_z3fold_page(struct = page *page, bool headless, zhdr->start_middle =3D 0; zhdr->cpu =3D -1; zhdr->foreign_handles =3D 0; + zhdr->mapped_count =3D 0; zhdr->slots =3D slots; zhdr->pool =3D pool; INIT_LIST_HEAD(&zhdr->buddy); --=20 2.20.1