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NULL pointer dereference in obj_stock_flush_required() To: Dmitry Vyukov , Roman Gushchin Cc: Muchun Song , Linux Memory Management List , Andrew Morton , Johannes Weiner , Michal Hocko , Shakeel Butt , linux-kernel@vger.kernel.org, syzbot+774c29891415ab0fd29d@syzkaller.appspotmail.com Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 08E02120011 X-Stat-Signature: zgpujj5qa1gxisieipueeqdtqsnsoyka X-HE-Tag: 1682327585-216384 X-HE-Meta: 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 UdAdMG/t 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 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: On Sun, Apr 23, 2023 at 11:51=E2=80=AFPM Dmitry Vyukov = wrote: > > On Sun, 23 Apr 2023 at 04:26, Muchun Song wrote: > > > On Apr 22, 2023, at 01:40, Roman Gushchin = wrote: > > > > > > KCSAN found an issue in obj_stock_flush_required(): > > > stock->cached_objcg can be reset between the check and dereference: > > > > > > =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 > > > BUG: KCSAN: data-race in drain_all_stock / drain_obj_stock > > > > > > write to 0xffff888237c2a2f8 of 8 bytes by task 19625 on cpu 0: > > > drain_obj_stock+0x408/0x4e0 mm/memcontrol.c:3306 > > > refill_obj_stock+0x9c/0x1e0 mm/memcontrol.c:3340 > > > obj_cgroup_uncharge+0xe/0x10 mm/memcontrol.c:3408 > > > memcg_slab_free_hook mm/slab.h:587 [inline] > > > __cache_free mm/slab.c:3373 [inline] > > > __do_kmem_cache_free mm/slab.c:3577 [inline] > > > kmem_cache_free+0x105/0x280 mm/slab.c:3602 > > > __d_free fs/dcache.c:298 [inline] > > > dentry_free fs/dcache.c:375 [inline] > > > __dentry_kill+0x422/0x4a0 fs/dcache.c:621 > > > dentry_kill+0x8d/0x1e0 > > > dput+0x118/0x1f0 fs/dcache.c:913 > > > __fput+0x3bf/0x570 fs/file_table.c:329 > > > ____fput+0x15/0x20 fs/file_table.c:349 > > > task_work_run+0x123/0x160 kernel/task_work.c:179 > > > resume_user_mode_work include/linux/resume_user_mode.h:49 [inline] > > > exit_to_user_mode_loop+0xcf/0xe0 kernel/entry/common.c:171 > > > exit_to_user_mode_prepare+0x6a/0xa0 kernel/entry/common.c:203 > > > __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline] > > > syscall_exit_to_user_mode+0x26/0x140 kernel/entry/common.c:296 > > > do_syscall_64+0x4d/0xc0 arch/x86/entry/common.c:86 > > > entry_SYSCALL_64_after_hwframe+0x63/0xcd > > > > > > read to 0xffff888237c2a2f8 of 8 bytes by task 19632 on cpu 1: > > > obj_stock_flush_required mm/memcontrol.c:3319 [inline] > > > drain_all_stock+0x174/0x2a0 mm/memcontrol.c:2361 > > > try_charge_memcg+0x6d0/0xd10 mm/memcontrol.c:2703 > > > try_charge mm/memcontrol.c:2837 [inline] > > > mem_cgroup_charge_skmem+0x51/0x140 mm/memcontrol.c:7290 > > > sock_reserve_memory+0xb1/0x390 net/core/sock.c:1025 > > > sk_setsockopt+0x800/0x1e70 net/core/sock.c:1525 > > > udp_lib_setsockopt+0x99/0x6c0 net/ipv4/udp.c:2692 > > > udp_setsockopt+0x73/0xa0 net/ipv4/udp.c:2817 > > > sock_common_setsockopt+0x61/0x70 net/core/sock.c:3668 > > > __sys_setsockopt+0x1c3/0x230 net/socket.c:2271 > > > __do_sys_setsockopt net/socket.c:2282 [inline] > > > __se_sys_setsockopt net/socket.c:2279 [inline] > > > __x64_sys_setsockopt+0x66/0x80 net/socket.c:2279 > > > do_syscall_x64 arch/x86/entry/common.c:50 [inline] > > > do_syscall_64+0x41/0xc0 arch/x86/entry/common.c:80 > > > entry_SYSCALL_64_after_hwframe+0x63/0xcd > > > > > > value changed: 0xffff8881382d52c0 -> 0xffff888138893740 > > > > > > Reported by Kernel Concurrency Sanitizer on: > > > CPU: 1 PID: 19632 Comm: syz-executor.0 Not tainted 6.3.0-rc2-syzkalle= r-00387-g534293368afa #0 > > > Hardware name: Google Google Compute Engine/Google Compute Engine, BI= OS Google 03/02/2023 > > > > > > Fix it by reading the cached_objcg with READ_ONCE(). > > > > > > Fixes: bf4f059954dc ("mm: memcg/slab: obj_cgroup API") > > > Reported-by: syzbot+774c29891415ab0fd29d@syzkaller.appspotmail.com > > > Reported-by: Dmitry Vyukov > > > Link: https://lore.kernel.org/linux-mm/CACT4Y+ZfucZhM60YPphWiCLJr6+SG= FhT+jjm8k1P-a_8Kkxsjg@mail.gmail.com/T/#t > > > Signed-off-by: Roman Gushchin > > > > Acked-by: Muchun Song > > > > Thanks. > > This improves things, but strictly speaking the write side also needs > WRITE_ONCE. Ordering is always a game of two. It's not possible to > order things on one side, if the other side messes up the ordering. > It looks like most other accesses use memcg_stock.stock_lock for synchronization. Based on the output of obj_stock_flush_required() we call drain_local_stock(), which acquires that lock as well. Should we refactor the code to extend the lock section to cover both obj_stock_flush_required() and drain_local_stock()? IIUC this may unify the synchronization handling and READ_ONCE/WRITE_ONCE may no longer be needed. This should also avoid any inaccuracies (e.g. unnecessary flushes) that may happen if the cached objcg changes between obj_stock_flush_required() and drain_local_stock(). Did I miss anything here?