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Tue, 14 Feb 2023 09:11:09 -0800 (PST) MIME-Version: 1.0 References: <20230214070429.3613260-1-kamatam@amazon.com> In-Reply-To: <20230214070429.3613260-1-kamatam@amazon.com> From: Suren Baghdasaryan Date: Tue, 14 Feb 2023 09:10:58 -0800 Message-ID: Subject: Re: [PATCH v2] sched/psi: fix use-after-free in ep_remove_wait_queue() To: Munehisa Kamata Cc: ebiggers@kernel.org, hannes@cmpxchg.org, hdanton@sina.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, mengcc@amazon.com, stable@vger.kernel.org Content-Type: text/plain; charset="UTF-8" X-Rspam-User: X-Rspamd-Queue-Id: F384A4000B X-Rspamd-Server: rspam01 X-Stat-Signature: cmicysoq74quxj6nu9rnfsqjrt8ig4w6 X-HE-Tag: 1676394670-602174 X-HE-Meta: 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 +jXMsTUY yjUUzpjhk1ut39mCr0AqpIFRuZHwLBcPT005GkuZHDWJZIaQFczZSiZn6wn5uPzDMCUnKgccxdzFEBYDpOZBDQ/4uAaPietF0jkNWGUtapvBNQkzYR+JsLk9OnoHz2SAEQDx9u/LR9RoQ3mjIcpL8S8FlkDsU4ID+7abYKv7wdAy9tXWJOXZ/06MC4Yk3JniaJfb5cK8OTiUfvJKK/vJpBvN02O8TdiAIu+Go9l5fR10X2TzUz6XLYh9ioycmPl4mKh6nb68xGeDznVNaWb/mmKGDItCVEKYp9JRamBg2kT+2COdfQnkqKbTngT2GgcMwU42L3FxJSQVO/GP8w5UbevjIELbSXUJl9Qp3ob2KE8ft0YoDI04xqo/K0w== 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: Thanks! Overall LGTM, just a couple of nits (simplifications): On Mon, Feb 13, 2023 at 11:04 PM Munehisa Kamata wrote: > > If a non-root cgroup gets removed when there is a thread that registered > trigger and is polling on a pressure file within the cgroup, the polling > waitqueue gets freed without clearing the queue and reference in the > following path. Let's remove "without clearing the queue and reference" in the above sentence. The next section explains why this is problematic, therefore mentioning that here is unnecessary IMHO. > > do_rmdir > cgroup_rmdir > kernfs_drain_open_files > cgroup_file_release > cgroup_pressure_release > psi_trigger_destroy > > However, the polling thread can keep having the last reference to the > pressure file that is tied to the freed waitqueue until explicit close or > exit later. Suggest replacing: However, the polling thread still has a reference to the pressure file it is polling and will access the freed waitqueue when file is closed or upon exit: > > fput > ep_eventpoll_release > ep_free > ep_remove_wait_queue > remove_wait_queue > > Then, the thread accesses to the already-freed waitqueue when dropping the > reference and results in use-after-free as pasted below. Suggest replacing: This results is use-after-free as pasted below. > > The fundamental problem here is that the lifetime of the waitqueue is not > tied to the file's real lifetime as shown above. The fundamental problem here is that cgroup_file_release() (and consequently waitqueue's lifetime) is not tied to the file's real lifetime. > Using wake_up_pollfree() > here might be less than ideal, but it also is not fully contradicting the > comment at commit 42288cb44c4b ("wait: add wake_up_pollfree()") since the > waitqueue's lifetime is not tied to file's one and can be considered as > another special case. While this would be fixable by somehow making > cgroup_file_release() be tied to the fput(), it would require sizable > refactoring at cgroups or higher layer which might be more justifiable if > we identify more cases like this. > > BUG: KASAN: use-after-free in _raw_spin_lock_irqsave+0x60/0xc0 > Write of size 4 at addr ffff88810e625328 by task a.out/4404 > > CPU: 19 PID: 4404 Comm: a.out Not tainted 6.2.0-rc6 #38 > Hardware name: Amazon EC2 c5a.8xlarge/, BIOS 1.0 10/16/2017 > Call Trace: > > dump_stack_lvl+0x73/0xa0 > print_report+0x16c/0x4e0 > ? _printk+0x59/0x80 > ? __virt_addr_valid+0xb8/0x130 > ? _raw_spin_lock_irqsave+0x60/0xc0 > kasan_report+0xc3/0xf0 > ? _raw_spin_lock_irqsave+0x60/0xc0 > kasan_check_range+0x2d2/0x310 > _raw_spin_lock_irqsave+0x60/0xc0 > remove_wait_queue+0x1a/0xa0 > ep_free+0x12c/0x170 > ep_eventpoll_release+0x26/0x30 > __fput+0x202/0x400 > task_work_run+0x11d/0x170 > do_exit+0x495/0x1130 > ? update_cfs_rq_load_avg+0x2c2/0x2e0 > do_group_exit+0x100/0x100 > get_signal+0xd67/0xde0 > ? finish_task_switch+0x15f/0x3a0 > arch_do_signal_or_restart+0x2a/0x2b0 > exit_to_user_mode_prepare+0x94/0x100 > syscall_exit_to_user_mode+0x20/0x40 > do_syscall_64+0x52/0x90 > entry_SYSCALL_64_after_hwframe+0x63/0xcd > RIP: 0033:0x7f8e392bfb91 > Code: Unable to access opcode bytes at 0x7f8e392bfb67. > RSP: 002b:00007fff261e08d8 EFLAGS: 00000246 ORIG_RAX: 0000000000000022 > RAX: fffffffffffffdfe RBX: 0000000000000000 RCX: 00007f8e392bfb91 > RDX: 0000000000000001 RSI: 00007fff261e08e8 RDI: 0000000000000004 > RBP: 00007fff261e0920 R08: 0000000000400780 R09: 00007f8e3960f240 > R10: 00000000000003df R11: 0000000000000246 R12: 00000000004005a0 > R13: 00007fff261e0a00 R14: 0000000000000000 R15: 0000000000000000 > > > Allocated by task 4404: > kasan_set_track+0x3d/0x60 > __kasan_kmalloc+0x85/0x90 > psi_trigger_create+0x113/0x3e0 > pressure_write+0x146/0x2e0 > cgroup_file_write+0x11c/0x250 > kernfs_fop_write_iter+0x186/0x220 > vfs_write+0x3d8/0x5c0 > ksys_write+0x90/0x110 > do_syscall_64+0x43/0x90 > entry_SYSCALL_64_after_hwframe+0x63/0xcd > > Freed by task 4407: > kasan_set_track+0x3d/0x60 > kasan_save_free_info+0x27/0x40 > ____kasan_slab_free+0x11d/0x170 > slab_free_freelist_hook+0x87/0x150 > __kmem_cache_free+0xcb/0x180 > psi_trigger_destroy+0x2e8/0x310 > cgroup_file_release+0x4f/0xb0 > kernfs_drain_open_files+0x165/0x1f0 > kernfs_drain+0x162/0x1a0 > __kernfs_remove+0x1fb/0x310 > kernfs_remove_by_name_ns+0x95/0xe0 > cgroup_addrm_files+0x67f/0x700 > cgroup_destroy_locked+0x283/0x3c0 > cgroup_rmdir+0x29/0x100 > kernfs_iop_rmdir+0xd1/0x140 > vfs_rmdir+0xfe/0x240 > do_rmdir+0x13d/0x280 > __x64_sys_rmdir+0x2c/0x30 > do_syscall_64+0x43/0x90 > entry_SYSCALL_64_after_hwframe+0x63/0xcd > > v2: updated commit message > > Link: https://lore.kernel.org/lkml/20230106224859.4123476-1-kamatam@amazon.com/ > Fixes: 0e94682b73bf ("psi: introduce psi monitor") > Cc: stable@vger.kernel.org > Signed-off-by: Munehisa Kamata > Signed-off-by: Mengchi Cheng > --- > kernel/sched/psi.c | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c > index 8ac8b81bfee6..6e66c15f6450 100644 > --- a/kernel/sched/psi.c > +++ b/kernel/sched/psi.c > @@ -1343,10 +1343,11 @@ void psi_trigger_destroy(struct psi_trigger *t) > > group = t->group; > /* > - * Wakeup waiters to stop polling. Can happen if cgroup is deleted > - * from under a polling process. > + * Wakeup waiters to stop polling and clear the queue to prevent it from > + * being accessed later. Can happen if cgroup is deleted from under a > + * polling process otherwise. This "otherwise" at the end seems extra. Was there a continuation of this comment which was removed without removing this "otherwise" ? > */ > - wake_up_interruptible(&t->event_wait); > + wake_up_pollfree(&t->event_wait); > > mutex_lock(&group->trigger_lock); > > -- > 2.38.1 >