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Tue, 14 Feb 2023 18:37:56 +0000 From: Munehisa Kamata To: CC: , , , , , , Subject: Re: [PATCH v2] sched/psi: fix use-after-free in ep_remove_wait_queue() Date: Tue, 14 Feb 2023 10:37:45 -0800 Message-ID: <20230214183745.3958175-1-kamatam@amazon.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain X-Originating-IP: [10.43.161.198] X-ClientProxiedBy: EX13D36UWA002.ant.amazon.com (10.43.160.24) To EX19D010UWA004.ant.amazon.com (10.13.138.204) X-Rspam-User: X-Rspamd-Server: rspam03 X-Stat-Signature: 3pbcje54niae3r9dy67cun6cf65fcqxj X-Rspamd-Queue-Id: 31D524000A X-HE-Tag: 1676399880-96456 X-HE-Meta: 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 zXcIvQ4B 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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 Tue, 2023-02-14 17:10:58 +0000, Suren Baghdasaryan wrote: > > 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. Applied in v3. > > > > 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: Applied in v3. > > > > 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. Applied in v3. > > > > 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. Applied in v3 as well. > > 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" ? Removed it in v3. The subject of the original sentense was a bit unclear to me and I think I tried to have a simplified version of "[Otherwise an unexpected free of the queue] can happen if ... " there. Thanks for all the suggestions. Regards, Munehisa > > */ > > - wake_up_interruptible(&t->event_wait); > > + wake_up_pollfree(&t->event_wait); > > > > mutex_lock(&group->trigger_lock); > > > > -- > > 2.38.1 > > >