On Mon, Apr 15, 2024 at 7:26 PM Dan Clash <daclash@xxxxxxxxxxxxxxxxxxx> wrote: > > Below is a test program that causes multiple io_uring worker threads to > hit a NULL dereference while executing openat ops. > > The test program hangs forever in a D state. The test program can be > run again after the NULL dereferences. However, there are long delays > at reboot time because the io_uring_cancel() during do_exit() attempts > to wake the worker threads. > > The test program is single threaded but it queues multiple openat and > close ops with IOSQE_ASYNC set before waiting for completions. > > I collected trace with /sys/kernel/tracing/events/io_uring/enable > enabled if that is helpful. > > The test program reproduces similar problems in the following releases. > > mainline v6.9-rc3 > stable 6.8.5 > Ubuntu 6.5.0-1018-azure > > The test program does not reproduce the problem in Ubuntu > 5.15.0-1052-azure, which does not have the io_uring audit changes. > > The following is the first io_uring worker thread backtrace in the repro > against v6.9-rc3. > > BUG: kernel NULL pointer dereference, address: 0000000000000000 > #PF: supervisor read access in kernel mode > #PF: error_code(0x0000) - not-present page > PGD 0 P4D 0 > Oops: 0000 [#1] SMP PTI > CPU: 0 PID: 4628 Comm: iou-wrk-4605 Not tainted 6.9.0-rc3 #2 > Hardware name: Microsoft Corporation Virtual Machine/Virtual Machine, > BIOS Hyper-V UEFI Release v4.1 11/28/2023 > RIP: 0010:strlen (lib/string.c:402) > Call Trace: > <TASK> > ? show_regs (arch/x86/kernel/dumpstack.c:479) > ? __die (arch/x86/kernel/dumpstack.c:421 arch/x86/kernel/dumpstack.c:434) > ? page_fault_oops (arch/x86/mm/fault.c:713) > ? do_user_addr_fault (arch/x86/mm/fault.c:1261) > ? exc_page_fault (./arch/x86/include/asm/irqflags.h:37 > ./arch/x86/include/asm/irqflags.h:72 arch/x86/mm/fault.c:1513 > arch/x86/mm/fault.c:1563) > ? asm_exc_page_fault (./arch/x86/include/asm/idtentry.h:623) > ? __pfx_strlen (lib/string.c:402) > ? parent_len (kernel/auditfilter.c:1284). > __audit_inode (kernel/auditsc.c:2381 (discriminator 4)) Thanks for the well documented bug report! That's interesting, it looks like audit_inode() is potentially being passed a filename struct with a NULL name field (filename::name == NULL). Given the IOSQE_ASYNC and what looks like io_uring calling getname() from within the __io_openat_prep() function, I suspect the issue is that we aren't associating the filename information we collect in getname() with the proper audit_context(). In other words, we do the getname() in one context, and then the actual open operation in another, and the audit filename info is lost in the switch. I think this is related to another issue that Jens and I have been discussing relating to connect() and sockaddrs. We had been hoping that the issue we were seeing with sockaddrs was just a special case with connect, but it doesn't look like that is the case. I'm going to be a bit busy this week with conferences, but given the previous discussions with Jens as well as this new issue, I suspect that we are going to need to do some work to support creation of a thin, or lazily setup, audit_context that we can initialize in the io_uring prep routines for use by getname(), move_addr_to_kernel(), etc., store in the io_kiocb struct, and then fully setup in audit_uring_entry(). > ? link_path_walk.part.0.constprop.0 (fs/namei.c:2324) > path_openat (fs/namei.c:3550 fs/namei.c:3796) > do_filp_open (fs/namei.c:3826) > ? alloc_fd (./arch/x86/include/asm/paravirt.h:589 (discriminator 10) > ./arch/x86/include/asm/qspinlock.h:57 (discriminator 10) > ./include/linux/spinlock.h:204 (discriminator 10) > ./include/linux/spinlock_api_smp.h:142 (discriminator 10) > ./include/linux/spinlock.h:391 (discriminator 10) fs/file.c:553 > (discriminator 10)) > io_openat2 (io_uring/openclose.c:140) > io_openat (io_uring/openclose.c:178) > io_issue_sqe (io_uring/io_uring.c:1897) > io_wq_submit_work (io_uring/io_uring.c:2006) > io_worker_handle_work (io_uring/io-wq.c:540 io_uring/io-wq.c:597) > io_wq_worker (io_uring/io-wq.c:258 io_uring/io-wq.c:648) > ? __pfx_io_wq_worker (io_uring/io-wq.c:627) > ? raw_spin_rq_unlock (./arch/x86/include/asm/paravirt.h:589 > ./arch/x86/include/asm/qspinlock.h:57 ./include/linux/spinlock.h:204 > ./include/linux/spinlock_api_smp.h:142 kernel/sched/core.c:603) > ? finish_task_switch.isra.0 (./arch/x86/include/asm/irqflags.h:42 > ./arch/x86/include/asm/irqflags.h:77 kernel/sched/sched.h:1397 > kernel/sched/core.c:5163 kernel/sched/core.c:5281) > ? __pfx_io_wq_worker (io_uring/io-wq.c:627) > ret_from_fork (arch/x86/kernel/process.c:156) > ? __pfx_io_wq_worker (io_uring/io-wq.c:627) > ret_from_fork_asm (arch/x86/entry/entry_64.S:256) -- paul-moore.com
