On 11/2/20 4:54 AM, syzbot wrote: > Hello, > > syzbot found the following issue on: > > HEAD commit: 4e78c578 Add linux-next specific files for 20201030 > git tree: linux-next > console output: https://syzkaller.appspot.com/x/log.txt?x=148969d4500000 > kernel config: https://syzkaller.appspot.com/x/.config?x=83318758268dc331 > dashboard link: https://syzkaller.appspot.com/bug?extid=b57abf7ee60829090495 > compiler: gcc (GCC) 10.1.0-syz 20200507 > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17e1346c500000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1388fbca500000 > > The issue was bisected to: > > commit 4d004099a668c41522242aa146a38cc4eb59cb1e > Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > Date: Fri Oct 2 09:04:21 2020 +0000 > > lockdep: Fix lockdep recursion > > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=1354e614500000 > final oops: https://syzkaller.appspot.com/x/report.txt?x=10d4e614500000 > console output: https://syzkaller.appspot.com/x/log.txt?x=1754e614500000 > > IMPORTANT: if you fix the issue, please add the following tag to the commit: > Reported-by: syzbot+b57abf7ee60829090495@xxxxxxxxxxxxxxxxxxxxxxxxx > Fixes: 4d004099a668 ("lockdep: Fix lockdep recursion") > > ================================================================== > BUG: KASAN: null-ptr-deref in instrument_atomic_read_write include/linux/instrumented.h:101 [inline] > BUG: KASAN: null-ptr-deref in atomic_inc include/asm-generic/atomic-instrumented.h:240 [inline] > BUG: KASAN: null-ptr-deref in mmgrab include/linux/sched/mm.h:36 [inline] > BUG: KASAN: null-ptr-deref in kthread_use_mm+0x11c/0x2a0 kernel/kthread.c:1257 > Write of size 4 at addr 0000000000000060 by task io_uring-sq/26191 > > CPU: 1 PID: 26191 Comm: io_uring-sq Not tainted 5.10.0-rc1-next-20201030-syzkaller #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > Call Trace: > __dump_stack lib/dump_stack.c:77 [inline] > dump_stack+0x107/0x163 lib/dump_stack.c:118 > __kasan_report mm/kasan/report.c:549 [inline] > kasan_report.cold+0x5/0x37 mm/kasan/report.c:562 > check_memory_region_inline mm/kasan/generic.c:186 [inline] > check_memory_region+0x13d/0x180 mm/kasan/generic.c:192 > instrument_atomic_read_write include/linux/instrumented.h:101 [inline] > atomic_inc include/asm-generic/atomic-instrumented.h:240 [inline] > mmgrab include/linux/sched/mm.h:36 [inline] > kthread_use_mm+0x11c/0x2a0 kernel/kthread.c:1257 > __io_sq_thread_acquire_mm fs/io_uring.c:1092 [inline] > __io_sq_thread_acquire_mm+0x1c4/0x220 fs/io_uring.c:1085 > io_sq_thread_acquire_mm_files.isra.0+0x125/0x180 fs/io_uring.c:1104 > io_init_req fs/io_uring.c:6661 [inline] > io_submit_sqes+0x89d/0x25f0 fs/io_uring.c:6757 > __io_sq_thread fs/io_uring.c:6904 [inline] > io_sq_thread+0x462/0x1630 fs/io_uring.c:6971 > kthread+0x3af/0x4a0 kernel/kthread.c:292 > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296 > ================================================================== > Kernel panic - not syncing: panic_on_warn set ... > CPU: 1 PID: 26191 Comm: io_uring-sq Tainted: G B 5.10.0-rc1-next-20201030-syzkaller #0 > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 > Call Trace: > __dump_stack lib/dump_stack.c:77 [inline] > dump_stack+0x107/0x163 lib/dump_stack.c:118 > panic+0x306/0x73d kernel/panic.c:231 > end_report+0x58/0x5e mm/kasan/report.c:106 > __kasan_report mm/kasan/report.c:552 [inline] > kasan_report.cold+0xd/0x37 mm/kasan/report.c:562 > check_memory_region_inline mm/kasan/generic.c:186 [inline] > check_memory_region+0x13d/0x180 mm/kasan/generic.c:192 > instrument_atomic_read_write include/linux/instrumented.h:101 [inline] > atomic_inc include/asm-generic/atomic-instrumented.h:240 [inline] > mmgrab include/linux/sched/mm.h:36 [inline] > kthread_use_mm+0x11c/0x2a0 kernel/kthread.c:1257 > __io_sq_thread_acquire_mm fs/io_uring.c:1092 [inline] > __io_sq_thread_acquire_mm+0x1c4/0x220 fs/io_uring.c:1085 > io_sq_thread_acquire_mm_files.isra.0+0x125/0x180 fs/io_uring.c:1104 > io_init_req fs/io_uring.c:6661 [inline] > io_submit_sqes+0x89d/0x25f0 fs/io_uring.c:6757 > __io_sq_thread fs/io_uring.c:6904 [inline] > io_sq_thread+0x462/0x1630 fs/io_uring.c:6971 > kthread+0x3af/0x4a0 kernel/kthread.c:292 > ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296 > Kernel Offset: disabled > Rebooting in 86400 seconds.. I think this should fix it - we could _probably_ get by with a READ_ONCE() of the task mm for this case, but let's play it safe and lock down the task for a guaranteed consistent view of the current state. diff --git a/fs/io_uring.c b/fs/io_uring.c index dd2ee77feec6..610332f443bd 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -995,20 +995,33 @@ static void io_sq_thread_drop_mm(void) if (mm) { kthread_unuse_mm(mm); mmput(mm); + current->mm = NULL; } } static int __io_sq_thread_acquire_mm(struct io_ring_ctx *ctx) { - if (!current->mm) { - if (unlikely(!(ctx->flags & IORING_SETUP_SQPOLL) || - !ctx->sqo_task->mm || - !mmget_not_zero(ctx->sqo_task->mm))) - return -EFAULT; - kthread_use_mm(ctx->sqo_task->mm); + struct mm_struct *mm; + + if (current->mm) + return 0; + + /* Should never happen */ + if (unlikely(!(ctx->flags & IORING_SETUP_SQPOLL))) + return -EFAULT; + + task_lock(ctx->sqo_task); + mm = ctx->sqo_task->mm; + if (unlikely(!mm || !mmget_not_zero(mm))) + mm = NULL; + task_unlock(ctx->sqo_task); + + if (mm) { + kthread_use_mm(mm); + return 0; } - return 0; + return -EFAULT; } static int io_sq_thread_acquire_mm(struct io_ring_ctx *ctx, -- Jens Axboe
