On 10/28/19 1:22 AM, syzbot wrote: > Hello, > > syzbot found the following crash on: > > HEAD commit: 5a1e843c Merge tag 'mips_fixes_5.4_3' of git://git.kernel... > git tree: upstream > console output: https://syzkaller.appspot.com/x/log.txt?x=10e2001f600000 > kernel config: https://syzkaller.appspot.com/x/.config?x=420126a10fdda0f1 > dashboard link: https://syzkaller.appspot.com/bug?extid=6f03d895a6cd0d06187f > compiler: gcc (GCC) 9.0.0 20181231 (experimental) > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=11d4fa97600000 > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > Reported-by: syzbot+6f03d895a6cd0d06187f@xxxxxxxxxxxxxxxxxxxxxxxxx > > ================================================================== > BUG: KASAN: use-after-free in io_uring_create fs/io_uring.c:3842 [inline] > BUG: KASAN: use-after-free in io_uring_setup+0x1877/0x18c0 > fs/io_uring.c:3881 > Read of size 8 at addr ffff888082284048 by task syz-executor.5/11342 > > CPU: 1 PID: 11342 Comm: syz-executor.5 Not tainted 5.4.0-rc4+ #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+0x172/0x1f0 lib/dump_stack.c:113 > print_address_description.constprop.0.cold+0xd4/0x30b mm/kasan/report.c:374 > __kasan_report.cold+0x1b/0x41 mm/kasan/report.c:506 > kasan_report+0x12/0x20 mm/kasan/common.c:634 > __asan_report_load8_noabort+0x14/0x20 mm/kasan/generic_report.c:132 > io_uring_create fs/io_uring.c:3842 [inline] > io_uring_setup+0x1877/0x18c0 fs/io_uring.c:3881 > __do_sys_io_uring_setup fs/io_uring.c:3894 [inline] > __se_sys_io_uring_setup fs/io_uring.c:3891 [inline] > __x64_sys_io_uring_setup+0x54/0x80 fs/io_uring.c:3891 > do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > RIP: 0033:0x459f39 > Code: ad b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 > 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff > ff 0f 83 7b b6 fb ff c3 66 2e 0f 1f 84 00 00 00 00 > RSP: 002b:00007f313e126c78 EFLAGS: 00000246 ORIG_RAX: 00000000000001a9 > RAX: ffffffffffffffda RBX: 0000000000000002 RCX: 0000000000459f39 > RDX: 0000000000000000 RSI: 00000000200005c0 RDI: 000000040000000e > RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000 > R10: 0000000000000000 R11: 0000000000000246 R12: 00007f313e1276d4 > R13: 00000000004c1512 R14: 00000000004d4da8 R15: 00000000ffffffff > > Allocated by task 11342: > save_stack+0x23/0x90 mm/kasan/common.c:69 > set_track mm/kasan/common.c:77 [inline] > __kasan_kmalloc mm/kasan/common.c:510 [inline] > __kasan_kmalloc.constprop.0+0xcf/0xe0 mm/kasan/common.c:483 > kasan_kmalloc+0x9/0x10 mm/kasan/common.c:524 > kmem_cache_alloc_trace+0x158/0x790 mm/slab.c:3550 > kmalloc include/linux/slab.h:556 [inline] > kzalloc include/linux/slab.h:690 [inline] > io_ring_ctx_alloc fs/io_uring.c:393 [inline] > io_uring_create fs/io_uring.c:3811 [inline] > io_uring_setup+0xec6/0x18c0 fs/io_uring.c:3881 > __do_sys_io_uring_setup fs/io_uring.c:3894 [inline] > __se_sys_io_uring_setup fs/io_uring.c:3891 [inline] > __x64_sys_io_uring_setup+0x54/0x80 fs/io_uring.c:3891 > do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > Freed by task 11335: > save_stack+0x23/0x90 mm/kasan/common.c:69 > set_track mm/kasan/common.c:77 [inline] > kasan_set_free_info mm/kasan/common.c:332 [inline] > __kasan_slab_free+0x102/0x150 mm/kasan/common.c:471 > kasan_slab_free+0xe/0x10 mm/kasan/common.c:480 > __cache_free mm/slab.c:3425 [inline] > kfree+0x10a/0x2c0 mm/slab.c:3756 > io_ring_ctx_free fs/io_uring.c:3552 [inline] > io_ring_ctx_wait_and_kill+0x4d7/0x6c0 fs/io_uring.c:3592 > io_uring_release+0x42/0x50 fs/io_uring.c:3600 > __fput+0x2ff/0x890 fs/file_table.c:280 > ____fput+0x16/0x20 fs/file_table.c:313 > task_work_run+0x145/0x1c0 kernel/task_work.c:113 > tracehook_notify_resume include/linux/tracehook.h:188 [inline] > exit_to_usermode_loop+0x316/0x380 arch/x86/entry/common.c:163 > prepare_exit_to_usermode arch/x86/entry/common.c:194 [inline] > syscall_return_slowpath arch/x86/entry/common.c:274 [inline] > do_syscall_64+0x65f/0x760 arch/x86/entry/common.c:300 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > > The buggy address belongs to the object at ffff888082284000 > which belongs to the cache kmalloc-2k of size 2048 > The buggy address is located 72 bytes inside of > 2048-byte region [ffff888082284000, ffff888082284800) > The buggy address belongs to the page: > page:ffffea000208a100 refcount:1 mapcount:0 mapping:ffff8880aa400e00 > index:0x0 > flags: 0x1fffc0000000200(slab) > raw: 01fffc0000000200 ffffea0002a1bc88 ffffea00023fa248 ffff8880aa400e00 > raw: 0000000000000000 ffff888082284000 0000000100000001 0000000000000000 > page dumped because: kasan: bad access detected > > Memory state around the buggy address: > ffff888082283f00: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc > ffff888082283f80: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc >> ffff888082284000: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > ^ > ffff888082284080: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > ffff888082284100: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb > ================================================================== Interesting, looks like a malicious case that attempts to close the fd as soon as it's installed. As a result of that, the rest of the setup will be done on a ring that's already torn down. The below should fix that. Totally untested, haven't tried the reproducer yet. diff --git a/fs/io_uring.c b/fs/io_uring.c index ba1431046c98..749637ca9cf7 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -3821,6 +3821,12 @@ static int io_uring_create(unsigned entries, struct io_uring_params *p) ctx->account_mem = account_mem; ctx->user = user; + /* + * Grab an initial reference to the ctx, so we ensure we have one + * by the time the fd is installed. + */ + percpu_ref_get(&ctx->refs); + ret = io_allocate_scq_urings(ctx, p); if (ret) goto err; @@ -3851,8 +3857,10 @@ static int io_uring_create(unsigned entries, struct io_uring_params *p) p->cq_off.cqes = offsetof(struct io_rings, cqes); p->features = IORING_FEAT_SINGLE_MMAP; + percpu_ref_put(&ctx->refs); return ret; err: + percpu_ref_put(&ctx->refs); io_ring_ctx_wait_and_kill(ctx); return ret; } -- Jens Axboe
