On 10/13/19 8:49 PM, syzbot wrote: > Hello, > > syzbot found the following crash on: > > HEAD commit: 442630f6 Add linux-next specific files for 20191008 > git tree: linux-next > console output: https://syzkaller.appspot.com/x/log.txt?x=158fa6bf600000 > kernel config: https://syzkaller.appspot.com/x/.config?x=af1bfeef713eefdd > dashboard link: https://syzkaller.appspot.com/bug?extid=c0ba5b9e742f049a2edf > compiler: gcc (GCC) 9.0.0 20181231 (experimental) > syz repro: https://syzkaller.appspot.com/x/repro.syz?x=15a861b3600000 > C reproducer: https://syzkaller.appspot.com/x/repro.c?x=1769f48b600000 > > The bug was bisected to: > > commit 6c080ff07363389cb4092193eb333639f0392b8c > Author: Jens Axboe <axboe@xxxxxxxxx> > Date: Thu Oct 3 14:11:03 2019 +0000 > > io_uring: allow sparse fixed file sets > > bisection log: https://syzkaller.appspot.com/x/bisect.txt?x=1344b993600000 > final crash: https://syzkaller.appspot.com/x/report.txt?x=10c4b993600000 > console output: https://syzkaller.appspot.com/x/log.txt?x=1744b993600000 > > IMPORTANT: if you fix the bug, please add the following tag to the commit: > Reported-by: syzbot+c0ba5b9e742f049a2edf@xxxxxxxxxxxxxxxxxxxxxxxxx > Fixes: 6c080ff07363 ("io_uring: allow sparse fixed file sets") > > ------------[ cut here ]------------ > refcount_t: underflow; use-after-free. > WARNING: CPU: 0 PID: 8691 at lib/refcount.c:190 > refcount_sub_and_test_checked lib/refcount.c:190 [inline] > WARNING: CPU: 0 PID: 8691 at lib/refcount.c:190 > refcount_sub_and_test_checked+0x1d0/0x200 lib/refcount.c:180 > Kernel panic - not syncing: panic_on_warn set ... > CPU: 0 PID: 8691 Comm: syz-executor322 Not tainted 5.4.0-rc2-next-20191008 > #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 > panic+0x2e3/0x75c kernel/panic.c:221 > __warn.cold+0x2f/0x35 kernel/panic.c:582 > report_bug+0x289/0x300 lib/bug.c:195 > fixup_bug arch/x86/kernel/traps.c:174 [inline] > fixup_bug arch/x86/kernel/traps.c:169 [inline] > do_error_trap+0x11b/0x200 arch/x86/kernel/traps.c:267 > do_invalid_op+0x37/0x50 arch/x86/kernel/traps.c:286 > invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1028 > RIP: 0010:refcount_sub_and_test_checked lib/refcount.c:190 [inline] > RIP: 0010:refcount_sub_and_test_checked+0x1d0/0x200 lib/refcount.c:180 > Code: 1d b0 f0 7f 06 31 ff 89 de e8 6c d7 30 fe 84 db 75 94 e8 23 d6 30 fe > 48 c7 c7 20 81 e6 87 c6 05 90 f0 7f 06 01 e8 e8 15 02 fe <0f> 0b e9 75 ff > ff ff e8 04 d6 30 fe e9 6e ff ff ff 48 89 df e8 e7 > RSP: 0018:ffff8880a8267a28 EFLAGS: 00010282 > RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000 > RDX: 0000000000000000 RSI: ffffffff815cb676 RDI: ffffed101504cf37 > RBP: ffff8880a8267ac0 R08: ffff888090e363c0 R09: fffffbfff14eeb42 > R10: fffffbfff14eeb41 R11: ffffffff8a775a0f R12: 00000000fffffd02 > R13: 0000000000000001 R14: ffff8880a8267a98 R15: 0000000000000001 > sock_wfree+0x10c/0x190 net/core/sock.c:1958 > unix_destruct_scm+0x115/0x170 net/unix/scm.c:149 > io_destruct_skb+0x62/0x80 fs/io_uring.c:2995 > skb_release_head_state+0xeb/0x260 net/core/skbuff.c:652 > skb_release_all+0x16/0x60 net/core/skbuff.c:663 > __kfree_skb net/core/skbuff.c:679 [inline] > kfree_skb net/core/skbuff.c:697 [inline] > kfree_skb+0x101/0x3c0 net/core/skbuff.c:691 > __io_sqe_files_scm+0x429/0x640 fs/io_uring.c:3049 > io_sqe_files_scm fs/io_uring.c:3071 [inline] > io_sqe_files_register fs/io_uring.c:3154 [inline] > __io_uring_register+0x1f69/0x2d70 fs/io_uring.c:4152 > __do_sys_io_uring_register fs/io_uring.c:4204 [inline] > __se_sys_io_uring_register fs/io_uring.c:4186 [inline] > __x64_sys_io_uring_register+0x193/0x1f0 fs/io_uring.c:4186 > do_syscall_64+0xfa/0x760 arch/x86/entry/common.c:290 > entry_SYSCALL_64_after_hwframe+0x49/0xbe > RIP: 0033:0x440279 > Code: 18 89 d0 c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 00 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 fb 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00 > RSP: 002b:00007ffeeedc31e8 EFLAGS: 00000246 ORIG_RAX: 00000000000001ab > RAX: ffffffffffffffda RBX: 00000000004002c8 RCX: 0000000000440279 > RDX: 0000000020000280 RSI: 0000000000000002 RDI: 0000000000000003 > RBP: 00000000006ca018 R08: 0000000000000000 R09: 00000000004002c8 > R10: 0000000000000001 R11: 0000000000000246 R12: 0000000000401b00 > R13: 0000000000401b90 R14: 0000000000000000 R15: 0000000000000000 > Kernel Offset: disabled > Rebooting in 86400 seconds.. I think this will do it, but that's just from looking at the code, haven't tried to reproduce anything yet. I'll take a closer look tomorrow and verify. diff --git a/fs/io_uring.c b/fs/io_uring.c index 0b20b3599b01..52daeb71ee27 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -3016,7 +3016,6 @@ static int __io_sqe_files_scm(struct io_ring_ctx *ctx, int nr, int offset) } skb->sk = sk; - skb->destructor = io_destruct_skb; nr_files = 0; fpl->user = get_uid(ctx->user); @@ -3031,6 +3030,7 @@ static int __io_sqe_files_scm(struct io_ring_ctx *ctx, int nr, int offset) if (nr_files) { fpl->max = fpl->count = nr_files; UNIXCB(skb).fp = fpl; + skb->destructor = io_destruct_skb; refcount_add(skb->truesize, &sk->sk_wmem_alloc); skb_queue_head(&sk->sk_receive_queue, skb); -- Jens Axboe
