Re: BUG: using smp_processor_id() in preemptible code in radix_tree_node_alloc

[Matthew Wilcox <willy@infradead.org>]

On Thu, Jun 04, 2020 at 08:55:55PM -0700, Eric Biggers wrote:
> Possibly a bug in lib/radix-tree.c?  this_cpu_ptr() in radix_tree_node_alloc()
> can be reached without a prior preempt_disable().  Or is the caller of
> idr_alloc() doing something wrong?

Yes, the idr_alloc() call is plainly wrong:

        mutex_lock(&qrtr_port_lock);
        if (!*port) {
                rc = idr_alloc(&qrtr_ports, ipc,
                               QRTR_MIN_EPH_SOCKET, QRTR_MAX_EPH_SOCKET + 1,
                               GFP_ATOMIC);

If we can take a mutex lock, there's no excuse to be using GFP_ATOMIC.
That (and the call slightly lower in the function) should be GFP_KERNEL
as the minimal fix (below).  I'll send a followup patch which converts
this IDR to the XArray instead.

diff --git a/net/qrtr/qrtr.c b/net/qrtr/qrtr.c
index 2d8d6131bc5f..d2547711d20c 100644
--- a/net/qrtr/qrtr.c
+++ b/net/qrtr/qrtr.c
@@ -692,15 +692,15 @@ static int qrtr_port_assign(struct qrtr_sock *ipc, int *port)
 	if (!*port) {
 		rc = idr_alloc(&qrtr_ports, ipc,
 			       QRTR_MIN_EPH_SOCKET, QRTR_MAX_EPH_SOCKET + 1,
-			       GFP_ATOMIC);
+			       GFP_KERNEL);
 		if (rc >= 0)
 			*port = rc;
 	} else if (*port < QRTR_MIN_EPH_SOCKET && !capable(CAP_NET_ADMIN)) {
 		rc = -EACCES;
 	} else if (*port == QRTR_PORT_CTRL) {
-		rc = idr_alloc(&qrtr_ports, ipc, 0, 1, GFP_ATOMIC);
+		rc = idr_alloc(&qrtr_ports, ipc, 0, 1, GFP_KERNEL);
 	} else {
-		rc = idr_alloc(&qrtr_ports, ipc, *port, *port + 1, GFP_ATOMIC);
+		rc = idr_alloc(&qrtr_ports, ipc, *port, *port + 1, GFP_KERNEL);
 		if (rc >= 0)
 			*port = rc;
 	}

> On Thu, Jun 04, 2020 at 07:02:18PM -0700, syzbot wrote:
> > Hello,
> > 
> > syzbot found the following crash on:
> > 
> > HEAD commit:    acf25aa6 Merge tag 'Smack-for-5.8' of git://github.com/csc..
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=13d6307a100000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=5263d9b5bce03c67
> > dashboard link: https://syzkaller.appspot.com/bug?extid=3eec59e770685e3dc879
> > compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> > syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=15bd4c1e100000
> > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1520c9de100000
> > 
> > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > Reported-by: syzbot+3eec59e770685e3dc879@syzkaller.appspotmail.com
> > 
> > RAX: ffffffffffffffda RBX: 00007ffdf01d56d0 RCX: 00000000004406c9
> > RDX: 0000000000000000 RSI: 0000000020000240 RDI: 0000000000000003
> > RBP: 0000000000000005 R08: 0000000000000001 R09: 0000000000000031
> > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000401f50
> > R13: 0000000000401fe0 R14: 0000000000000000 R15: 0000000000000000
> > BUG: using smp_processor_id() in preemptible [00000000] code: syz-executor036/6796
> > caller is radix_tree_node_alloc.constprop.0+0x200/0x330 lib/radix-tree.c:262
> > CPU: 0 PID: 6796 Comm: syz-executor036 Not tainted 5.7.0-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+0x188/0x20d lib/dump_stack.c:118
> >  check_preemption_disabled lib/smp_processor_id.c:47 [inline]
> >  debug_smp_processor_id.cold+0x88/0x9b lib/smp_processor_id.c:57
> >  radix_tree_node_alloc.constprop.0+0x200/0x330 lib/radix-tree.c:262
> >  radix_tree_extend+0x256/0x4e0 lib/radix-tree.c:424
> >  idr_get_free+0x60c/0x8e0 lib/radix-tree.c:1492
> >  idr_alloc_u32+0x170/0x2d0 lib/idr.c:46
> >  idr_alloc+0xc2/0x130 lib/idr.c:87
> >  qrtr_port_assign net/qrtr/qrtr.c:703 [inline]
> >  __qrtr_bind.isra.0+0x12e/0x5c0 net/qrtr/qrtr.c:756
> >  qrtr_autobind net/qrtr/qrtr.c:787 [inline]
> >  qrtr_autobind+0xaf/0xf0 net/qrtr/qrtr.c:775
> >  qrtr_sendmsg+0x1d6/0x770 net/qrtr/qrtr.c:895
> >  sock_sendmsg_nosec net/socket.c:652 [inline]
> >  sock_sendmsg+0xcf/0x120 net/socket.c:672
> >  ____sys_sendmsg+0x6e6/0x810 net/socket.c:2352
> >  ___sys_sendmsg+0x100/0x170 net/socket.c:2406
> >  __sys_sendmsg+0xe5/0x1b0 net/socket.c:2439
> >  do_syscall_64+0xf6/0x7d0 arch/x86/entry/common.c:295
> >  entry_SYSCALL_64_after_hwframe+0x49/0xb3
> > RIP: 0033:0x4406c9
> > Code: 25 02 00 85 c0 b8 00 00 00 00 48 0f 44 c3 5b c3 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 fb 13 fc ff c3 66 2e 0f 1f 84 00 00 00 00
> > RSP: 002b:00007ffdf01d56c8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
> > RAX: ffffffffffffffda RBX: 00007ffdf01d56d0 RCX: 00000000004406c9
> > RDX: 0000000000000000 RSI: 0000000020000240 RDI: 0000000000000003
> > RBP: 0000000000000005 R08: 0000000000000001 R09: 0000000000000031
> > R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000401f50
> > R13: 0000000000401fe0 R14: 0000000000000000 R15: 0000000000000000
> > 
> > 
> > ---
> > This bug is generated by a bot. It may contain errors.
> > See https://goo.gl/tpsmEJ for more information about syzbot.
> > syzbot engineers can be reached at syzkaller@googlegroups.com.
> > 
> > syzbot will keep track of this bug report. See:
> > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> > syzbot can test patches for this bug, for details see:
> > https://goo.gl/tpsmEJ#testing-patches
> >