[syzbot] [net?] WARNING in netdev_queue_get_dma_dev

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 075b74841bd0 Linux 7.2-rc6
git tree: upstream
console+strace: https://syzkaller.appspot.com/x/log.txt?x=176a7db9580000
kernel config: https://syzkaller.appspot.com/x/.config?x=145fa60d73086782
dashboard link: https://syzkaller.appspot.com/bug?extid=a78926bdac2adb52dc0e
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16225db9580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17bade32580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/1dc04730d019/disk-075b7484.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/d76da42271f4/vmlinux-075b7484.xz
kernel image: https://storage.googleapis.com/syzbot-assets/07b1cdbcbe45/bzImage-075b7484.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a78926...@syzkaller.appspotmail.com

------------[ cut here ]------------
RTNL: assertion failed at ./include/net/netdev_lock.h (72)
WARNING: ./include/net/netdev_lock.h:72 at netdev_assert_locked_ops_compat include/net/netdev_lock.h:72 [inline], CPU#1: syz-executor223/5620
WARNING: ./include/net/netdev_lock.h:72 at netdev_queue_get_dma_dev+0x52e/0x660 net/core/netdev_queues.c:43, CPU#1: syz-executor223/5620
Modules linked in:
CPU: 1 UID: 0 PID: 5620 Comm: syz-executor223 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/16/2026
RIP: 0010:netdev_assert_locked_ops_compat include/net/netdev_lock.h:72 [inline]
RIP: 0010:netdev_queue_get_dma_dev+0x53a/0x660 net/core/netdev_queues.c:43
Code: 89 c5 89 c6 e8 27 f7 68 f8 45 85 ed 0f 85 be fb ff ff e8 a9 fc 68 f8 48 8d 3d 12 0e 90 07 ba 48 00 00 00 48 c7 c6 a0 88 18 8d <67> 48 0f b9 3a e9 9c fb ff ff e8 87 fc 68 f8 48 8d bd 00 08 00 00
RSP: 0018:ffffc90003b47a80 EFLAGS: 00010293
RAX: 0000000000000000 RBX: ffff888029874000 RCX: ffffffff89a16569
RDX: 0000000000000048 RSI: ffffffff8d1888a0 RDI: ffffffff91317390
RBP: 0000000000000000 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000000
R13: 0000000000000000 R14: ffff88807b3f2568 R15: ffffc90003b47be0
FS: 00005555885ac400(0000) GS:ffff888123ed8000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000001000 CR3: 000000006f8b6000 CR4: 00000000003526f0
Call Trace:
<TASK>
zcrx_register_netdev io_uring/zcrx.c:831 [inline]
io_register_zcrx+0xe94/0x1d30 io_uring/zcrx.c:983
__io_uring_register io_uring/register.c:942 [inline]
__do_sys_io_uring_register+0x1193/0x1bc0 io_uring/register.c:1040
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fd0b54bbcb9
Code: c0 79 93 eb d5 48 8d 7c 1d 00 eb 99 0f 1f 44 00 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 73 01 c3 48 c7 c1 d8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffe25f0a7f8 EFLAGS: 00000246 ORIG_RAX: 00000000000001ab
RAX: ffffffffffffffda RBX: 00007ffe25f0a928 RCX: 00007fd0b54bbcb9
RDX: 0000200000000400 RSI: 0000000000000020 RDI: 0000000000000003
RBP: 0000000000000001 R08: 0000000000000000 R09: 00007ffe25f0a928
R10: 0000000000000001 R11: 0000000000000246 R12: 00007ffe25f0a918
R13: 0000000000000002 R14: 00007fd0b554cca0 R15: 0000000000000002
</TASK>
----------------
Code disassembly (best guess):
0: 89 c5 mov %eax,%ebp
2: 89 c6 mov %eax,%esi
4: e8 27 f7 68 f8 call 0xf868f730
9: 45 85 ed test %r13d,%r13d
c: 0f 85 be fb ff ff jne 0xfffffbd0
12: e8 a9 fc 68 f8 call 0xf868fcc0
17: 48 8d 3d 12 0e 90 07 lea 0x7900e12(%rip),%rdi # 0x7900e30
1e: ba 48 00 00 00 mov $0x48,%edx
23: 48 c7 c6 a0 88 18 8d mov $0xffffffff8d1888a0,%rsi
* 2a: 67 48 0f b9 3a ud1 (%edx),%rdi <-- trapping instruction
2f: e9 9c fb ff ff jmp 0xfffffbd0
34: e8 87 fc 68 f8 call 0xf868fcc0
39: 48 8d bd 00 08 00 00 lea 0x800(%rbp),%rdi


---
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[Jakub Kicinski]

Hi Pavel, could you TAL?

[Pavel Begunkov]

On 8/4/26 22:00, Jakub Kicinski wrote:
> Hi Pavel, could you TAL?

It complains on not holding rtnl, so the netdev should be not
qops-enabled, and we acquire it with netdev_get_by_index_lock().
It's going to be rejected later, but not sure whether netdev->lock
protects its device and leasing logic well in this case.

As a quick fix, let's fail it early in zcrx if there is no qops.

--
Pavel Begunkov

[pavankuma...@gmail.com]

From: Yalagada Pavan Kumar <pavankuma...@gmail.com>

zcrx registration can fail for netdevices that do not support the
required ops locking model.

netdev_queue_get_dma_dev() requires ops locking support.
Calling it for devices without ops lock support triggers
netdev_assert_locked_ops_compat().

Check netdev_need_ops_lock() before accessing queue DMA information
and return -EOPNOTSUPP for unsupported devices.

Reported-by: syzbot+a78926...@syzkaller.appspotmail.com
Link: https://syzkaller.appspot.com/bug?extid=a78926bdac2adb52dc0e
Signed-off-by: Yalagada Pavan Kumar <pavankuma...@gmail.com>

---
Testing:
- Verified the reported reproducer in a VM.
---
io_uring/zcrx.c | 10 ++++++++++
1 file changed, 10 insertions(+)

diff --git a/io_uring/zcrx.c b/io_uring/zcrx.c
index f1464ea8ca64..2eba7d4e4483 100644
--- a/io_uring/zcrx.c
+++ b/io_uring/zcrx.c
@@ -17,6 +17,7 @@
#include <net/netdev_rx_queue.h>
#include <net/tcp.h>
#include <net/rps.h>
+#include <net/netdev_lock.h>

#include <trace/events/page_pool.h>

@@ -828,6 +829,15 @@ static int zcrx_register_netdev(struct io_zcrx_ifq *ifq,

netdev_hold(ifq->netdev, &ifq->netdev_tracker, GFP_KERNEL);

+ /*
+ * netdev_queue_get_dma_dev() requires the netdev ops locking
+ * model. Reject devices which do not support it.
+ */
+ if (!netdev_need_ops_lock(ifq->netdev)) {
+ ret = -EOPNOTSUPP;
+ goto netdev_put_unlock;
+ }
+
ifq->dev = netdev_queue_get_dma_dev(ifq->netdev, if_rxq, NETDEV_QUEUE_TYPE_RX);
if (!ifq->dev) {
ret = -EOPNOTSUPP;
--
2.43.0