[syzbot] [net?] BUG: corrupted list in flow_block_cb_setup_simple

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: e59a039119c3 Merge tag 's390-6.17-4' of git://git.kernel.o..
git tree: bpf
console output: https://syzkaller.appspot.com/x/log.txt?x=1523e934580000
kernel config: https://syzkaller.appspot.com/x/.config?x=4d8792ecb6308d0f
dashboard link: https://syzkaller.appspot.com/bug?extid=5a66db916cdde0dbcc1c
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16d4bd62580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10d69642580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/324da524bbd8/disk-e59a0391.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/0fa38e1d54f4/vmlinux-e59a0391.xz
kernel image: https://storage.googleapis.com/syzbot-assets/b1ea8074daa0/bzImage-e59a0391.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5a66db...@syzkaller.appspotmail.com

non-slab/vmalloc memory
list_del corruption. prev->next should be ffff888077fdb100, but was ffffffff8edac9a0. (prev=ffffffff8edac9a0)
------------[ cut here ]------------
kernel BUG at lib/list_debug.c:64!
Oops: invalid opcode: 0000 [#1] SMP KASAN PTI
CPU: 0 UID: 0 PID: 6449 Comm: syz.3.301 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 08/18/2025
RIP: 0010:__list_del_entry_valid_or_report+0x15a/0x190 lib/list_debug.c:62
Code: e8 4b a5 31 fd 43 80 3c 2c 00 74 08 4c 89 ff e8 1c 9d 52 fd 49 8b 17 48 c7 c7 a0 40 e3 8b 48 89 de 4c 89 f9 e8 07 0b 57 fc 90 <0f> 0b 4c 89 f7 e8 1c a5 31 fd 43 80 3c 2c 00 74 08 4c 89 ff e8 ed
RSP: 0018:ffffc90003f4e760 EFLAGS: 00010246
RAX: 000000000000006d RBX: ffff888077fdb100 RCX: 21dc4908dd936700
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: 1ffff920007e9d3e R08: ffffc90003f4e487 R09: 1ffff920007e9c90
R10: dffffc0000000000 R11: fffff520007e9c91 R12: 1ffffffff1db5934
R13: dffffc0000000000 R14: ffffffff8edac9a0 R15: ffffffff8edac9a0
FS: 00005555769e1500(0000) GS:ffff888125c15000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000380 CR3: 0000000030806000 CR4: 00000000003526f0
Call Trace:
<TASK>
__list_del_entry_valid include/linux/list.h:124 [inline]
__list_del_entry include/linux/list.h:215 [inline]
list_del include/linux/list.h:229 [inline]
flow_block_cb_setup_simple+0x62d/0x740 net/core/flow_offload.c:369
nft_block_offload_cmd net/netfilter/nf_tables_offload.c:397 [inline]
nft_chain_offload_cmd+0x290/0x660 net/netfilter/nf_tables_offload.c:451
nft_flow_block_chain net/netfilter/nf_tables_offload.c:471 [inline]
nft_flow_offload_chain net/netfilter/nf_tables_offload.c:513 [inline]
nft_flow_rule_offload_commit+0x40d/0x1b60 net/netfilter/nf_tables_offload.c:592
nf_tables_commit+0x675/0x8700 net/netfilter/nf_tables_api.c:10933
nfnetlink_rcv_batch net/netfilter/nfnetlink.c:574 [inline]
nfnetlink_rcv_skb_batch net/netfilter/nfnetlink.c:647 [inline]
nfnetlink_rcv+0x1a4e/0x2520 net/netfilter/nfnetlink.c:665
netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
netlink_unicast+0x82f/0x9e0 net/netlink/af_netlink.c:1346
netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1896
sock_sendmsg_nosec net/socket.c:714 [inline]
__sock_sendmsg+0x219/0x270 net/socket.c:729
____sys_sendmsg+0x505/0x830 net/socket.c:2614
___sys_sendmsg+0x21f/0x2a0 net/socket.c:2668
__sys_sendmsg net/socket.c:2700 [inline]
__do_sys_sendmsg net/socket.c:2705 [inline]
__se_sys_sendmsg net/socket.c:2703 [inline]
__x64_sys_sendmsg+0x19b/0x260 net/socket.c:2703
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0x3b0 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fe1b0d8eba9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffc23fb3798 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00007fe1b0fd5fa0 RCX: 00007fe1b0d8eba9
RDX: 000000000000c050 RSI: 0000200000000cc0 RDI: 0000000000000003
RBP: 00007fe1b0e11e19 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007fe1b0fd5fa0 R14: 00007fe1b0fd5fa0 R15: 0000000000000003
</TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:__list_del_entry_valid_or_report+0x15a/0x190 lib/list_debug.c:62
Code: e8 4b a5 31 fd 43 80 3c 2c 00 74 08 4c 89 ff e8 1c 9d 52 fd 49 8b 17 48 c7 c7 a0 40 e3 8b 48 89 de 4c 89 f9 e8 07 0b 57 fc 90 <0f> 0b 4c 89 f7 e8 1c a5 31 fd 43 80 3c 2c 00 74 08 4c 89 ff e8 ed
RSP: 0018:ffffc90003f4e760 EFLAGS: 00010246
RAX: 000000000000006d RBX: ffff888077fdb100 RCX: 21dc4908dd936700
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: 1ffff920007e9d3e R08: ffffc90003f4e487 R09: 1ffff920007e9c90
R10: dffffc0000000000 R11: fffff520007e9c91 R12: 1ffffffff1db5934
R13: dffffc0000000000 R14: ffffffff8edac9a0 R15: ffffffff8edac9a0
FS: 00005555769e1500(0000) GS:ffff888125c15000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000200000000380 CR3: 0000000030806000 CR4: 00000000003526f0


---
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[Hillf Danton]

> Date: Fri, 12 Sep 2025 00:06:29 -0700 [thread overview]

> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: e59a039119c3 Merge tag 's390-6.17-4' of git://git.kernel.o..
> git tree: bpf
> console output: https://syzkaller.appspot.com/x/log.txt?x=1523e934580000
> kernel config: https://syzkaller.appspot.com/x/.config?x=4d8792ecb6308d0f
> dashboard link: https://syzkaller.appspot.com/bug?extid=5a66db916cdde0dbcc1c
> compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=16d4bd62580000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=10d69642580000

#syz test upstream master

--- x/net/core/flow_offload.c
+++ y/net/core/flow_offload.c
@@ -334,6 +334,7 @@ bool flow_block_cb_is_busy(flow_setup_cb
}
EXPORT_SYMBOL(flow_block_cb_is_busy);

+static DEFINE_MUTEX(setup_lock);
int flow_block_cb_setup_simple(struct flow_block_offload *f,
struct list_head *driver_block_list,
flow_setup_cb_t *cb,
@@ -348,27 +349,37 @@ int flow_block_cb_setup_simple(struct fl

f->driver_block_list = driver_block_list;

+ mutex_lock(&setup_lock);
switch (f->command) {
case FLOW_BLOCK_BIND:
- if (flow_block_cb_is_busy(cb, cb_ident, driver_block_list))
+ if (flow_block_cb_is_busy(cb, cb_ident, driver_block_list)) {
+ mutex_unlock(&setup_lock);
return -EBUSY;
+ }

block_cb = flow_block_cb_alloc(cb, cb_ident, cb_priv, NULL);
- if (IS_ERR(block_cb))
+ if (IS_ERR(block_cb)) {
+ mutex_unlock(&setup_lock);
return PTR_ERR(block_cb);
+ }

flow_block_cb_add(block_cb, f);
list_add_tail(&block_cb->driver_list, driver_block_list);
+ mutex_unlock(&setup_lock);
return 0;
case FLOW_BLOCK_UNBIND:
block_cb = flow_block_cb_lookup(f->block, cb, cb_ident);
- if (!block_cb)
+ if (!block_cb) {
+ mutex_unlock(&setup_lock);
return -ENOENT;
+ }

flow_block_cb_remove(block_cb, f);
list_del(&block_cb->driver_list);
+ mutex_unlock(&setup_lock);
return 0;
default:
+ mutex_unlock(&setup_lock);
return -EOPNOTSUPP;
}
}
--

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+5a66db...@syzkaller.appspotmail.com
Tested-by: syzbot+5a66db...@syzkaller.appspotmail.com

Tested on:

commit: 320475fb Merge tag 'mtd/fixes-for-6.17-rc6' of git://g..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1236eb12580000

kernel config: https://syzkaller.appspot.com/x/.config?x=4d8792ecb6308d0f
dashboard link: https://syzkaller.appspot.com/bug?extid=5a66db916cdde0dbcc1c
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

patch: https://syzkaller.appspot.com/x/patch.diff?x=148cb362580000

Note: testing is done by a robot and is best-effort only.