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

[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+5a66db916cdde0dbcc1c@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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If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
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#syz undup

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

[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;
 	}
 }
--

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

[syzbot]

Hello,

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

Reported-by: syzbot+5a66db916cdde0dbcc1c@syzkaller.appspotmail.com
Tested-by: syzbot+5a66db916cdde0dbcc1c@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.

Forwarded: Test for 5a66db916cdde0dbcc1c

[syzbot]

For archival purposes, forwarding an incoming command email to
linux-kernel@vger.kernel.org.

***

Subject: Test for 5a66db916cdde0dbcc1c
Author: syoshida@redhat.com

#syz test

diff --git a/include/net/flow_offload.h b/include/net/flow_offload.h
index 596ab9791e4d..ff6d2bcb2cca 100644
--- a/include/net/flow_offload.h
+++ b/include/net/flow_offload.h
@@ -673,6 +673,8 @@ int flow_block_cb_setup_simple(struct flow_block_offload *f,
 			       flow_setup_cb_t *cb,
 			       void *cb_ident, void *cb_priv, bool ingress_only);
 
+void flow_block_cb_remove_driver(struct flow_block_cb *block_cb);
+
 enum flow_cls_command {
 	FLOW_CLS_REPLACE,
 	FLOW_CLS_DESTROY,
diff --git a/net/core/flow_offload.c b/net/core/flow_offload.c
index bc5169482710..137a44af5e1c 100644
--- a/net/core/flow_offload.c
+++ b/net/core/flow_offload.c
@@ -334,6 +334,8 @@ bool flow_block_cb_is_busy(flow_setup_cb_t *cb, void *cb_ident,
 }
 EXPORT_SYMBOL(flow_block_cb_is_busy);
 
+static DEFINE_MUTEX(flow_block_cb_list_lock);
+
 int flow_block_cb_setup_simple(struct flow_block_offload *f,
 			       struct list_head *driver_block_list,
 			       flow_setup_cb_t *cb,
@@ -341,6 +343,7 @@ int flow_block_cb_setup_simple(struct flow_block_offload *f,
 			       bool ingress_only)
 {
 	struct flow_block_cb *block_cb;
+	int err = 0;
 
 	if (ingress_only &&
 	    f->binder_type != FLOW_BLOCK_BINDER_TYPE_CLSACT_INGRESS)
@@ -348,32 +351,52 @@ int flow_block_cb_setup_simple(struct flow_block_offload *f,
 
 	f->driver_block_list = driver_block_list;
 
+	mutex_lock(&flow_block_cb_list_lock);
+
 	switch (f->command) {
 	case FLOW_BLOCK_BIND:
-		if (flow_block_cb_is_busy(cb, cb_ident, driver_block_list))
-			return -EBUSY;
+		if (flow_block_cb_is_busy(cb, cb_ident, driver_block_list)) {
+			err = -EBUSY;
+			break;
+		}
 
 		block_cb = flow_block_cb_alloc(cb, cb_ident, cb_priv, NULL);
-		if (IS_ERR(block_cb))
-			return PTR_ERR(block_cb);
+		if (IS_ERR(block_cb)) {
+			err = PTR_ERR(block_cb);
+			break;
+		}
 
 		flow_block_cb_add(block_cb, f);
 		list_add_tail(&block_cb->driver_list, driver_block_list);
-		return 0;
+		break;
 	case FLOW_BLOCK_UNBIND:
 		block_cb = flow_block_cb_lookup(f->block, cb, cb_ident);
-		if (!block_cb)
-			return -ENOENT;
+		if (!block_cb) {
+			err = -ENOENT;
+			break;
+		}
 
 		flow_block_cb_remove(block_cb, f);
 		list_del(&block_cb->driver_list);
-		return 0;
+		break;
 	default:
-		return -EOPNOTSUPP;
+		err = -EOPNOTSUPP;
+		break;
 	}
+
+	mutex_unlock(&flow_block_cb_list_lock);
+	return err;
 }
 EXPORT_SYMBOL(flow_block_cb_setup_simple);
 
+void flow_block_cb_remove_driver(struct flow_block_cb *block_cb)
+{
+	mutex_lock(&flow_block_cb_list_lock);
+	list_del(&block_cb->driver_list);
+	mutex_unlock(&flow_block_cb_list_lock);
+}
+EXPORT_SYMBOL(flow_block_cb_remove_driver);
+
 static DEFINE_MUTEX(flow_indr_block_lock);
 static LIST_HEAD(flow_block_indr_list);
 static LIST_HEAD(flow_block_indr_dev_list);
diff --git a/net/netfilter/nf_tables_offload.c b/net/netfilter/nf_tables_offload.c
index fd30e205de84..d60838bceafb 100644
--- a/net/netfilter/nf_tables_offload.c
+++ b/net/netfilter/nf_tables_offload.c
@@ -414,7 +414,7 @@ static void nft_indr_block_cleanup(struct flow_block_cb *block_cb)
 				    basechain, &extack);
 	nft_net = nft_pernet(net);
 	mutex_lock(&nft_net->commit_mutex);
-	list_del(&block_cb->driver_list);
+	flow_block_cb_remove_driver(block_cb);
 	list_move(&block_cb->list, &bo.cb_list);
 	nft_flow_offload_unbind(&bo, basechain);
 	mutex_unlock(&nft_net->commit_mutex);

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

[syzbot]

Hello,

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

Reported-by: syzbot+5a66db916cdde0dbcc1c@syzkaller.appspotmail.com
Tested-by: syzbot+5a66db916cdde0dbcc1c@syzkaller.appspotmail.com

Tested on:

commit:         ee924152 amd-xgbe: do not select NET_SELFTESTS when IN..
git tree:       net
console output: https://syzkaller.appspot.com/x/log.txt?x=17dc2b22580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=4b4258db89e7d927
dashboard link: https://syzkaller.appspot.com/bug?extid=5a66db916cdde0dbcc1c
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
patch:          https://syzkaller.appspot.com/x/patch.diff?x=15142b22580000

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