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Message-ID: <20260208110054.2525262-1-syoshida@redhat.com>
Date: Sun, 8 Feb 2026 20:00:50 +0900
From: Shigeru Yoshida <syoshida@...hat.com>
To: "David S. Miller" <davem@...emloft.net>,
Eric Dumazet <edumazet@...gle.com>,
Jakub Kicinski <kuba@...nel.org>,
Paolo Abeni <pabeni@...hat.com>,
Simon Horman <horms@...nel.org>,
Pablo Neira Ayuso <pablo@...filter.org>,
Florian Westphal <fw@...len.de>,
Phil Sutter <phil@....cc>,
Shigeru Yoshida <syoshida@...hat.com>
Cc: syzbot+5a66db916cdde0dbcc1c@...kaller.appspotmail.com,
netdev@...r.kernel.org,
linux-kernel@...r.kernel.org,
netfilter-devel@...r.kernel.org,
coreteam@...filter.org
Subject: [PATCH net] net: flow_offload: protect driver_block_list in flow_block_cb_setup_simple()
syzbot reported a list_del corruption in flow_block_cb_setup_simple(). [0]
flow_block_cb_setup_simple() accesses the driver_block_list (e.g.,
netdevsim's nsim_block_cb_list) without any synchronization. The
nftables offload path calls into this function via ndo_setup_tc while
holding the per-netns commit_mutex, but this mutex does not prevent
concurrent access from tasks in different network namespaces that
share the same driver_block_list, leading to list corruption:
- Task A (FLOW_BLOCK_BIND) calls list_add_tail() to insert a new
flow_block_cb into driver_block_list.
- Task B (FLOW_BLOCK_UNBIND) concurrently calls list_del() on another
flow_block_cb from the same list.
- The concurrent modifications corrupt the list pointers.
Fix this by adding a static mutex (flow_block_cb_list_lock) that
protects all driver_block_list operations within
flow_block_cb_setup_simple(). Also add a flow_block_cb_remove_driver()
helper for external callers that need to remove a block_cb from the
driver list under the same lock, and convert nft_indr_block_cleanup()
to use it.
[0]:
list_del corruption. prev->next should be ffff888028878200, but was ffffffff8e940fc0. (prev=ffffffff8e940fc0)
------------[ cut here ]------------
kernel BUG at lib/list_debug.c:64!
Oops: invalid opcode: 0000 [#1] SMP KASAN PTI
CPU: 1 UID: 0 PID: 6308 Comm: syz.3.231 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
[...]
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+0x293/0x660 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+0x675/0x8710 net/netfilter/nf_tables_api.c:10925
nfnetlink_rcv_batch net/netfilter/nfnetlink.c:576 [inline]
nfnetlink_rcv_skb_batch net/netfilter/nfnetlink.c:649 [inline]
nfnetlink_rcv+0x1ac9/0x2590 net/netfilter/nfnetlink.c:667
netlink_unicast_kernel net/netlink/af_netlink.c:1320 [inline]
netlink_unicast+0x82c/0x9e0 net/netlink/af_netlink.c:1346
netlink_sendmsg+0x805/0xb30 net/netlink/af_netlink.c:1896
sock_sendmsg_nosec net/socket.c:727 [inline]
__sock_sendmsg+0x219/0x270 net/socket.c:742
____sys_sendmsg+0x505/0x830 net/socket.c:2630
___sys_sendmsg+0x21f/0x2a0 net/socket.c:2684
__sys_sendmsg net/socket.c:2716 [inline]
__do_sys_sendmsg net/socket.c:2721 [inline]
__se_sys_sendmsg net/socket.c:2719 [inline]
__x64_sys_sendmsg+0x19b/0x260 net/socket.c:2719
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
Fixes: 955bcb6ea0df ("drivers: net: use flow block API")
Reported-by: syzbot+5a66db916cdde0dbcc1c@...kaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=5a66db916cdde0dbcc1c
Tested-by: syzbot+5a66db916cdde0dbcc1c@...kaller.appspotmail.com
Signed-off-by: Shigeru Yoshida <syoshida@...hat.com>
---
include/net/flow_offload.h | 2 ++
net/core/flow_offload.c | 41 ++++++++++++++++++++++++-------
net/netfilter/nf_tables_offload.c | 2 +-
3 files changed, 35 insertions(+), 10 deletions(-)
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);
--
2.52.0
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