net/bridge/netfilter/ebtables.c | 2 +- net/netfilter/nf_log.c | 4 ++-- net/netfilter/x_tables.c | 2 +- 3 files changed, 4 insertions(+), 4 deletions(-)
From: Daniel Gomez <da.gomez@samsung.com>
The -EEXIST error code is reserved by the module loading infrastructure
to indicate that a module is already loaded. When a module's init
function returns -EEXIST, userspace tools like kmod interpret this as
"module already loaded" and treat the operation as successful, returning
0 to the user even though the module initialization actually failed.
This follows the precedent set by commit 54416fd76770 ("netfilter:
conntrack: helper: Replace -EEXIST by -EBUSY") which fixed the same
issue in nf_conntrack_helper_register().
Affected modules:
* ebtable_broute ebtable_filter ebtable_nat arptable_filter
* ip6table_filter ip6table_mangle ip6table_nat ip6table_raw
* ip6table_security iptable_filter iptable_mangle iptable_nat
* iptable_raw iptable_security
Signed-off-by: Daniel Gomez <da.gomez@samsung.com>
---
The error code -EEXIST is reserved by the kernel module loader to
indicate that a module with the same name is already loaded. When a
module's init function returns -EEXIST, kmod interprets this as "module
already loaded" and reports success instead of failure [1].
The kernel module loader will include a safety net that provides -EEXIST
to -EBUSY with a warning [2], and a documentation patch has been sent to
prevent future occurrences [3].
These affected code paths were identified using a static analysis tool
[4] that traces -EEXIST returns to module_init(). The tool was developed
with AI assistance and all findings were manually validated.
Link: https://lore.kernel.org/all/aKEVQhJpRdiZSliu@orbyte.nwl.cc/ [1]
Link: https://lore.kernel.org/all/20251013-module-warn-ret-v1-0-ab65b41af01f@intel.com/ [2]
Link: https://lore.kernel.org/all/20251218-dev-module-init-eexists-modules-docs-v1-0-361569aa782a@samsung.com/ [3]
Link: https://gitlab.com/-/snippets/4913469 [4]
---
net/bridge/netfilter/ebtables.c | 2 +-
net/netfilter/nf_log.c | 4 ++--
net/netfilter/x_tables.c | 2 +-
3 files changed, 4 insertions(+), 4 deletions(-)
diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c
index 5697e3949a36..a04fc1757528 100644
--- a/net/bridge/netfilter/ebtables.c
+++ b/net/bridge/netfilter/ebtables.c
@@ -1299,7 +1299,7 @@ int ebt_register_template(const struct ebt_table *t, int (*table_init)(struct ne
list_for_each_entry(tmpl, &template_tables, list) {
if (WARN_ON_ONCE(strcmp(t->name, tmpl->name) == 0)) {
mutex_unlock(&ebt_mutex);
- return -EEXIST;
+ return -EBUSY;
}
}
diff --git a/net/netfilter/nf_log.c b/net/netfilter/nf_log.c
index 74cef8bf554c..62cf6a30875e 100644
--- a/net/netfilter/nf_log.c
+++ b/net/netfilter/nf_log.c
@@ -89,7 +89,7 @@ int nf_log_register(u_int8_t pf, struct nf_logger *logger)
if (pf == NFPROTO_UNSPEC) {
for (i = NFPROTO_UNSPEC; i < NFPROTO_NUMPROTO; i++) {
if (rcu_access_pointer(loggers[i][logger->type])) {
- ret = -EEXIST;
+ ret = -EBUSY;
goto unlock;
}
}
@@ -97,7 +97,7 @@ int nf_log_register(u_int8_t pf, struct nf_logger *logger)
rcu_assign_pointer(loggers[i][logger->type], logger);
} else {
if (rcu_access_pointer(loggers[pf][logger->type])) {
- ret = -EEXIST;
+ ret = -EBUSY;
goto unlock;
}
rcu_assign_pointer(loggers[pf][logger->type], logger);
diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
index 90b7630421c4..48105ea3df15 100644
--- a/net/netfilter/x_tables.c
+++ b/net/netfilter/x_tables.c
@@ -1764,7 +1764,7 @@ EXPORT_SYMBOL_GPL(xt_hook_ops_alloc);
int xt_register_template(const struct xt_table *table,
int (*table_init)(struct net *net))
{
- int ret = -EEXIST, af = table->af;
+ int ret = -EBUSY, af = table->af;
struct xt_template *t;
mutex_lock(&xt[af].mutex);
---
base-commit: 8f0b4cce4481fb22653697cced8d0d04027cb1e8
change-id: 20251218-dev-module-init-eexists-netfilter-56f4fb352dcb
Best regards,
--
Daniel Gomez <da.gomez@samsung.com>Daniel Gomez <da.gomez@kernel.org> wrote:
> From: Daniel Gomez <da.gomez@samsung.com>
>
> The -EEXIST error code is reserved by the module loading infrastructure
> to indicate that a module is already loaded. When a module's init
> function returns -EEXIST, userspace tools like kmod interpret this as
> "module already loaded" and treat the operation as successful, returning
> 0 to the user even though the module initialization actually failed.
>
> This follows the precedent set by commit 54416fd76770 ("netfilter:
> conntrack: helper: Replace -EEXIST by -EBUSY") which fixed the same
> issue in nf_conntrack_helper_register().
>
> Affected modules:
> * ebtable_broute ebtable_filter ebtable_nat arptable_filter
> * ip6table_filter ip6table_mangle ip6table_nat ip6table_raw
> * ip6table_security iptable_filter iptable_mangle iptable_nat
> * iptable_raw iptable_security
But this is very different from what 54416fd76770 fixes.
Before 54416fd76770. userspace can make a configuration entry that
prevents and unrelated module from getting loaded but at the same time
it doesn't provide any error to userspace.
All these -EEXIST should not be possible unless the module is
already loaded.
> diff --git a/net/bridge/netfilter/ebtables.c b/net/bridge/netfilter/ebtables.c
> index 5697e3949a36..a04fc1757528 100644
> --- a/net/bridge/netfilter/ebtables.c
> +++ b/net/bridge/netfilter/ebtables.c
> @@ -1299,7 +1299,7 @@ int ebt_register_template(const struct ebt_table *t, int (*table_init)(struct ne
> list_for_each_entry(tmpl, &template_tables, list) {
> if (WARN_ON_ONCE(strcmp(t->name, tmpl->name) == 0)) {
> mutex_unlock(&ebt_mutex);
> - return -EEXIST;
> + return -EBUSY;
As you can see from the WARN_ON, this cannot happen unless someone adds a new ebt kernel
table module that tries to register the same name.
> diff --git a/net/netfilter/nf_log.c b/net/netfilter/nf_log.c
> index 74cef8bf554c..62cf6a30875e 100644
> --- a/net/netfilter/nf_log.c
> +++ b/net/netfilter/nf_log.c
> @@ -89,7 +89,7 @@ int nf_log_register(u_int8_t pf, struct nf_logger *logger)
> if (pf == NFPROTO_UNSPEC) {
> for (i = NFPROTO_UNSPEC; i < NFPROTO_NUMPROTO; i++) {
> if (rcu_access_pointer(loggers[i][logger->type])) {
> - ret = -EEXIST;
> + ret = -EBUSY;
> goto unlock;
I don't see how this can happen, unless someone adds a new kernel module
that claims the same type as an existing kernel module.
> diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c
> index 90b7630421c4..48105ea3df15 100644
> --- a/net/netfilter/x_tables.c
> +++ b/net/netfilter/x_tables.c
> @@ -1764,7 +1764,7 @@ EXPORT_SYMBOL_GPL(xt_hook_ops_alloc);
> int xt_register_template(const struct xt_table *table,
> int (*table_init)(struct net *net))
> {
> - int ret = -EEXIST, af = table->af;
> + int ret = -EBUSY, af = table->af;
> struct xt_template *t;
Same, this requires someone adding a new kernel module with clashing
name.
I'll apply this patch but its not related to 54416fd76770 afaics.
On 19/12/2025 08.48, Florian Westphal wrote:
> Daniel Gomez <da.gomez@kernel.org> wrote:
>> From: Daniel Gomez <da.gomez@samsung.com>
>>
>> The -EEXIST error code is reserved by the module loading infrastructure
>> to indicate that a module is already loaded. When a module's init
>> function returns -EEXIST, userspace tools like kmod interpret this as
>> "module already loaded" and treat the operation as successful, returning
>> 0 to the user even though the module initialization actually failed.
>>
>> This follows the precedent set by commit 54416fd76770 ("netfilter:
>> conntrack: helper: Replace -EEXIST by -EBUSY") which fixed the same
>> issue in nf_conntrack_helper_register().
>>
>> Affected modules:
>> * ebtable_broute ebtable_filter ebtable_nat arptable_filter
>> * ip6table_filter ip6table_mangle ip6table_nat ip6table_raw
>> * ip6table_security iptable_filter iptable_mangle iptable_nat
>> * iptable_raw iptable_security
>
> But this is very different from what 54416fd76770 fixes.
>
> Before 54416fd76770. userspace can make a configuration entry that
> prevents and unrelated module from getting loaded but at the same time
> it doesn't provide any error to userspace.
>
> All these -EEXIST should not be possible unless the module is
> already loaded.
I see.
> I'll apply this patch but its not related to 54416fd76770 afaics.
Thanks.
Then, what about removing that paragraph that mentions the commit and add
something like:
Replace -EEXIST with -EBUSY to ensure correct error reporting in the module
initialization path.
Daniel Gomez <da.gomez@kernel.org> wrote: > something like: > > Replace -EEXIST with -EBUSY to ensure correct error reporting in the module > initialization path. Makes sense, I will mangle it locally when I apply this. Thanks!
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