[PATCH] KEYS: replace -EEXIST with -EBUSY

[Daniel Gomez <da.gomez@kernel.org>]

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:
  * pkcs8_key_parser x509_key_parser asymmetric_keys dns_resolver
  * nvme_keyring pkcs7_test_key rxrpc turris_signing_key

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]
---
 crypto/asymmetric_keys/asymmetric_type.c | 2 +-
 security/keys/key.c                      | 4 ++--
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/crypto/asymmetric_keys/asymmetric_type.c b/crypto/asymmetric_keys/asymmetric_type.c
index 348966ea2175..2c6f3a725102 100644
--- a/crypto/asymmetric_keys/asymmetric_type.c
+++ b/crypto/asymmetric_keys/asymmetric_type.c
@@ -634,7 +634,7 @@ int register_asymmetric_key_parser(struct asymmetric_key_parser *parser)
 		if (strcmp(cursor->name, parser->name) == 0) {
 			pr_err("Asymmetric key parser '%s' already registered\n",
 			       parser->name);
-			ret = -EEXIST;
+			ret = -EBUSY;
 			goto out;
 		}
 	}
diff --git a/security/keys/key.c b/security/keys/key.c
index 3bbdde778631..ed597660f72e 100644
--- a/security/keys/key.c
+++ b/security/keys/key.c
@@ -1219,7 +1219,7 @@ EXPORT_SYMBOL(generic_key_instantiate);
  *
  * Register a new key type.
  *
- * Returns 0 on success or -EEXIST if a type of this name already exists.
+ * Returns 0 on success or -EBUSY if a type of this name already exists.
  */
 int register_key_type(struct key_type *ktype)
 {
@@ -1228,7 +1228,7 @@ int register_key_type(struct key_type *ktype)
 
 	memset(&ktype->lock_class, 0, sizeof(ktype->lock_class));
 
-	ret = -EEXIST;
+	ret = -EBUSY;
 	down_write(&key_types_sem);
 
 	/* disallow key types with the same name */

---
base-commit: 8f0b4cce4481fb22653697cced8d0d04027cb1e8
change-id: 20251218-dev-module-init-eexists-keyring-5b008d7efb40

Best regards,
--  
Daniel Gomez <da.gomez@samsung.com>