linux-kernel - [PATCH] bpf: crypto: replace -EEXIST with -EBUSY

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Message-Id: <20251220-dev-module-init-eexists-bpf-v1-1-7f186663dbe7@samsung.com>
Date: Sat, 20 Dec 2025 04:48:09 +0100
From: Daniel Gomez <da.gomez@...nel.org>
To: Vadim Fedorenko <vadim.fedorenko@...ux.dev>, 
 Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann <daniel@...earbox.net>, 
 Andrii Nakryiko <andrii@...nel.org>, 
 Martin KaFai Lau <martin.lau@...ux.dev>, 
 Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
 Yonghong Song <yonghong.song@...ux.dev>, 
 John Fastabend <john.fastabend@...il.com>, KP Singh <kpsingh@...nel.org>, 
 Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
 Jiri Olsa <jolsa@...nel.org>
Cc: Luis Chamberlain <mcgrof@...nel.org>, Petr Pavlu <petr.pavlu@...e.com>, 
 Daniel Gomez <da.gomez@...nel.org>, Sami Tolvanen <samitolvanen@...gle.com>, 
 Aaron Tomlin <atomlin@...mlin.com>, Lucas De Marchi <demarchi@...nel.org>, 
 bpf@...r.kernel.org, linux-modules@...r.kernel.org, 
 linux-kernel@...r.kernel.org, Daniel Gomez <da.gomez@...sung.com>
Subject: [PATCH] bpf: crypto: replace -EEXIST with -EBUSY

From: Daniel Gomez <da.gomez@...sung.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().

This affects bpf_crypto_skcipher module. While the configuration
required to build it as a module is unlikely in practice, it is
technically possible, so fix it for correctness.

Signed-off-by: Daniel Gomez <da.gomez@...sung.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]
---
 kernel/bpf/crypto.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/bpf/crypto.c b/kernel/bpf/crypto.c
index 83c4d9943084..1ab79a6dec84 100644
--- a/kernel/bpf/crypto.c
+++ b/kernel/bpf/crypto.c
@@ -60,7 +60,7 @@ struct bpf_crypto_ctx {
 int bpf_crypto_register_type(const struct bpf_crypto_type *type)
 {
 	struct bpf_crypto_type_list *node;
-	int err = -EEXIST;
+	int err = -EBUSY;

 	down_write(&bpf_crypto_types_sem);
 	list_for_each_entry(node, &bpf_crypto_types, list) {

---
base-commit: 8f0b4cce4481fb22653697cced8d0d04027cb1e8
change-id: 20251219-dev-module-init-eexists-bpf-da2aa3577437

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