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

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Message-ID: <47165c76-d856-4c5d-bf2d-6d5a7fe08d43@linux.dev>
Date: Sat, 20 Dec 2025 18:55:32 +0000
From: Vadim Fedorenko <vadim.fedorenko@...ux.dev>
To: Daniel Gomez <da.gomez@...nel.org>, 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>,
 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: Re: [PATCH] bpf: crypto: replace -EEXIST with -EBUSY

On 20/12/2025 03:48, Daniel Gomez wrote:
> 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]

Even though I'm not quite sure that we should care once the core
module loader can adjust the error, the change looks ok to me:

Acked-by: Vadim Fedorenko <vadim.fedorenko@...ux.dev>