linux-kernel - Re: [PATCH 1/5] module: Prevent silent truncation of module name in delete

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Message-ID: <0dee8b80-1bb9-4d34-9b39-344e391d56f4@kernel.org>
Date: Wed, 16 Jul 2025 21:47:19 +0200
From: Daniel Gomez <da.gomez@...nel.org>
To: Petr Pavlu <petr.pavlu@...e.com>, Luis Chamberlain <mcgrof@...nel.org>,
 Sami Tolvanen <samitolvanen@...gle.com>, Daniel Gomez <da.gomez@...sung.com>
Cc: linux-modules@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/5] module: Prevent silent truncation of module name in
 delete_module(2)

On 30/06/2025 16.32, Petr Pavlu wrote:
> Passing a module name longer than MODULE_NAME_LEN to the delete_module
> syscall results in its silent truncation. This really isn't much of
> a problem in practice, but it could theoretically lead to the removal of an
> incorrect module. It is more sensible to return ENAMETOOLONG or ENOENT in
> such a case.
> 
> Update the syscall to return ENOENT, as documented in the delete_module(2)
> man page to mean "No module by that name exists." This is appropriate
> because a module with a name

Including the NUL byte...

> longer than MODULE_NAME_LEN cannot be loaded
> in the first place.
> 
> Signed-off-by: Petr Pavlu <petr.pavlu@...e.com>
> ---
>  kernel/module/main.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/kernel/module/main.c b/kernel/module/main.c
> index 413ac6ea3702..933a9854cb7d 100644
> --- a/kernel/module/main.c
> +++ b/kernel/module/main.c
> @@ -751,14 +751,16 @@ SYSCALL_DEFINE2(delete_module, const char __user *, name_user,
>  	struct module *mod;
>  	char name[MODULE_NAME_LEN];
>  	char buf[MODULE_FLAGS_BUF_SIZE];
> -	int ret, forced = 0;
> +	int ret, len, forced = 0;
>  
>  	if (!capable(CAP_SYS_MODULE) || modules_disabled)
>  		return -EPERM;
>  
> -	if (strncpy_from_user(name, name_user, MODULE_NAME_LEN-1) < 0)
> -		return -EFAULT;
> -	name[MODULE_NAME_LEN-1] = '\0';
> +	len = strncpy_from_user(name, name_user, MODULE_NAME_LEN);
> +	if (len == 0 || len == MODULE_NAME_LEN)
> +		return -ENOENT;
> +	if (len < 0)
> +		return len;

This looks correct to me. The new code not only returns the correct errors
indicated in delete_module(2) but also checks for the case user passes an
empty string and the case where NUL char is not found when copying (with len
== MODULE_NAME_LEN) as well as it's using the correct length (MODULE_NAME_LEN)
for copying.

Reviewed-by: Daniel Gomez <da.gomez@...sung.com>