linux-kernel - Re: [PATCH 1/2] module: Fix memory deallocation on error path in move

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Message-ID: <f6fa3df3-38d5-4191-96d1-9a8a2152cedf@suse.com>
Date: Sun, 8 Jun 2025 09:25:34 +0200
From: Petr Pavlu <petr.pavlu@...e.com>
To: 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 1/2] module: Fix memory deallocation on error path in
 move_module()

On 6/7/25 6:16 PM, Petr Pavlu wrote:
> The function move_module() uses the variable t to track how many memory
> types it has allocated and consequently how many should be freed if an
> error occurs.
> 
> The variable is initially set to 0 and is updated when a call to
> module_memory_alloc() fails. However, move_module() can fail for other
> reasons as well, in which case t remains set to 0 and no memory is freed.
> 
> Fix the problem by setting t to MOD_MEM_NUM_TYPES after all memory types
> have been allocated. Additionally, make the deallocation loop more robust
> by not relying on the mod_mem_type_t enum having a signed integer as its
> underlying type.
> 
> Fixes: c7ee8aebf6c0 ("module: add stop-grap sanity check on module memcpy()")
> Signed-off-by: Petr Pavlu <petr.pavlu@...e.com>
> ---
>  kernel/module/main.c | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/kernel/module/main.c b/kernel/module/main.c
> index 08b59c37735e..322b38c0a782 100644
> --- a/kernel/module/main.c
> +++ b/kernel/module/main.c
> [...]
>  	pr_debug("Final section addresses for %s:\n", mod->name);
> @@ -2693,8 +2694,8 @@ static int move_module(struct module *mod, struct load_info *info)
>  	return 0;
>  out_err:
>  	module_memory_restore_rox(mod);
> -	for (t--; t >= 0; t--)
> -		module_memory_free(mod, t);
> +	for (; t > 0; t--)
> +		module_memory_free(mod, t - 1);
>  	if (codetag_section_found)
>  		codetag_free_module_sections(mod);
>  

This can actually be simply:

	while (t--)
		module_memory_free(mod, t);

-- Petr