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

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Message-ID: <20250609221205.GA1439779@google.com>
Date: Mon, 9 Jun 2025 22:12:05 +0000
From: Sami Tolvanen <samitolvanen@...gle.com>
To: Petr Pavlu <petr.pavlu@...e.com>
Cc: Luis Chamberlain <mcgrof@...nel.org>,
	Daniel Gomez <da.gomez@...sung.com>, 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 Sun, Jun 08, 2025 at 09:25:34AM +0200, Petr Pavlu wrote:
> 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);

Looks correct to me either way.

Reviewed-by: Sami Tolvanen <samitolvanen@...gle.com>

Sami