linux-kernel - Re: [PATCH] comedi: Fix potential memory leak in comedi

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Date:   Tue, 1 Nov 2022 05:45:15 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Shang XiaoJing <shangxiaojing@...wei.com>
Cc:     abbotti@....co.uk, hsweeten@...ionengravers.com,
        zhangxuezhi1@...lpad.com, fmhess@...rs.sourceforge.net,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] comedi: Fix potential memory leak in comedi_init()

On Tue, Nov 01, 2022 at 11:21:25AM +0800, Shang XiaoJing wrote:
> comedi_init() will goto out_unregister_chrdev_region if cdev_add()
> failed, which won't free the resource alloced in kobject_set_name().
> Call kfree_const() to free the leaked name before goto
> out_unregister_chrdev_region.
> 
> unreferenced object 0xffff8881000fa8c0 (size 8):
>   comm "modprobe", pid 239, jiffies 4294905173 (age 51.308s)
>   hex dump (first 8 bytes):
>     63 6f 6d 65 64 69 00 ff                          comedi..
>   backtrace:
>     [<000000005f9878f7>] __kmalloc_node_track_caller+0x4c/0x1c0
>     [<000000000fd70302>] kstrdup+0x3f/0x70
>     [<000000009428bc33>] kstrdup_const+0x46/0x60
>     [<00000000ed50d9de>] kvasprintf_const+0xdb/0xf0
>     [<00000000b2766964>] kobject_set_name_vargs+0x3c/0xe0
>     [<00000000f2424ef7>] kobject_set_name+0x62/0x90
>     [<000000005d5a125b>] 0xffffffffa0013098
>     [<00000000f331e663>] do_one_initcall+0x7a/0x380
>     [<00000000aa7bac96>] do_init_module+0x5c/0x230
>     [<000000005fd72335>] load_module+0x227d/0x2420
>     [<00000000ad550cf1>] __do_sys_finit_module+0xd5/0x140
>     [<00000000069a60c5>] do_syscall_64+0x3f/0x90
>     [<00000000c5e0d521>] entry_SYSCALL_64_after_hwframe+0x63/0xcd
> 
> Fixes: ed9eccbe8970 ("Staging: add comedi core")
> Signed-off-by: Shang XiaoJing <shangxiaojing@...wei.com>
> ---
>  drivers/comedi/comedi_fops.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/comedi/comedi_fops.c b/drivers/comedi/comedi_fops.c
> index e2114bcf815a..2c508c2cf6f6 100644
> --- a/drivers/comedi/comedi_fops.c
> +++ b/drivers/comedi/comedi_fops.c
> @@ -3379,8 +3379,11 @@ static int __init comedi_init(void)
>  
>  	retval = cdev_add(&comedi_cdev, MKDEV(COMEDI_MAJOR, 0),
>  			  COMEDI_NUM_MINORS);
> -	if (retval)
> +	if (retval) {
> +		kfree_const(comedi_cdev.kobj.name);
> +		comedi_cdev.kobj.name = NULL;
>  		goto out_unregister_chrdev_region;
> +	}

A driver should never have to poke around in the internals of a cdev
object like this.  Please fix the cdev core to not need this if
cdev_add() fails.

thanks,

greg k-h