linux-kernel - Re: debugfs_create_u32

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Message-ID: <20200620074542.GA2298609@kroah.com>
Date:   Sat, 20 Jun 2020 09:45:42 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Ronald Tschalär <ronald@...ovation.ch>,
        Nicolai Stange <nicstange@...il.com>,
        David Rientjes <rientjes@...gle.com>,
        Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org
Subject: Re: debugfs_create_u32_array() memory leaks

On Fri, Jun 19, 2020 at 04:17:34PM -0700, Jakub Kicinski wrote:
> Hi!
> 
> I'm trying to use debugfs_create_u32_array() in drivers/net/netdevsim
> and it causes memory leaks:
> 
> unreferenced object 0xffff8880546642a0 (size 16):
>   comm "test_udp_tuns.s", pid 2146, jiffies 4294928368 (age 3772.435s)
>   hex dump (first 16 bytes):
>     84 52 6a 4d 80 88 ff ff 04 00 00 00 f3 78 7e 89  .RjM.........x~.
>   backtrace:
>     [<000000006962a447>] debugfs_create_u32_array+0x3f/0x90
> 
> I can see that debugfs_create_u32_array() allocates a structure at
> create time that ends up assigned to inode->i_private, but I don't 
> see it freed anywhere.
> 
> Am I missing something? I'm pretty sure files get removed, cause the
> driver calls debugfs_remove_recursive() and no other file types leaks.

Yeah, that's a bug, nice catch.  The debugfs_create*() functions should
not allocate local memory as we can't know to free that memory when the
file is removed.

Can you fix this up, or do you want me to?  I only see one in-kernel
user of this, so it shouldn't be that tough to do so.  The one user
never removes that file so that's why no one noticed this before.

thanks,

greg k-h