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Date:   Fri, 15 Nov 2019 11:26:03 +0800
From:   Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To:     jouni.hogander@unikie.com
Cc:     linux-kernel@vger.kernel.org,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Lukas Bulwahn <lukas.bulwahn@gmail.com>
Subject: Re: [PATCH] drivers/base: Fix memory leak in error paths
Message-ID: <20191115032603.GG793701@kroah.com>
References: <20191114121840.5585-1-jouni.hogander@unikie.com>
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On Thu, Nov 14, 2019 at 02:18:40PM +0200, jouni.hogander@unikie.com wrote:
> From: Jouni Hogander <jouni.hogander@unikie.com>
> 
> Currently error paths are using device_del to clean-up preparations
> done by device_add. This is causing memory leak as free of dev->p
> allocated in device_add is freed in device_release. This is fixed by
> moving freeing dev->p to counterpart of device_add i.e. device_del.

Are you sure that is safe?  The device can still be "alive" after
device_del() is called.  The only place you know that it should be freed
is in the release callback.

> This memory leak was reported by Syzkaller:
> 
> BUG: memory leak unreferenced object 0xffff8880675ca008 (size 256):
>   comm "netdev_register", pid 281, jiffies 4294696663 (age 6.808s)
>   hex dump (first 32 bytes):
>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
>     00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
>   backtrace:
>     [<0000000058ca4711>] kmem_cache_alloc_trace+0x167/0x280
>     [<000000002340019b>] device_add+0x882/0x1750
>     [<000000001d588c3a>] netdev_register_kobject+0x128/0x380
>     [<0000000011ef5535>] register_netdevice+0xa1b/0xf00
>     [<000000007fcf1c99>] __tun_chr_ioctl+0x20d5/0x3dd0
>     [<000000006a5b7b2b>] tun_chr_ioctl+0x2f/0x40
>     [<00000000f30f834a>] do_vfs_ioctl+0x1c7/0x1510
>     [<00000000fba062ea>] ksys_ioctl+0x99/0xb0
>     [<00000000b1c1b8d2>] __x64_sys_ioctl+0x78/0xb0
>     [<00000000984cabb9>] do_syscall_64+0x16f/0x580
>     [<000000000bde033d>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
>     [<00000000e6ca2d9f>] 0xffffffffffffffff

How is this a leak?  This is in device_add(), not removing the device.
When the structure really is freed then it can be removed.

Or are you triggering an error in device_add() somehow to trigger this
callback?

thanks,

greg k-h