netdev - Re: [PATCH v3] net-sysfs: Fix reference count leak

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Date:   Mon, 18 Nov 2019 14:27:05 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     jouni.hogander@...kie.com
Cc:     netdev@...r.kernel.org, David Miller <davem@...emloft.net>,
        Lukas Bulwahn <lukas.bulwahn@...il.com>
Subject: Re: [PATCH v3] net-sysfs: Fix reference count leak

On Mon, Nov 18, 2019 at 02:32:46PM +0200, jouni.hogander@...kie.com wrote:
> From: Jouni Hogander <jouni.hogander@...kie.com>
> 
> Netdev_register_kobject is calling device_initialize. In case of error
> reference taken by device_initialize is not given up.
> 
> Drivers are supposed to call free_netdev in case of error. In non-error
> case the last reference is given up there and device release sequence
> is triggered. In error case this reference is kept and the release
> sequence is never started.
> 
> Fix this reference count leak by allowing giving up the reference also
> in error case in free_netdev.
> 
> Also replace BUG_ON with WARN_ON in free_netdev and in netdev_release.
> 
> This is the rootcause for couple of memory leaks 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
> 
> BUG: memory leak
> unreferenced object 0xffff8880668ba588 (size 8):
>   comm "kobject_set_nam", pid 286, jiffies 4294725297 (age 9.871s)
>   hex dump (first 8 bytes):
>     6e 72 30 00 cc be df 2b                          nr0....+
>   backtrace:
>     [<00000000a322332a>] __kmalloc_track_caller+0x16e/0x290
>     [<00000000236fd26b>] kstrdup+0x3e/0x70
>     [<00000000dd4a2815>] kstrdup_const+0x3e/0x50
>     [<0000000049a377fc>] kvasprintf_const+0x10e/0x160
>     [<00000000627fc711>] kobject_set_name_vargs+0x5b/0x140
>     [<0000000019eeab06>] dev_set_name+0xc0/0xf0
>     [<0000000069cb12bc>] netdev_register_kobject+0xc8/0x320
>     [<00000000f2e83732>] register_netdevice+0xa1b/0xf00
>     [<000000009e1f57cc>] __tun_chr_ioctl+0x20d5/0x3dd0
>     [<000000009c560784>] tun_chr_ioctl+0x2f/0x40
>     [<000000000d759e02>] do_vfs_ioctl+0x1c7/0x1510
>     [<00000000351d7c31>] ksys_ioctl+0x99/0xb0
>     [<000000008390040a>] __x64_sys_ioctl+0x78/0xb0
>     [<0000000052d196b7>] do_syscall_64+0x16f/0x580
>     [<0000000019af9236>] entry_SYSCALL_64_after_hwframe+0x44/0xa9
>     [<00000000bc384531>] 0xffffffffffffffff
> 
> Reported-by: syzbot+ad8ca40ecd77896d51e2@...kaller.appspotmail.com
> Cc: David Miller <davem@...emloft.net>
> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> Cc: Lukas Bulwahn <lukas.bulwahn@...il.com>
> Signed-off-by: Jouni Hogander <jouni.hogander@...kie.com>
> ---
> v2 -> v3:
> * Replaced BUG_ON with WARN_ON in free_netdev and netdev_release
> v1 -> v2:
> * Relying on driver calling free_netdev rather than calling
>   put_device directly in error path
> ---
>  net/core/dev.c       | 14 +++++++-------
>  net/core/net-sysfs.c |  6 +++++-
>  2 files changed, 12 insertions(+), 8 deletions(-)
> 
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 99ac84ff398f..1d6c0bfb5ec5 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -9603,14 +9603,14 @@ void free_netdev(struct net_device *dev)
>  
>  	netdev_unregister_lockdep_key(dev);
>  
> -	/*  Compatibility with error handling in drivers */
> -	if (dev->reg_state == NETREG_UNINITIALIZED) {
> -		netdev_freemem(dev);
> -		return;
> -	}
> +	/* reg_state is NETREG_UNINITIALIZED if there is an error in
> +	 * registration.
> +	 */
> +	WARN_ON(dev->reg_state != NETREG_UNREGISTERED &&
> +		dev->reg_state != NETREG_UNINITIALIZED);

You "warn" about this, but do not actually handle the problem.  So what
is this helping with?

Systems with panic-on-warn just rebooted, and a "normal" system saw a
traceback yet no error handling happened so why would the code even test
this?

I'm not trying to be picky here, just to think about what you are doing
with these checks please.

thanks,

greg k-h