Subject: Re: Recent Linus' tree, kernel BUG at fs/inode.c:1436!

From: Pavel Emelyanov <[email-masked]>
Date: Fri, 19 Dec 2014 15:08:42 +0300

On 12/19/2014 03:01 PM, Al Viro wrote:
> On Fri, Dec 19, 2014 at 02:34:00PM +0300, Pavel Emelyanov wrote:
>> Hi,
>>
>> It looks like there's a strange refcount underflow in VFS/socket code.
>> The proggie [1] crashes the recent Linus' tree (d790be38 Merge tag
>> 'modules-next-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/rusty/linux) 
>> with the calltrace [2].
>>
>> If in the proggie the psk is replaced with non-socket descriptor the
>> issue doesn't appear.
> 
> Gyah... mismerge on cherry-pick.  My fault - ->i_fop assignment should've
> been removed from sock_alloc_file() in bd9b51.  Could you verify that the
> following recovers the things?
> 
> diff --git a/net/socket.c b/net/socket.c
> index 70bbde6..a2c33a4 100644
> --- a/net/socket.c
> +++ b/net/socket.c
> @@ -372,7 +372,6 @@ struct file *sock_alloc_file(struct socket *sock, int flags, const char *dname)
>  	path.mnt = mntget(sock_mnt);
>  
>  	d_instantiate(path.dentry, SOCK_INODE(sock));
> -	SOCK_INODE(sock)->i_fop = &socket_file_ops;
>  
>  	file = alloc_file(&path, FMODE_READ | FMODE_WRITE,
>  		  &socket_file_ops);
> .
> 

Acked-by: Pavel Emelyanov <[email-masked]>

This also makes socket non-open-able back again, which, in turn, was
another issue I was surprised with on the new kernel :)

Thanks,
Pavel