Re: proc/bus.usb regression in : [NETNS]: Fix /proc/net breakage

[Giacomo Catenazzi <cate@cateee.net>]

Andrew Morton wrote:
> On Thu, 06 Dec 2007 09:21:53 +0100 Giacomo Catenazzi <cate@cateee.net> wrote:
> 
>> Andrew Morton wrote:
>>> On Mon, 3 Dec 2007 19:00:25 GMT Linux Kernel Mailing List <linux-kernel@vger.kernel.org> wrote:
>>>
>>>> Gitweb:     http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=2b1e300a9dfc3196ccddf6f1d74b91b7af55e416
>>>> Commit:     2b1e300a9dfc3196ccddf6f1d74b91b7af55e416
>>>> Parent:     e03ba84adb62fbc6049325a5bc00ef6932fa5e39
>>>> Author:     Eric W. Biederman <ebiederm@xmission.com>
>>>> AuthorDate: Sun Dec 2 00:33:17 2007 +1100
>>>> Committer:  Herbert Xu <herbert@gondor.apana.org.au>
>>>> CommitDate: Sun Dec 2 00:33:17 2007 +1100
>>>>
>>>>     [NETNS]: Fix /proc/net breakage
>>>>     
>>>>     Well I clearly goofed when I added the initial network namespace support
>>>>     for /proc/net.  Currently things work but there are odd details visible to
>>>>     user space, even when we have a single network namespace.
>>>>     
>>>>     Since we do not cache proc_dir_entry dentries at the moment we can just
>>>>     modify ->lookup to return a different directory inode depending on the
>>>>     network namespace of the process looking at /proc/net, replacing the
>>>>     current technique of using a magic and fragile follow_link method.
>>>>     
>>>>     To accomplish that this patch:
>>>>     - introduces a shadow_proc method to allow different dentries to
>>>>       be returned from proc_lookup.
>>>>     - Removes the old /proc/net follow_link magic
>>>>     - Fixes a weakness in our not caching of proc generic dentries.
>>>>     
>>>>     As shadow_proc uses a task struct to decided which dentry to return we can
>>>>     go back later and fix the proc generic caching without modifying any code
>>>>     that uses the shadow_proc method.
>>> This patch caused the binfmt_misc regression reported in
>>> http://bugzilla.kernel.org/show_bug.cgi?id=9504
>> This patch also doesn't allow to mount /proc/bus/usb
>>
> 
> Does Denis's patch fix it?

Yes, this patch solve the problem.
Tested-by: Giacomo Catenazzi <cate@debian.org>

ciao
	cate

> 
> Thanks.
> 
> 
> From: "Denis V. Lunev" <den@openvz.org>
> 
> /proc/sys/fs/binfmt_misc dentry disappeared during d_revalidate. 
> d_revalidate only dentries from shadowed one and below. 
> http://bugzilla.kernel.org/show_bug.cgi?id=9504
> 
> Cc: Eric W. Biederman <ebiederm@xmission.com>
> Cc: Marcus Better <marcus@better.se>
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> Cc: Marcus Better <marcus@better.se>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
> 
>  fs/proc/generic.c |   14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff -puN fs/proc/generic.c~lost-content-of-proc-sys-fs-binfmt_misc fs/proc/generic.c
> --- a/fs/proc/generic.c~lost-content-of-proc-sys-fs-binfmt_misc
> +++ a/fs/proc/generic.c
> @@ -380,12 +380,17 @@ static int proc_revalidate_dentry(struct
>  	return 0;
>  }
>  
> -static struct dentry_operations proc_dentry_operations =
> +static struct dentry_operations proc_dentry_shadow_operations =
>  {
>  	.d_delete	= proc_delete_dentry,
>  	.d_revalidate	= proc_revalidate_dentry,
>  };
>  
> +static struct dentry_operations proc_dentry_operations =
> +{
> +	.d_delete	= proc_delete_dentry,
> +};
> +
>  /*
>   * Don't create negative dentries here, return -ENOENT by hand
>   * instead.
> @@ -394,6 +399,7 @@ struct dentry *proc_lookup(struct inode 
>  {
>  	struct inode *inode = NULL;
>  	struct proc_dir_entry * de;
> +	int use_shadow = 0;
>  	int error = -ENOENT;
>  
>  	lock_kernel();
> @@ -406,8 +412,10 @@ struct dentry *proc_lookup(struct inode 
>  			if (!memcmp(dentry->d_name.name, de->name, de->namelen)) {
>  				unsigned int ino;
>  
> -				if (de->shadow_proc)
> +				if (de->shadow_proc) {
>  					de = de->shadow_proc(current, de);
> +					use_shadow = 1;
> +				}
>  				ino = de->low_ino;
>  				de_get(de);
>  				spin_unlock(&proc_subdir_lock);
> @@ -423,6 +431,8 @@ struct dentry *proc_lookup(struct inode 
>  
>  	if (inode) {
>  		dentry->d_op = &proc_dentry_operations;
> +		dentry->d_op = use_shadow ?
> +			&proc_dentry_shadow_operations : dentry->d_parent->d_op;
>  		d_add(dentry, inode);
>  		return NULL;
>  	}
> _
>