[Devel] [RFC] Allow access to /proc/$PID/fd after setuid()

[Kirill Korotaev]

Acked-By: Kirill Korotaev <dev at openvz.org>

> /proc/$PID/fd has r-x------ permissions, so if process does setuid(), it
> will not be able to access /proc/*/fd/. This breaks fstatat() emulation
> in glibc.
> 
> open("foo", O_RDONLY|O_DIRECTORY)       = 4
> setuid32(65534)                         = 0
> stat64("/proc/self/fd/4/bar", 0xbfafb298) = -1 EACCES (Permission denied)
> 
> Signed-off-by: Alexey Dobriyan <adobriyan at openvz.org>
> ---
> 
>  fs/proc/base.c |   16 ++++++++++++++++
>  1 file changed, 16 insertions(+)
> 
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -1413,11 +1413,27 @@ static struct file_operations proc_fd_op
>  	.readdir	= proc_readfd,
>  };
>  
> +static int proc_fd_permission(struct inode *inode, int mask, struct nameidata *nd)
> +{
> +	struct task_struct *tsk;
> +	int rv;
> +
> +	rv = generic_permission(inode, mask, NULL);
> +	if (rv == 0)
> +		return 0;
> +	tsk = get_proc_task(inode);
> +	if (tsk == current)
> +		rv = 0;
> +	put_task_struct(tsk);
> +	return rv;
> +}
> +
>  /*
>   * proc directories can do almost nothing..
>   */
>  static struct inode_operations proc_fd_inode_operations = {
>  	.lookup		= proc_lookupfd,
> +	.permission	= proc_fd_permission,
>  	.setattr	= proc_setattr,
>  };
>  
> 
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