Re: [RFC][PATCH v2] procfs: Always expose /proc/<pid>/map_files/ and make it readable

["Kirill A. Shutemov" <kirill@shutemov.name>]

On Fri, Jan 23, 2015 at 07:15:44PM -0800, Calvin Owens wrote:
> Currently, /proc/<pid>/map_files/ is restricted to CAP_SYS_ADMIN, and
> is only exposed if CONFIG_CHECKPOINT_RESTORE is set. This interface
> is very useful for enumerating the files mapped into a process when
> the more verbose information in /proc/<pid>/maps is not needed.
> 
> This patch moves the folder out from behind CHECKPOINT_RESTORE, and
> removes the CAP_SYS_ADMIN restrictions. Following the links requires
> the ability to ptrace the process in question, so this doesn't allow
> an attacker to do anything they couldn't already do before.
> 
> Signed-off-by: Calvin Owens <calvinowens@fb.com>

Cc +linux-api@

> ---
> Changes in v2: 	Removed the follow_link() stub that returned -EPERM if
> 		the caller didn't have CAP_SYS_ADMIN, since the caller
> 		in my chroot() scenario gets -EACCES anyway.
> 
>  fs/proc/base.c | 18 ------------------
>  1 file changed, 18 deletions(-)
> 
> diff --git a/fs/proc/base.c b/fs/proc/base.c
> index 3f3d7ae..67b15ac 100644
> --- a/fs/proc/base.c
> +++ b/fs/proc/base.c
> @@ -1632,8 +1632,6 @@ end_instantiate:
>  	return dir_emit(ctx, name, len, 1, DT_UNKNOWN);
>  }
>  
> -#ifdef CONFIG_CHECKPOINT_RESTORE
> -
>  /*
>   * dname_to_vma_addr - maps a dentry name into two unsigned longs
>   * which represent vma start and end addresses.
> @@ -1660,11 +1658,6 @@ static int map_files_d_revalidate(struct dentry *dentry, unsigned int flags)
>  	if (flags & LOOKUP_RCU)
>  		return -ECHILD;
>  
> -	if (!capable(CAP_SYS_ADMIN)) {
> -		status = -EPERM;
> -		goto out_notask;
> -	}
> -
>  	inode = dentry->d_inode;
>  	task = get_proc_task(inode);
>  	if (!task)
> @@ -1792,10 +1785,6 @@ static struct dentry *proc_map_files_lookup(struct inode *dir,
>  	int result;
>  	struct mm_struct *mm;
>  
> -	result = -EPERM;
> -	if (!capable(CAP_SYS_ADMIN))
> -		goto out;
> -
>  	result = -ENOENT;
>  	task = get_proc_task(dir);
>  	if (!task)
> @@ -1849,10 +1838,6 @@ proc_map_files_readdir(struct file *file, struct dir_context *ctx)
>  	struct map_files_info *p;
>  	int ret;
>  
> -	ret = -EPERM;
> -	if (!capable(CAP_SYS_ADMIN))
> -		goto out;
> -
>  	ret = -ENOENT;
>  	task = get_proc_task(file_inode(file));
>  	if (!task)
> @@ -2040,7 +2025,6 @@ static const struct file_operations proc_timers_operations = {
>  	.llseek		= seq_lseek,
>  	.release	= seq_release_private,
>  };
> -#endif /* CONFIG_CHECKPOINT_RESTORE */
>  
>  static int proc_pident_instantiate(struct inode *dir,
>  	struct dentry *dentry, struct task_struct *task, const void *ptr)
> @@ -2537,9 +2521,7 @@ static const struct inode_operations proc_task_inode_operations;
>  static const struct pid_entry tgid_base_stuff[] = {
>  	DIR("task",       S_IRUGO|S_IXUGO, proc_task_inode_operations, proc_task_operations),
>  	DIR("fd",         S_IRUSR|S_IXUSR, proc_fd_inode_operations, proc_fd_operations),
> -#ifdef CONFIG_CHECKPOINT_RESTORE
>  	DIR("map_files",  S_IRUSR|S_IXUSR, proc_map_files_inode_operations, proc_map_files_operations),
> -#endif
>  	DIR("fdinfo",     S_IRUSR|S_IXUSR, proc_fdinfo_inode_operations, proc_fdinfo_operations),
>  	DIR("ns",	  S_IRUSR|S_IXUGO, proc_ns_dir_inode_operations, proc_ns_dir_operations),
>  #ifdef CONFIG_NET
> -- 
> 1.8.1
> 
> --
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-- 
 Kirill A. Shutemov