From: Eric W. Biederman <ebiederm@xmission.com>

First we can access every /proc/<tgid>/task/<pid> directory as /proc/<pid> so
proc_task_permission is not usefully limiting visibility.

Second having related filesystems information should have nothing to do with
process visibility.  kill does not implement any checks like that.

Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
---

 fs/proc/base.c |   63 -----------------------------------------------
 1 files changed, 63 deletions(-)

diff -puN fs/proc/base.c~proc-remove-bogus-proc_task_permission fs/proc/base.c
--- devel/fs/proc/base.c~proc-remove-bogus-proc_task_permission	2006-04-14 23:42:17.000000000 -0700
+++ devel-akpm/fs/proc/base.c	2006-04-14 23:42:17.000000000 -0700
@@ -357,54 +357,6 @@ static int proc_root_link(struct inode *
 	return result;
 }
 
-
-/* Same as proc_root_link, but this addionally tries to get fs from other
- * threads in the group */
-static int proc_task_root_link(struct inode *inode, struct dentry **dentry,
-				struct vfsmount **mnt)
-{
-	struct fs_struct *fs;
-	int result = -ENOENT;
-	struct task_struct *leader = proc_task(inode);
-
-	task_lock(leader);
-	fs = leader->fs;
-	if (fs) {
-		atomic_inc(&fs->count);
-		task_unlock(leader);
-	} else {
-		/* Try to get fs from other threads */
-		task_unlock(leader);
-		read_lock(&tasklist_lock);
-		if (pid_alive(leader)) {
-			struct task_struct *task = leader;
-
-			while ((task = next_thread(task)) != leader) {
-				task_lock(task);
-				fs = task->fs;
-				if (fs) {
-					atomic_inc(&fs->count);
-					task_unlock(task);
-					break;
-				}
-				task_unlock(task);
-			}
-		}
-		read_unlock(&tasklist_lock);
-	}
-
-	if (fs) {
-		read_lock(&fs->lock);
-		*mnt = mntget(fs->rootmnt);
-		*dentry = dget(fs->root);
-		read_unlock(&fs->lock);
-		result = 0;
-		put_fs_struct(fs);
-	}
-	return result;
-}
-
-
 #define MAY_PTRACE(task) \
 	(task == current || \
 	(task->parent == current && \
@@ -596,20 +548,6 @@ static int proc_permission(struct inode 
 	return proc_check_root(inode);
 }
 
-static int proc_task_permission(struct inode *inode, int mask, struct nameidata *nd)
-{
-	struct dentry *root;
-	struct vfsmount *vfsmnt;
-
-	if (generic_permission(inode, mask, NULL) != 0)
-		return -EACCES;
-
-	if (proc_task_root_link(inode, &root, &vfsmnt))
-		return -ENOENT;
-
-	return proc_check_chroot(root, vfsmnt);
-}
-
 extern struct seq_operations proc_pid_maps_op;
 static int maps_open(struct inode *inode, struct file *file)
 {
@@ -1578,7 +1516,6 @@ static struct inode_operations proc_fd_i
 
 static struct inode_operations proc_task_inode_operations = {
 	.lookup		= proc_task_lookup,
-	.permission	= proc_task_permission,
 };
 
 #ifdef CONFIG_SECURITY
_