Revert "proc: fix races against execve() of /proc/PID/fd**"

This reverts commit aa6afca5.

It escalates of some of the google-chrome SELinux problems with ptrace
("Check failed: pid_ > 0.  Did not find zygote process"), and Andrew
says that it is also causing mystery lockdep reports.
Reported-by: NAlex Villacís Lasso <a_villacis@palosanto.com>
Requested-by: NJames Morris <jmorris@namei.org>
Requested-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

fs/proc/base.c

@@ -1652,46 +1652,12 @@ static int proc_pid_readlink(struct dentry * dentry, char __user * buffer, int b
 	return error;
 }
 
-static int proc_pid_fd_link_getattr(struct vfsmount *mnt, struct dentry *dentry,
-		struct kstat *stat)
-{
-	struct inode *inode = dentry->d_inode;
-	struct task_struct *task = get_proc_task(inode);
-	int rc;
-
-	if (task == NULL)
-		return -ESRCH;
-
-	rc = -EACCES;
-	if (lock_trace(task))
-		goto out_task;
-
-	generic_fillattr(inode, stat);
-	unlock_trace(task);
-	rc = 0;
-out_task:
-	put_task_struct(task);
-	return rc;
-}
-
 static const struct inode_operations proc_pid_link_inode_operations = {
 	.readlink	= proc_pid_readlink,
 	.follow_link	= proc_pid_follow_link,
 	.setattr	= proc_setattr,
 };
 
-static const struct inode_operations proc_fdinfo_link_inode_operations = {
-	.setattr	= proc_setattr,
-	.getattr	= proc_pid_fd_link_getattr,
-};
-
-static const struct inode_operations proc_fd_link_inode_operations = {
-	.readlink	= proc_pid_readlink,
-	.follow_link	= proc_pid_follow_link,
-	.setattr	= proc_setattr,
-	.getattr	= proc_pid_fd_link_getattr,
-};
-
 
 /* building an inode */
 
@@ -1923,61 +1889,49 @@ static unsigned name_to_int(struct dentry *dentry)
 
 static int proc_fd_info(struct inode *inode, struct path *path, char *info)
 {
-	struct task_struct *task;
-	struct files_struct *files;
+	struct task_struct *task = get_proc_task(inode);
+	struct files_struct *files = NULL;
 	struct file *file;
 	int fd = proc_fd(inode);
-	int rc;
-
-	task = get_proc_task(inode);
-	if (!task)
-		return -ENOENT;
-
-	rc = -EACCES;
-	if (lock_trace(task))
-		goto out_task;
-
-	rc = -ENOENT;
-	files = get_files_struct(task);
-	if (files == NULL)
-		goto out_unlock;
 
-	/*
-	 * We are not taking a ref to the file structure, so we must
-	 * hold ->file_lock.
-	 */
-	spin_lock(&files->file_lock);
-	file = fcheck_files(files, fd);
-	if (file) {
-		unsigned int f_flags;
-		struct fdtable *fdt;
-
-		fdt = files_fdtable(files);
-		f_flags = file->f_flags & ~O_CLOEXEC;
-		if (FD_ISSET(fd, fdt->close_on_exec))
-			f_flags |= O_CLOEXEC;
-
-		if (path) {
-			*path = file->f_path;
-			path_get(&file->f_path);
+	if (task) {
+		files = get_files_struct(task);
+		put_task_struct(task);
+	}
+	if (files) {
+		/*
+		 * We are not taking a ref to the file structure, so we must
+		 * hold ->file_lock.
+		 */
+		spin_lock(&files->file_lock);
+		file = fcheck_files(files, fd);
+		if (file) {
+			unsigned int f_flags;
+			struct fdtable *fdt;
+
+			fdt = files_fdtable(files);
+			f_flags = file->f_flags & ~O_CLOEXEC;
+			if (FD_ISSET(fd, fdt->close_on_exec))
+				f_flags |= O_CLOEXEC;
+
+			if (path) {
+				*path = file->f_path;
+				path_get(&file->f_path);
+			}
+			if (info)
+				snprintf(info, PROC_FDINFO_MAX,
+					 "pos:\t%lli\n"
+					 "flags:\t0%o\n",
+					 (long long) file->f_pos,
+					 f_flags);
+			spin_unlock(&files->file_lock);
+			put_files_struct(files);
+			return 0;
 		}
-		if (info)
-			snprintf(info, PROC_FDINFO_MAX,
-				 "pos:\t%lli\n"
-				 "flags:\t0%o\n",
-				 (long long) file->f_pos,
-				 f_flags);
-		rc = 0;
-	} else
-		rc = -ENOENT;
-	spin_unlock(&files->file_lock);
-	put_files_struct(files);
-
-out_unlock:
-	unlock_trace(task);
-out_task:
-	put_task_struct(task);
-	return rc;
+		spin_unlock(&files->file_lock);
+		put_files_struct(files);
+	}
+	return -ENOENT;
 }
 
 static int proc_fd_link(struct inode *inode, struct path *path)
@@ -2072,7 +2026,7 @@ static struct dentry *proc_fd_instantiate(struct inode *dir,
 	spin_unlock(&files->file_lock);
 	put_files_struct(files);
 
-	inode->i_op = &proc_fd_link_inode_operations;
+	inode->i_op = &proc_pid_link_inode_operations;
 	inode->i_size = 64;
 	ei->op.proc_get_link = proc_fd_link;
 	d_set_d_op(dentry, &tid_fd_dentry_operations);
@@ -2104,12 +2058,7 @@ static struct dentry *proc_lookupfd_common(struct inode *dir,
 	if (fd == ~0U)
 		goto out;
 
-	result = ERR_PTR(-EACCES);
-	if (lock_trace(task))
-		goto out;
-
 	result = instantiate(dir, dentry, task, &fd);
-	unlock_trace(task);
 out:
 	put_task_struct(task);
 out_no_task:
@@ -2129,28 +2078,23 @@ static int proc_readfd_common(struct file * filp, void * dirent,
 	retval = -ENOENT;
 	if (!p)
 		goto out_no_task;
-
-	retval = -EACCES;
-	if (lock_trace(p))
-		goto out;
-
 	retval = 0;
 
 	fd = filp->f_pos;
 	switch (fd) {
 		case 0:
 			if (filldir(dirent, ".", 1, 0, inode->i_ino, DT_DIR) < 0)
-				goto out_unlock;
+				goto out;
 			filp->f_pos++;
 		case 1:
 			ino = parent_ino(dentry);
 			if (filldir(dirent, "..", 2, 1, ino, DT_DIR) < 0)
-				goto out_unlock;
+				goto out;
 			filp->f_pos++;
 		default:
 			files = get_files_struct(p);
 			if (!files)
-				goto out_unlock;
+				goto out;
 			rcu_read_lock();
 			for (fd = filp->f_pos-2;
 			     fd < files_fdtable(files)->max_fds;
@@ -2174,9 +2118,6 @@ static int proc_readfd_common(struct file * filp, void * dirent,
 			rcu_read_unlock();
 			put_files_struct(files);
 	}
-
-out_unlock:
-	unlock_trace(p);
 out:
 	put_task_struct(p);
 out_no_task:
@@ -2254,7 +2195,6 @@ static struct dentry *proc_fdinfo_instantiate(struct inode *dir,
 	ei->fd = fd;
 	inode->i_mode = S_IFREG | S_IRUSR;
 	inode->i_fop = &proc_fdinfo_file_operations;
-	inode->i_op = &proc_fdinfo_link_inode_operations;
 	d_set_d_op(dentry, &tid_fd_dentry_operations);
 	d_add(dentry, inode);
 	/* Close the race of the process dying before we return the dentry */