[Devel] [PATCH rh7] fs: drop useless d_root_check()

[Andrey Ryabinin]

d_root_check() takes the following locks in wrong order:

	write_seqlock(&rename_lock);
	br_read_lock(&vfsmount_lock);

thus we may endup with deadlock.
While we could fix it by taking these locks in reverse
order, it would be better to just delete this function.

d_root_check() is a leftover from pre-mount namespace days,
we don't need it today.

https://jira.sw.ru/browse/PSBM-41919

Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 fs/dcache.c            | 53 --------------------------------------------------
 fs/proc/base.c         | 31 +++++++++--------------------
 fs/proc/fd.c           |  2 +-
 include/linux/dcache.h |  1 -
 4 files changed, 10 insertions(+), 77 deletions(-)

diff --git a/fs/dcache.c b/fs/dcache.c
index a4f60d1..b5119e3 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -3220,59 +3220,6 @@ Elong:
 	return ERR_PTR(-ENAMETOOLONG);
 }
 
-/**
- * d_root_check - checks if dentry is accessible from current's fs root
- * @dentry: dentry to be verified
- * @vfsmnt: vfsmnt to which the dentry belongs
- */
-int d_root_check(struct path *path)
-{
-	struct dentry *dentry = path->dentry;
-	struct vfsmount *vfsmnt = path->mnt;
-	struct mount *mnt = real_mount(vfsmnt);
-	struct path root;
-	int error = 0;
-
-	if (ve_is_super(get_exec_env()))
-		return 0;
-
-	if (path->dentry->d_op && path->dentry->d_op->d_dname)
-		return 0;
-
-	/*
-	 * If we meet disconnected entry, it's allowed
-	 * to proceed, it comes from special allocations
-	 * such as opening by file handle, where dentry
-	 * formed directly from the inode opened.
-	 */
-	if (unlikely(dentry->d_flags & DCACHE_DISCONNECTED))
-		return 0;
-
-	get_fs_root(current->fs, &root);
-	write_seqlock(&rename_lock);
-	br_read_lock(&vfsmount_lock);
-	while (dentry != root.dentry || vfsmnt != root.mnt) {
-		if (dentry == vfsmnt->mnt_root || IS_ROOT(dentry)) {
-			/* Global root? */
-			if (!mnt_has_parent(mnt)) {
-				if (mnt->mnt_ns == ve0.ve_ns->mnt_ns)
-					error = -EACCES;
-				break;
-			}
-			dentry = mnt->mnt_mountpoint;
-			mnt = mnt->mnt_parent;
-			vfsmnt = &mnt->mnt;
-			continue;
-		}
-		dentry = dentry->d_parent;
-	}
-	br_read_unlock(&vfsmount_lock);
-	write_sequnlock(&rename_lock);
-	path_put(&root);
-
-	return error;
-}
-
 /*
  * NOTE! The user-level library version returns a
  * character pointer. The kernel system call just
diff --git a/fs/proc/base.c b/fs/proc/base.c
index b597b01..e9044e6 100644
--- a/fs/proc/base.c
+++ b/fs/proc/base.c
@@ -165,13 +165,9 @@ static int get_task_root(struct task_struct *task, struct path *root)
 	task_lock(task);
 	if (task->fs) {
 		get_fs_root(task->fs, root);
-		task_unlock(task);
-
-		result = d_root_check(root);
-		if (result)
-			path_put(root);
-	} else
-		task_unlock(task);
+		result = 0;
+	}
+	task_unlock(task);
 	return result;
 }
 
@@ -184,13 +180,9 @@ static int proc_cwd_link(struct dentry *dentry, struct path *path)
 		task_lock(task);
 		if (task->fs) {
 			get_fs_pwd(task->fs, path);
-			task_unlock(task);
-
-			result = d_root_check(path);
-			if (result)
-				path_put(path);
-		} else
-			task_unlock(task);
+			result = 0;
+		}
+		task_unlock(task);
 		put_task_struct(task);
 	}
 	return result;
@@ -1491,15 +1483,10 @@ static int proc_exe_link(struct dentry *dentry, struct path *exe_path)
 	exe_file = get_mm_exe_file(mm);
 	mmput(mm);
 	if (exe_file) {
-		int result;
-
-		result = d_root_check(&exe_file->f_path);
-		if (result == 0) {
-			*exe_path = exe_file->f_path;
-			path_get(&exe_file->f_path);
-		}
+		*exe_path = exe_file->f_path;
+		path_get(&exe_file->f_path);
 		fput(exe_file);
-		return result;
+		return 0;
 	} else
 		return -ENOENT;
 }
diff --git a/fs/proc/fd.c b/fs/proc/fd.c
index cf657f7..911dac9 100644
--- a/fs/proc/fd.c
+++ b/fs/proc/fd.c
@@ -158,7 +158,7 @@ static int proc_fd_link(struct dentry *dentry, struct path *path)
 		spin_lock(&files->file_lock);
 		fd_file = fcheck_files(files, fd);
 		ret = -EACCES;
-		if (fd_file && !d_root_check(&fd_file->f_path)) {
+		if (fd_file) {
 			*path = fd_file->f_path;
 			path_get(&fd_file->f_path);
 			ret = 0;
diff --git a/include/linux/dcache.h b/include/linux/dcache.h
index 56766a1..4a44f37 100644
--- a/include/linux/dcache.h
+++ b/include/linux/dcache.h
@@ -333,7 +333,6 @@ extern char *d_absolute_path(const struct path *, char *, int);
 extern char *d_path(const struct path *, char *, int);
 extern char *dentry_path_raw(struct dentry *, char *, int);
 extern char *dentry_path(struct dentry *, char *, int);
-extern int d_root_check(struct path *path);
 
 /* Allocation counts.. */
 
-- 
2.4.10