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From:   Al Viro <viro@ZenIV.linux.org.uk>
To:     linux-fsdevel@vger.kernel.org
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        linux-kernel@vger.kernel.org, Aleksa Sarai <cyphar@cyphar.com>,
        David Howells <dhowells@redhat.com>,
        Eric Biederman <ebiederm@xmission.com>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        Al Viro <viro@zeniv.linux.org.uk>
Subject: [PATCH 16/17] LOOKUP_MOUNTPOINT: fold path_mountpointat() into path_lookupat()
Date:   Sun, 19 Jan 2020 03:17:28 +0000
Message-Id: <20200119031738.2681033-16-viro@ZenIV.linux.org.uk>
In-Reply-To: <20200119031738.2681033-1-viro@ZenIV.linux.org.uk>
References: <20200119031423.GV8904@ZenIV.linux.org.uk>
 <20200119031738.2681033-1-viro@ZenIV.linux.org.uk>
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From: Al Viro <viro@zeniv.linux.org.uk>

New LOOKUP flag, telling path_lookupat() to act as path_mountpointat().
IOW, traverse mounts at the final point and skip revalidation of the
location where it ends up.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
 fs/autofs/dev-ioctl.c |  6 +--
 fs/internal.h         |  1 -
 fs/namei.c            | 89 +++----------------------------------------
 fs/namespace.c        |  4 +-
 include/linux/namei.h |  2 +-
 5 files changed, 12 insertions(+), 90 deletions(-)

diff --git a/fs/autofs/dev-ioctl.c b/fs/autofs/dev-ioctl.c
index a3cdb0036c5d..f3a0f412b43b 100644
--- a/fs/autofs/dev-ioctl.c
+++ b/fs/autofs/dev-ioctl.c
@@ -186,7 +186,7 @@ static int find_autofs_mount(const char *pathname,
 	struct path path;
 	int err;
 
-	err = kern_path_mountpoint(AT_FDCWD, pathname, &path, 0);
+	err = kern_path(pathname, LOOKUP_MOUNTPOINT, &path);
 	if (err)
 		return err;
 	err = -ENOENT;
@@ -519,8 +519,8 @@ static int autofs_dev_ioctl_ismountpoint(struct file *fp,
 
 	if (!fp || param->ioctlfd == -1) {
 		if (autofs_type_any(type))
-			err = kern_path_mountpoint(AT_FDCWD,
-						   name, &path, LOOKUP_FOLLOW);
+			err = kern_path(name, LOOKUP_FOLLOW | LOOKUP_MOUNTPOINT,
+					&path);
 		else
 			err = find_autofs_mount(name, &path,
 						test_by_type, &type);
diff --git a/fs/internal.h b/fs/internal.h
index 4a7da1df573d..07695e0f56fe 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -61,7 +61,6 @@ extern int finish_clean_context(struct fs_context *fc);
  */
 extern int filename_lookup(int dfd, struct filename *name, unsigned flags,
 			   struct path *path, struct path *root);
-extern int user_path_mountpoint_at(int, const char __user *, unsigned int, struct path *);
 extern int vfs_path_lookup(struct dentry *, struct vfsmount *,
 			   const char *, unsigned int, struct path *);
 long do_mknodat(int dfd, const char __user *filename, umode_t mode,
diff --git a/fs/namei.c b/fs/namei.c
index 6c28b969f4d1..6852a0dcb25d 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2250,6 +2250,10 @@ static int path_lookupat(struct nameidata *nd, unsigned flags, struct path *path
 	if (!err && nd->flags & LOOKUP_DIRECTORY)
 		if (!d_can_lookup(nd->path.dentry))
 			err = -ENOTDIR;
+	if (!err && unlikely(nd->flags & LOOKUP_MOUNTPOINT)) {
+		err = handle_lookup_down(nd);
+		nd->flags &= ~LOOKUP_JUMPED; // no d_weak_revalidate(), please...
+	}
 	if (!err) {
 		*path = nd->path;
 		nd->path.mnt = NULL;
@@ -2278,7 +2282,8 @@ int filename_lookup(int dfd, struct filename *name, unsigned flags,
 		retval = path_lookupat(&nd, flags | LOOKUP_REVAL, path);
 
 	if (likely(!retval))
-		audit_inode(name, path->dentry, 0);
+		audit_inode(name, path->dentry,
+			    flags & LOOKUP_MOUNTPOINT ? AUDIT_INODE_NOEVAL : 0);
 	restore_nameidata();
 	putname(name);
 	return retval;
@@ -2556,88 +2561,6 @@ int user_path_at_empty(int dfd, const char __user *name, unsigned flags,
 }
 EXPORT_SYMBOL(user_path_at_empty);
 
-/**
- * path_mountpoint - look up a path to be umounted
- * @nd:		lookup context
- * @flags:	lookup flags
- * @path:	pointer to container for result
- *
- * Look up the given name, but don't attempt to revalidate the last component.
- * Returns 0 and "path" will be valid on success; Returns error otherwise.
- */
-static int
-path_mountpoint(struct nameidata *nd, unsigned flags, struct path *path)
-{
-	const char *s = path_init(nd, flags);
-	int err;
-
-	while (!(err = link_path_walk(s, nd)) &&
-		(err = lookup_last(nd)) > 0) {
-		s = trailing_symlink(nd);
-	}
-	if (!err && (nd->flags & LOOKUP_RCU))
-		err = unlazy_walk(nd);
-	if (!err)
-		err = handle_lookup_down(nd);
-	if (!err) {
-		*path = nd->path;
-		nd->path.mnt = NULL;
-		nd->path.dentry = NULL;
-	}
-	terminate_walk(nd);
-	return err;
-}
-
-static int
-filename_mountpoint(int dfd, struct filename *name, struct path *path,
-			unsigned int flags)
-{
-	struct nameidata nd;
-	int error;
-	if (IS_ERR(name))
-		return PTR_ERR(name);
-	set_nameidata(&nd, dfd, name);
-	error = path_mountpoint(&nd, flags | LOOKUP_RCU, path);
-	if (unlikely(error == -ECHILD))
-		error = path_mountpoint(&nd, flags, path);
-	if (unlikely(error == -ESTALE))
-		error = path_mountpoint(&nd, flags | LOOKUP_REVAL, path);
-	if (likely(!error))
-		audit_inode(name, path->dentry, AUDIT_INODE_NOEVAL);
-	restore_nameidata();
-	putname(name);
-	return error;
-}
-
-/**
- * user_path_mountpoint_at - lookup a path from userland in order to umount it
- * @dfd:	directory file descriptor
- * @name:	pathname from userland
- * @flags:	lookup flags
- * @path:	pointer to container to hold result
- *
- * A umount is a special case for path walking. We're not actually interested
- * in the inode in this situation, and ESTALE errors can be a problem. We
- * simply want track down the dentry and vfsmount attached at the mountpoint
- * and avoid revalidating the last component.
- *
- * Returns 0 and populates "path" on success.
- */
-int
-user_path_mountpoint_at(int dfd, const char __user *name, unsigned int flags,
-			struct path *path)
-{
-	return filename_mountpoint(dfd, getname(name), path, flags);
-}
-
-int
-kern_path_mountpoint(int dfd, const char *name, struct path *path,
-			unsigned int flags)
-{
-	return filename_mountpoint(dfd, getname_kernel(name), path, flags);
-}
-EXPORT_SYMBOL(kern_path_mountpoint);
-
 int __check_sticky(struct inode *dir, struct inode *inode)
 {
 	kuid_t fsuid = current_fsuid();
diff --git a/fs/namespace.c b/fs/namespace.c
index b37dc59bfa05..b31a75782a59 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1669,7 +1669,7 @@ int ksys_umount(char __user *name, int flags)
 	struct path path;
 	struct mount *mnt;
 	int retval;
-	int lookup_flags = 0;
+	int lookup_flags = LOOKUP_MOUNTPOINT;
 
 	if (flags & ~(MNT_FORCE | MNT_DETACH | MNT_EXPIRE | UMOUNT_NOFOLLOW))
 		return -EINVAL;
@@ -1680,7 +1680,7 @@ int ksys_umount(char __user *name, int flags)
 	if (!(flags & UMOUNT_NOFOLLOW))
 		lookup_flags |= LOOKUP_FOLLOW;
 
-	retval = user_path_mountpoint_at(AT_FDCWD, name, lookup_flags, &path);
+	retval = user_path_at(AT_FDCWD, name, lookup_flags, &path);
 	if (retval)
 		goto out;
 	mnt = real_mount(path.mnt);
diff --git a/include/linux/namei.h b/include/linux/namei.h
index 07bfb0874033..df3549de1cd1 100644
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -22,6 +22,7 @@ enum {LAST_NORM, LAST_ROOT, LAST_DOT, LAST_DOTDOT, LAST_BIND};
 #define LOOKUP_AUTOMOUNT	0x0004  /* force terminal automount */
 #define LOOKUP_EMPTY		0x4000	/* accept empty path [user_... only] */
 #define LOOKUP_DOWN		0x8000	/* follow mounts in the starting point */
+#define LOOKUP_MOUNTPOINT	0x0080	/* follow mounts in the end */
 
 #define LOOKUP_REVAL		0x0020	/* tell ->d_revalidate() to trust no cache */
 #define LOOKUP_RCU		0x0040	/* RCU pathwalk mode; semi-internal */
@@ -54,7 +55,6 @@ extern struct dentry *kern_path_create(int, const char *, struct path *, unsigne
 extern struct dentry *user_path_create(int, const char __user *, struct path *, unsigned int);
 extern void done_path_create(struct path *, struct dentry *);
 extern struct dentry *kern_path_locked(const char *, struct path *);
-extern int kern_path_mountpoint(int, const char *, struct path *, unsigned int);
 
 extern struct dentry *try_lookup_one_len(const char *, struct dentry *, int);
 extern struct dentry *lookup_one_len(const char *, struct dentry *, int);
-- 
2.20.1