[RFC][PATCH v2 16/34] LOOKUP_MOUNTPOINT: fold path_mountpointat() into path_lookupat()

Al Viro
2020-02-23T01:20:45Z

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 f3f280b952a3..b108a8eb75ca 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 28835ee7168a..6f1f46b931a6 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -2382,6 +2382,10 @@ 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;
@@ -2410,7 +2414,8 @@ 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;
@@ -2688,88 +2693,6 @@ 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 a9e556224945..ef3f2a33992c 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 0dd980d7318f..d9576a051808 100644
--- a/include/linux/namei.h
+++ b/include/linux/namei.h
@@ -23,6 +23,7 @@ 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 */
@@ -64,7 +65,6 @@ 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);
--
2.11.0