From c2fd68b6b2b00f0a6280b5971028c10c8f0ba70f Mon Sep 17 00:00:00 2001 From: Christian Brauner Date: Tue, 27 Jul 2021 12:48:40 +0200 Subject: [PATCH] namei: add mapping aware lookup helper Various filesystems rely on the lookup_one_len() helper to lookup a single path component relative to a well-known starting point. Allow such filesystems to support idmapped mounts by adding a version of this helper to take the idmap into account when calling inode_permission(). This change is a required to let btrfs (and other filesystems) support idmapped mounts. Cc: Christoph Hellwig Cc: Al Viro Cc: Matthew Wilcox (Oracle) Cc: linux-fsdevel@vger.kernel.org Reviewed-by: Josef Bacik Reviewed-by: Christoph Hellwig Signed-off-by: Christian Brauner Signed-off-by: David Sterba --- fs/namei.c | 43 +++++++++++++++++++++++++++++++++++++------ include/linux/namei.h | 1 + 2 files changed, 38 insertions(+), 6 deletions(-) diff --git a/fs/namei.c b/fs/namei.c index bf6d8a738c59..902df46e7dd3 100644 --- a/fs/namei.c +++ b/fs/namei.c @@ -2575,8 +2575,9 @@ int vfs_path_lookup(struct dentry *dentry, struct vfsmount *mnt, } EXPORT_SYMBOL(vfs_path_lookup); -static int lookup_one_len_common(const char *name, struct dentry *base, - int len, struct qstr *this) +static int lookup_one_common(struct user_namespace *mnt_userns, + const char *name, struct dentry *base, int len, + struct qstr *this) { this->name = name; this->len = len; @@ -2604,7 +2605,7 @@ static int lookup_one_len_common(const char *name, struct dentry *base, return err; } - return inode_permission(&init_user_ns, base->d_inode, MAY_EXEC); + return inode_permission(mnt_userns, base->d_inode, MAY_EXEC); } /** @@ -2628,7 +2629,7 @@ struct dentry *try_lookup_one_len(const char *name, struct dentry *base, int len WARN_ON_ONCE(!inode_is_locked(base->d_inode)); - err = lookup_one_len_common(name, base, len, &this); + err = lookup_one_common(&init_user_ns, name, base, len, &this); if (err) return ERR_PTR(err); @@ -2655,7 +2656,7 @@ struct dentry *lookup_one_len(const char *name, struct dentry *base, int len) WARN_ON_ONCE(!inode_is_locked(base->d_inode)); - err = lookup_one_len_common(name, base, len, &this); + err = lookup_one_common(&init_user_ns, name, base, len, &this); if (err) return ERR_PTR(err); @@ -2664,6 +2665,36 @@ struct dentry *lookup_one_len(const char *name, struct dentry *base, int len) } EXPORT_SYMBOL(lookup_one_len); +/** + * lookup_one - filesystem helper to lookup single pathname component + * @mnt_userns: user namespace of the mount the lookup is performed from + * @name: pathname component to lookup + * @base: base directory to lookup from + * @len: maximum length @len should be interpreted to + * + * Note that this routine is purely a helper for filesystem usage and should + * not be called by generic code. + * + * The caller must hold base->i_mutex. + */ +struct dentry *lookup_one(struct user_namespace *mnt_userns, const char *name, + struct dentry *base, int len) +{ + struct dentry *dentry; + struct qstr this; + int err; + + WARN_ON_ONCE(!inode_is_locked(base->d_inode)); + + err = lookup_one_common(mnt_userns, name, base, len, &this); + if (err) + return ERR_PTR(err); + + dentry = lookup_dcache(&this, base, 0); + return dentry ? dentry : __lookup_slow(&this, base, 0); +} +EXPORT_SYMBOL(lookup_one); + /** * lookup_one_len_unlocked - filesystem helper to lookup single pathname component * @name: pathname component to lookup @@ -2683,7 +2714,7 @@ struct dentry *lookup_one_len_unlocked(const char *name, int err; struct dentry *ret; - err = lookup_one_len_common(name, base, len, &this); + err = lookup_one_common(&init_user_ns, name, base, len, &this); if (err) return ERR_PTR(err); diff --git a/include/linux/namei.h b/include/linux/namei.h index be9a2b349ca7..e89329bb3134 100644 --- a/include/linux/namei.h +++ b/include/linux/namei.h @@ -68,6 +68,7 @@ extern struct dentry *try_lookup_one_len(const char *, struct dentry *, int); extern struct dentry *lookup_one_len(const char *, struct dentry *, int); extern struct dentry *lookup_one_len_unlocked(const char *, struct dentry *, int); extern struct dentry *lookup_positive_unlocked(const char *, struct dentry *, int); +struct dentry *lookup_one(struct user_namespace *, const char *, struct dentry *, int); extern int follow_down_one(struct path *); extern int follow_down(struct path *);