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namei: add mapping aware lookup helper

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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 <hch@infradead.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: linux-fsdevel@vger.kernel.org
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Christian Brauner 2021-07-27 12:48:40 +02:00 committed by David Sterba
parent e7849e33cf
commit c2fd68b6b2
2 changed files with 38 additions and 6 deletions
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43
fs/namei.c
View File

@ -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);

1
include/linux/namei.h
View File

@ -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 *);