[PATCH 17/34] namei: introduce struct renamedata

Christian Brauner
2020-10-29T00:36:21Z

In order to handle idmapped mounts we will extend the vfs rename helper
to take two new arguments in follow up patches. Since this operations already
takes a bunch of arguments add a simple struct renamedata (based on struct
nameidata) and make the current helper to use it before we extend it.

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
---
fs/namei.c | 144 ++++++++++++++++++++++++++++++++---------------------
1 file changed, 88 insertions(+), 56 deletions(-)

diff --git a/fs/namei.c b/fs/namei.c
index 76ee4d52bd5e..781f11795a22 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -4221,62 +4221,24 @@ SYSCALL_DEFINE2(link, const char __user *, oldname, const char __user *, newname
return do_linkat(AT_FDCWD, oldname, AT_FDCWD, newname, 0);
}

-/**
- * vfs_rename - rename a filesystem object
- * @old_dir: parent of source
- * @old_dentry: source
- * @new_dir: parent of destination
- * @new_dentry: destination
- * @delegated_inode: returns an inode needing a delegation break
- * @flags: rename flags
- *
- * The caller must hold multiple mutexes--see lock_rename()).
- *
- * If vfs_rename discovers a delegation in need of breaking at either
- * the source or destination, it will return -EWOULDBLOCK and return a
- * reference to the inode in delegated_inode. The caller should then
- * break the delegation and retry. Because breaking a delegation may
- * take a long time, the caller should drop all locks before doing
- * so.
- *
- * Alternatively, a caller may pass NULL for delegated_inode. This may
- * be appropriate for callers that expect the underlying filesystem not
- * to be NFS exported.
- *
- * The worst of all namespace operations - renaming directory. "Perverted"
- * doesn't even start to describe it. Somebody in UCB had a heck of a trip...
- * Problems:
- *
- * a) we can get into loop creation.
- * b) race potential - two innocent renames can create a loop together.
- * That's where 4.4 screws up. Current fix: serialization on
- * sb->s_vfs_rename_mutex. We might be more accurate, but that's another
- * story.
- * c) we have to lock _four_ objects - parents and victim (if it exists),
- * and source (if it is not a directory).
- * And that - after we got ->i_mutex on parents (until then we don't know
- * whether the target exists). Solution: try to be smart with locking
- * order for inodes. We rely on the fact that tree topology may change
- * only under ->s_vfs_rename_mutex _and_ that parent of the object we
- * move will be locked. Thus we can rank directories by the tree
- * (ancestors first) and rank all non-directories after them.
- * That works since everybody except rename does "lock parent, lookup,
- * lock child" and rename is under ->s_vfs_rename_mutex.
- * HOWEVER, it relies on the assumption that any object with ->lookup()
- * has no more than 1 dentry. If "hybrid" objects will ever appear,
- * we'd better make sure that there's no link(2) for them.
- * d) conversion from fhandle to dentry may come in the wrong moment - when
- * we are removing the target. Solution: we will have to grab ->i_mutex
- * in the fhandle_to_dentry code. [FIXME - current nfsfh.c relies on
- * ->i_mutex on parents, which works but leads to some truly excessive
- * locking].
- */
-int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
- struct inode *new_dir, struct dentry *new_dentry,
- struct inode **delegated_inode, unsigned int flags)
+struct renamedata {
+ struct inode *old_dir;
+ struct dentry *old_dentry;
+ struct inode *new_dir;
+ struct dentry *new_dentry;
+ struct inode **delegated_inode;
+ unsigned int flags;
+} __randomize_layout;
+
+static int __vfs_rename(struct renamedata *rd)
{
int error;
struct user_namespace *user_ns = &init_user_ns;
+ struct inode *old_dir = rd->old_dir, *new_dir = rd->new_dir;
+ struct dentry *old_dentry = rd->old_dentry,
+ *new_dentry = rd->new_dentry;
+ struct inode **delegated_inode = rd->delegated_inode;
+ unsigned int flags = rd->flags;
bool is_dir = d_is_dir(old_dentry);
struct inode *source = old_dentry->d_inode;
struct inode *target = new_dentry->d_inode;
@@ -4395,11 +4357,76 @@ int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,

return error;
}
+
+/**
+ * vfs_rename - rename a filesystem object
+ * @old_dir: parent of source
+ * @old_dentry: source
+ * @new_dir: parent of destination
+ * @new_dentry: destination
+ * @delegated_inode: returns an inode needing a delegation break
+ * @flags: rename flags
+ *
+ * The caller must hold multiple mutexes--see lock_rename()).
+ *
+ * If vfs_rename discovers a delegation in need of breaking at either
+ * the source or destination, it will return -EWOULDBLOCK and return a
+ * reference to the inode in delegated_inode. The caller should then
+ * break the delegation and retry. Because breaking a delegation may
+ * take a long time, the caller should drop all locks before doing
+ * so.
+ *
+ * Alternatively, a caller may pass NULL for delegated_inode. This may
+ * be appropriate for callers that expect the underlying filesystem not
+ * to be NFS exported.
+ *
+ * The worst of all namespace operations - renaming directory. "Perverted"
+ * doesn't even start to describe it. Somebody in UCB had a heck of a trip...
+ * Problems:
+ *
+ * a) we can get into loop creation.
+ * b) race potential - two innocent renames can create a loop together.
+ * That's where 4.4 screws up. Current fix: serialization on
+ * sb->s_vfs_rename_mutex. We might be more accurate, but that's another
+ * story.
+ * c) we have to lock _four_ objects - parents and victim (if it exists),
+ * and source (if it is not a directory).
+ * And that - after we got ->i_mutex on parents (until then we don't know
+ * whether the target exists). Solution: try to be smart with locking
+ * order for inodes. We rely on the fact that tree topology may change
+ * only under ->s_vfs_rename_mutex _and_ that parent of the object we
+ * move will be locked. Thus we can rank directories by the tree
+ * (ancestors first) and rank all non-directories after them.
+ * That works since everybody except rename does "lock parent, lookup,
+ * lock child" and rename is under ->s_vfs_rename_mutex.
+ * HOWEVER, it relies on the assumption that any object with ->lookup()
+ * has no more than 1 dentry. If "hybrid" objects will ever appear,
+ * we'd better make sure that there's no link(2) for them.
+ * d) conversion from fhandle to dentry may come in the wrong moment - when
+ * we are removing the target. Solution: we will have to grab ->i_mutex
+ * in the fhandle_to_dentry code. [FIXME - current nfsfh.c relies on
+ * ->i_mutex on parents, which works but leads to some truly excessive
+ * locking].
+ */
+int vfs_rename(struct inode *old_dir, struct dentry *old_dentry,
+ struct inode *new_dir, struct dentry *new_dentry,
+ struct inode **delegated_inode, unsigned int flags)
+{
+ struct renamedata rd = {
+ .old_dir = old_dir,
+ .new_dir = new_dir,
+ .old_dentry = old_dentry,
+ .delegated_inode = delegated_inode,
+ .flags = flags,
+ };
+ return __vfs_rename(&rd);
+}
EXPORT_SYMBOL(vfs_rename);

static int do_renameat2(int olddfd, const char __user *oldname, int newdfd,
const char __user *newname, unsigned int flags)
{
+ struct renamedata rd;
struct dentry *old_dentry, *new_dentry;
struct dentry *trap;
struct path old_path, new_path;
@@ -4505,9 +4532,14 @@ static int do_renameat2(int olddfd, const char __user *oldname, int newdfd,
&new_path, new_dentry, flags);
if (error)
goto exit5;
- error = vfs_rename(old_path.dentry->d_inode, old_dentry,
- new_path.dentry->d_inode, new_dentry,
- &delegated_inode, flags);
+
+ rd.old_dir = old_path.dentry->d_inode;
+ rd.old_dentry = old_dentry;
+ rd.new_dir = new_path.dentry->d_inode;
+ rd.new_dentry = new_dentry;
+ rd.delegated_inode = &delegated_inode;
+ rd.flags = flags;
+ error = __vfs_rename(&rd);
exit5:
dput(new_dentry);
exit4:
--
2.29.0