Unverified Commit 193feb69 authored by Christian Brauner's avatar Christian Brauner
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Merge patch series 'Fix shmem_rename2 directory offset calculation' of... 

Merge patch series 'Fix shmem_rename2 directory offset calculation' of https://lore.kernel.org/r/20240415152057.4605-1-cel@kernel.org

Pull shmem_rename2() offset fixes from Chuck Lever:

The existing code in shmem_rename2() allocates a fresh directory
offset value when renaming over an existing destination entry. User
space does not expect this behavior. In particular, applications
that rename while walking a directory can loop indefinitely because
they never reach the end of the directory.

* 'Fix shmem_rename2 directory offset calculation' of https://lore.kernel.org/r/20240415152057.4605-1-cel@kernel.org

: (3 commits)
  shmem: Fix shmem_rename2()
  libfs: Add simple_offset_rename() API
  libfs: Fix simple_offset_rename_exchange()

 fs/libfs.c         | 55 +++++++++++++++++++++++++++++++++++++++++-----
 include/linux/fs.h |  2 ++
 mm/shmem.c         |  3 +--
 3 files changed, 52 insertions(+), 8 deletions(-)

Signed-off-by: default avatarChristian Brauner <brauner@kernel.org>
parents c6854e5a ad191eb6

fs/libfs.c

+49 −6
Original line number Diff line number Diff line
@@ -295,6 +295,18 @@ int simple_offset_add(struct offset_ctx *octx, struct dentry *dentry) 
	return 0;

}



static int simple_offset_replace(struct offset_ctx *octx, struct dentry *dentry,

				 long offset)

{

	int ret;



	ret = mtree_store(&octx->mt, offset, dentry, GFP_KERNEL);

	if (ret)

		return ret;

	offset_set(dentry, offset);

	return 0;

}



/**

 * simple_offset_remove - Remove an entry to a directory's offset map

 * @octx: directory offset ctx to be updated
@@ -345,6 +357,36 @@ int simple_offset_empty(struct dentry *dentry) 
	return ret;

}



/**

 * simple_offset_rename - handle directory offsets for rename

 * @old_dir: parent directory of source entry

 * @old_dentry: dentry of source entry

 * @new_dir: parent_directory of destination entry

 * @new_dentry: dentry of destination

 *

 * Caller provides appropriate serialization.

 *

 * User space expects the directory offset value of the replaced

 * (new) directory entry to be unchanged after a rename.

 *

 * Returns zero on success, a negative errno value on failure.

 */

int simple_offset_rename(struct inode *old_dir, struct dentry *old_dentry,

			 struct inode *new_dir, struct dentry *new_dentry)

{

	struct offset_ctx *old_ctx = old_dir->i_op->get_offset_ctx(old_dir);

	struct offset_ctx *new_ctx = new_dir->i_op->get_offset_ctx(new_dir);

	long new_offset = dentry2offset(new_dentry);



	simple_offset_remove(old_ctx, old_dentry);



	if (new_offset) {

		offset_set(new_dentry, 0);

		return simple_offset_replace(new_ctx, old_dentry, new_offset);

	}

	return simple_offset_add(new_ctx, old_dentry);

}



/**

 * simple_offset_rename_exchange - exchange rename with directory offsets

 * @old_dir: parent of dentry being moved
@@ -352,6 +394,9 @@ int simple_offset_empty(struct dentry *dentry) 
 * @new_dir: destination parent

 * @new_dentry: destination dentry

 *

 * This API preserves the directory offset values. Caller provides

 * appropriate serialization.

 *

 * Returns zero on success. Otherwise a negative errno is returned and the

 * rename is rolled back.

 */
@@ -369,11 +414,11 @@ int simple_offset_rename_exchange(struct inode *old_dir, 
	simple_offset_remove(old_ctx, old_dentry);

	simple_offset_remove(new_ctx, new_dentry);



	ret = simple_offset_add(new_ctx, old_dentry);

	ret = simple_offset_replace(new_ctx, old_dentry, new_index);

	if (ret)

		goto out_restore;



	ret = simple_offset_add(old_ctx, new_dentry);

	ret = simple_offset_replace(old_ctx, new_dentry, old_index);

	if (ret) {

		simple_offset_remove(new_ctx, old_dentry);

		goto out_restore;
@@ -388,10 +433,8 @@ int simple_offset_rename_exchange(struct inode *old_dir, 
	return 0;



out_restore:

	offset_set(old_dentry, old_index);

	mtree_store(&old_ctx->mt, old_index, old_dentry, GFP_KERNEL);

	offset_set(new_dentry, new_index);

	mtree_store(&new_ctx->mt, new_index, new_dentry, GFP_KERNEL);

	(void)simple_offset_replace(old_ctx, old_dentry, old_index);

	(void)simple_offset_replace(new_ctx, new_dentry, new_index);

	return ret;

}

include/linux/fs.h

+2 −0
Original line number Diff line number Diff line
@@ -3353,6 +3353,8 @@ void simple_offset_init(struct offset_ctx *octx); 
int simple_offset_add(struct offset_ctx *octx, struct dentry *dentry);

void simple_offset_remove(struct offset_ctx *octx, struct dentry *dentry);

int simple_offset_empty(struct dentry *dentry);

int simple_offset_rename(struct inode *old_dir, struct dentry *old_dentry,

			 struct inode *new_dir, struct dentry *new_dentry);

int simple_offset_rename_exchange(struct inode *old_dir,

				  struct dentry *old_dentry,

				  struct inode *new_dir,

mm/shmem.c

+1 −2
Original line number Diff line number Diff line
@@ -3473,8 +3473,7 @@ static int shmem_rename2(struct mnt_idmap *idmap, 
			return error;

	}



	simple_offset_remove(shmem_get_offset_ctx(old_dir), old_dentry);

	error = simple_offset_add(shmem_get_offset_ctx(new_dir), old_dentry);

	error = simple_offset_rename(old_dir, old_dentry, new_dir, new_dentry);

	if (error)

		return error;