Patch "libfs: Fix simple_offset_rename_exchange()" has been added to the 6.8-stable tree

[Sasha Levin <sashal@xxxxxxxxxx>]

This is a note to let you know that I've just added the patch titled

    libfs: Fix simple_offset_rename_exchange()

to the 6.8-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     libfs-fix-simple_offset_rename_exchange.patch
and it can be found in the queue-6.8 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit 8fa66426898f17fc3eaad8929df6a62cff9b4088
Author: Chuck Lever <chuck.lever@xxxxxxxxxx>
Date:   Mon Apr 15 11:20:54 2024 -0400

    libfs: Fix simple_offset_rename_exchange()
    
    [ Upstream commit 23cdd0eed3f1fff3af323092b0b88945a7950d8e ]
    
    User space expects the replacement (old) directory entry to have
    the same directory offset after the rename.
    
    Suggested-by: Christian Brauner <brauner@xxxxxxxxxx>
    Fixes: a2e459555c5f ("shmem: stable directory offsets")
    Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
    Link: https://lore.kernel.org/r/20240415152057.4605-2-cel@xxxxxxxxxx
    Signed-off-by: Christian Brauner <brauner@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/fs/libfs.c b/fs/libfs.c
index d3d31197c8e43..c9516f3e14bb7 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -294,6 +294,18 @@ 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
@@ -351,6 +363,9 @@ 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.
  */
@@ -368,11 +383,11 @@ 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;
@@ -387,10 +402,8 @@ 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;
 }