[PATCH v6 06/10] of/overlay: only treat a positive changeset id as registered

of_overlay_fdt_apply() stores the idr_alloc() return value in
ovcs->id before checking it. On failure the stored id is negative,
free_overlay_changeset()'s "if (ovcs->id)" check passes, idr_remove()
is called with a negative id and list_del() runs on ovcs->ovcs_list,
which is not initialized until after the id allocation. An allocation
failure at that point dereferences NULL.

Make free_overlay_changeset() treat only a strict-positive id as
registered. The rest of the function already copes with a
partially-initialized ovcs, so the error path stays a plain
goto err_free_ovcs.

Fixes: 61b4de4e0b38 ("of: overlay: minor restructuring")
Cc: [email protected]
Suggested-by: Geert Uytterhoeven <[email protected]>
Assisted-by: Claude:claude-fable-5 [Claude Code]
Signed-off-by: Abdurrahman Hussain <[email protected]>
---
 drivers/of/overlay.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
index 284c9bc6c9cf..9b9f198a1d70 100644
--- a/drivers/of/overlay.c
+++ b/drivers/of/overlay.c
@@ -860,7 +860,8 @@ static void free_overlay_changeset(struct overlay_changeset *ovcs)
 	if (ovcs->cset.entries.next)
 		of_changeset_destroy(&ovcs->cset);
 
-	if (ovcs->id) {
+	/* a failed idr_alloc() leaves its negative error in ovcs->id */
+	if (ovcs->id > 0) {
 		idr_remove(&ovcs_idr, ovcs->id);
 		list_del(&ovcs->ovcs_list);
 		ovcs->id = 0;

-- 
2.54.0