[PATCH v3 3/4] of/overlay: rewrite /aliases path values to live-tree paths

[Abdurrahman Hussain]

/aliases entries added by an overlay reference labeled nodes inside
the overlay via '&label' in the .dtso. dtc renders those references
as string paths at compile time, but the paths encode the overlay's
internal fragment layout (e.g. "/fragment@1/__overlay__/fpga@0/i2c@40000")
rather than the location where the node will live after apply.

Currently only /__symbols__ has its property values rewritten from
overlay-internal paths to live-tree paths by dup_and_fixup_symbol_prop().
/aliases values fall through the plain __of_prop_dup() path and are
copied byte-for-byte, so of_find_node_by_path() on such a value returns
NULL, of_alias_get_id() reports -ENODEV — and the reconfig notifier
added earlier in this series sees uninterpretable paths and can't
populate aliases_lookup for overlay-declared aliases.

The values in /aliases follow the same textual convention as
/__symbols__, so we can reuse the existing rewriter. Detect the
/aliases target node, reject values that aren't non-empty C strings
null-terminated within pp->length (of_alias_get_id() and
of_find_node_by_path() dereference alias values as C strings, so a
malformed one must not reach the live tree through either dup path),
and then route values with a "/fragment@" prefix through
dup_and_fixup_symbol_prop(). Other alias values — legacy string
aliases like "ttyS0" that some out-of-tree code writes verbatim —
pass through the plain __of_prop_dup() path unchanged.

Discriminating up-front instead of falling back to a raw dup when
dup_and_fixup_symbol_prop() returns NULL matters: a fallback would
inject the unrewritten fragment path into the live tree where nothing
can resolve it. With the string shape validated here, a NULL return
means either allocation failure or a fragment path that doesn't
resolve within the overlay; both are reported as -ENOMEM, matching
the existing /__symbols__ handling of the same helper. Distinguishing
the two would require an ERR_PTR conversion of the shared helper and
is left for a separate cleanup.

Signed-off-by: Abdurrahman Hussain <abdurrahman@xxxxxxxxxx>
---
 drivers/of/overlay.c | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
index b6545905cf67..9f85278c577a 100644
--- a/drivers/of/overlay.c
+++ b/drivers/of/overlay.c
@@ -350,6 +350,21 @@ static int add_changeset_property(struct overlay_changeset *ovcs,
 		if (prop)
 			return -EINVAL;
 		new_prop = dup_and_fixup_symbol_prop(ovcs, overlay_prop);
+	} else if (target->np->parent &&
+		   of_node_is_root(target->np->parent) &&
+		   of_node_name_eq(target->np, "aliases")) {
+		/* /aliases values are deref'd as C strings; reject malformed input */
+		if (!overlay_prop->value || overlay_prop->length < 2 ||
+		    strnlen(overlay_prop->value, overlay_prop->length) >=
+			overlay_prop->length)
+			return -EINVAL;
+
+		/* rewrite overlay-internal paths to live-tree paths */
+		if (!strncmp(overlay_prop->value, "/fragment@",
+			     strlen("/fragment@")))
+			new_prop = dup_and_fixup_symbol_prop(ovcs, overlay_prop);
+		else
+			new_prop = __of_prop_dup(overlay_prop, GFP_KERNEL);
 	} else {
 		new_prop = __of_prop_dup(overlay_prop, GFP_KERNEL);
 	}

-- 
2.54.0