[PATCH v5 0/9] of: teach overlay code to keep /aliases in sync

[PATCH v5 0/9] of: teach overlay code to keep /aliases in sync

[Abdurrahman Hussain]

/aliases entries added by a device-tree overlay are stored in the live
tree but never enter the global aliases_lookup list that of_alias_scan()
builds at boot. As a result, of_alias_get_id() returns -ENODEV for
aliases declared inside overlays, and any driver that relies on
alias-based numbering (i2c-xiic, spi, tty, mmc, ...) silently loses its
pinned id and falls back to auto-assignment.

The gap has been public since 2015 [1] and reproduces trivially: apply
an overlay that declares e.g. `i2c99 = &foo;`, ask
of_alias_get_id(foo, "i2c") -> -ENODEV. Bootlin's ELCE 2025 talk on
PCI DT overlays [2] enumerates "i2c muxes" as one of the subsystems
broken by dynamic overlays; alias pinning is the underlying cause.

The core fix (patch 2) is a reconfig notifier that mirrors /aliases
property changes into aliases_lookup. Patch 1 prepares the alias path
lookup for /aliases becoming dynamic. Patches 3, 7 and 8 are the
overlay-code changes the use case needs; patches 4-6 fix pre-existing
bugs on paths the series exercises. Patch 9 adds a unittest.

Prior art
---------

Geert Uytterhoeven posted a 3-patch RFC in June 2015 [1] with the same
alias-tracking design shape. Grant Likely reviewed positively; merge
was gated on missing unittests and an object-lifetime concern the
author self-flagged, and the series was never reposted as non-RFC. Ten
years later, drivers/of/overlay.c still contains zero references to
aliases, of_alias_scan, or aliases_lookup.

Series contents
---------------

Patch 1 makes of_find_node_opts_by_path() hold a reference on
of_aliases across the alias walk (the walk itself stays lock-free;
devtree_lock covers only the pointer load, pairing with patch 2's
detach path) and validates alias values before dereferencing them.

Patch 2 adds a reconfig notifier that mirrors /aliases property
changes into aliases_lookup. It also refactors of_alias_scan()'s
per-property body into a helper of_alias_create() shared by the
boot-time scan and the runtime notifier. A one-bit `owned` flag on
struct alias_prop distinguishes kmalloc'd (overlay-time) entries
(kstrdup'd alias name, of_node_get'd target) from memblock-backed
(boot-time) ones so the remove path can't kfree the wrong storage.
The notifier keys off structural properties of the target node
(name + root-parent) rather than the of_aliases global, so overlays
that create /aliases from scratch on a system without a boot-time
aliases node are covered too. All aliases_lookup readers and writers
serialize on a dedicated aliases_mutex.

Patch 3 fixes find_target() so an overlay applied with a non-NULL
target base can still reach the DT root via target-path="/foo". The
current code unconditionally concatenates base + target-path via
"%pOF%s", so target-path="/aliases" resolves to "<base>/aliases" and
target-path="/" produces "<base>/" (never a valid node). After this
patch, an empty target-path continues to mean "the target base
itself" — preserving the shape used by drivers/misc/lan966x_pci.c,
the only in-tree caller of of_overlay_fdt_apply() that passes a
non-NULL base — while any non-empty target-path is looked up
absolutely.

Patch 4 fixes a pre-existing double-free in add_changeset_property():
a property freed on the of_changeset_add_property() error path stayed
linked in the target node's deadprops list and was freed again at
node release.

Patch 5 fixes a pre-existing NULL dereference in
of_overlay_fdt_apply()'s idr_alloc() error path (negative id stored,
list_del() on an uninitialized list head).

Patch 6 fixes pre-existing "//" result paths from
dup_and_fixup_symbol_prop() when a fragment targets the root node.

Patch 7 converts dup_and_fixup_symbol_prop() to return ERR_PTR so
callers can tell malformed values, not-overlay-internal paths, and
allocation failures apart — /__symbols__ errors stop being reported
as -ENOMEM regardless of cause — and makes it verify the value
actually descends through the matched fragment's __overlay__ node
before slicing, instead of cutting at an assumed prefix length.

Patch 8 rewrites /aliases property values from the overlay's internal
fragment path ("/<fragment>/__overlay__/...") to the live-tree path
that the node will occupy after apply. The overlay code already does
this for /__symbols__ via dup_and_fixup_symbol_prop(); /aliases uses
the same textual convention and can reuse the same helper. Without
this, patch 2's notifier receives paths that never resolve in the
live tree, so of_alias_get_id() still returns -ENODEV. Values that
don't resolve inside the overlay (legacy string aliases, malformed
junk) are copied verbatim and stay inert — consumers validate before
dereferencing — so no overlay that applied before this series stops
applying.

Patch 9 adds a unittest — overlay_alias.dtso plus
of_unittest_overlay_alias() — that applies an overlay with a
non-NULL target_base, declaring a labeled node under the base and an
`testcase-alias99 = &that-label` entry in DT-root /aliases, then
asserts of_alias_get_id() on the grafted node returns 99 after the
apply and of_alias_get_highest_id() reports the stem gone after the
revert. Missing any one of the three functional patches (notifier /
absolute-target-paths / alias path rewrite) causes the assertion to
fail.

Changes in v5
-------------

Numbering note: the 7-patch series posted on 2026-07-22 went out
mislabeled as a second v4 (a tooling mistake on my side). This
posting supersedes both v4 threads.

Addresses Krzysztof's review of the first v4 posting and the
automated review of the second:

Patch 1 (Krzysztof):
  - The property walk is lock-free again; devtree_lock covers only
    the of_aliases pointer load and of_node_get(). Removed properties
    stay on deadprops with ->next intact, so the node reference is
    what a walker needs — the loop never needed the lock. Retitled
    accordingly.
  - The commit message no longer refers to overlay-writable /aliases
    in the present tense at a point in the series where it isn't.

All patches (Krzysztof):
  - Commit messages rewritten and shortened.

New patch 5:
  - Fix a pre-existing NULL dereference in of_overlay_fdt_apply():
    a failed idr_alloc() left a negative id in ovcs->id, so
    free_overlay_changeset() ran idr_remove() with a negative id and
    list_del() on an uninitialized list head.

New patch 6:
  - Fix pre-existing "//" paths from dup_and_fixup_symbol_prop()
    when a fragment targets the root node; the malformed path made
    symbols (and now aliases) in such fragments unresolvable.

Link to the mislabeled second v4: https://patch.msgid.link/20260722-nh-of-alias-overlay-v4-0-fc96a40d2761@nexthop.ai

Changes in the second v4 posting (2026-07-22, 7 patches)
--------------------------------------------------------

Addresses the automated review of the first v4 posting (its patches
2, 3, and 6 drew no findings).

Patch 1:
  - of_alias_value_ok() additionally requires the value to be an
    absolute path (per the DT spec). A relative value naming another
    alias — including itself — sent of_find_node_by_path() into
    unbounded mutual recursion with alias resolution and exhausted
    the kernel stack; the shared helper closes it for the path
    lookup and of_alias_create() alike.

New patch 4:
  - Fix the pre-existing double-free in add_changeset_property():
    a property freed on the of_changeset_add_property() error path
    stayed linked in the target node's deadprops list and was freed
    again by of_node_release(). The property now goes onto deadprops
    only after the changeset entry is recorded, so the error path
    frees an unreferenced property. Flagged on every revision of
    this series; fixing it beats re-deferring it.

Patch 5 (was patch 4):
  - dup_and_fixup_symbol_prop() now verifies the value textually
    descends through the matched fragment's __overlay__ node before
    slicing. Previously only the first path component was resolved,
    so an absolute live-tree alias sharing its first component with
    a hand-named fragment (or a bogus /__symbols__ value) was sliced
    mid-string and rewritten to garbage. Prefix mismatch and
    too-short values are -ENODEV (not overlay-internal), no longer
    -EINVAL.

Link to v4: https://patch.msgid.link/20260721-nh-of-alias-overlay-v4-0-8ad097e31e36@nexthop.ai

Changes in v4
-------------

Addresses the automated review of v3, plus findings from a local
adversarial review pass over the v4 candidate.

New patch 1:
  - of_find_node_opts_by_path() walked of_aliases' property list with
    no lock and no node reference. Racy against devtree_lock-protected
    property surgery since the walk was introduced, but only reachable
    in practice once overlays can create and destroy /aliases.
    Prerequisite for the DETACH change below.
  - The reader also validates the value's shape (of_alias_value_ok())
    before dereferencing it as a C string — raw of_add_property()
    producers are not validated anywhere — and no longer passes the
    NULL value of an empty alias property to of_find_node_by_path().

Patch 2 (was patch 1):
  - DETACH_NODE now drops the reference taken at ATTACH_NODE after
    clearing the of_aliases pointer under devtree_lock. v3 kept the
    reference to protect lockless readers, but a kept reference
    violates the changeset-destroy contract —
    __of_changeset_entry_destroy() expects refcount 1 — so every
    apply/revert cycle of an /aliases-creating overlay logged
    "ERROR: memory leak" and permanently leaked the node. With the
    reader from patch 1 taking its own reference under devtree_lock,
    the put is safe.
  - The aliases_lookup sweep now runs only when the detached node is
    the tracked of_aliases, so a stray duplicate root node named
    "aliases" can no longer wipe entries backed by the real node; the
    node match is an exact-name compare (of_node_is_aliases()) since
    of_node_name_eq() would also match "aliases@1".
  - The notifier machinery is compiled only for CONFIG_OF_DYNAMIC;
    the of_reconfig_notifier_register() stub returns -EINVAL, so the
    unconditional core_initcall_sync failed on every non-dynamic DT
    kernel.
  - Per-entry teardown factored into __of_alias_del(); shared
    of_node_is_aliases()/of_alias_value_ok() helpers in of_private.h
    replace open-coded copies in base.c and overlay.c.

New patch 4:
  - dup_and_fixup_symbol_prop() returns ERR_PTR, distinguishing
    malformed values (-EINVAL), not-overlay-internal paths (-ENODEV),
    and allocation failure (-ENOMEM) — the discrimination v3's
    "/fragment@" prefix heuristic approximated, and the reason a
    structural failure was previously misreported as -ENOMEM.

Patch 5 (was patch 3):
  - Drop the "/fragment@" prefix heuristic: init_overlay_changeset()
    accepts fragments with any node name, so a hand-named fragment's
    alias would silently stay unrewritten (the bug this series fixes),
    and a live-tree path starting with "/fragment@" would fail apply.
    Discrimination now comes from where the value actually resolves
    (patch 4).
  - Malformed alias values no longer fail the overlay apply with
    -EINVAL; they are admitted verbatim with a warning and stay inert
    (consumers validate before dereferencing). An overlay that applied
    cleanly before this series keeps applying.
  - Exempt pseudo-properties from the /aliases handling: the
    is_pseudo_property() skip at the top of add_changeset_property()
    is gated on target->in_livetree, so a phandle (a raw cell, not a
    C string) of a newly created /aliases node could fail the string
    checks and abort a valid overlay.

Patch 6 (was patch 4):
  - Drop the grafted-node reference before of_overlay_remove();
    holding it across the revert trips the same changeset-destroy
    refcount check (kernel ERROR + leaked node).
  - Assert alias removal via of_alias_get_highest_id() — keyed by
    stem, needs no node reference — with a matching precondition
    check before the apply.
  - Wrap the apply in EXPECT_BEGIN/END for the standard "memory leak
    will occur" warning printed for properties added to a node the
    overlay didn't create.

Patch 3:
  - Document the empty-vs-absolute target-path contract in the
    kernel-doc for @base/@target_base and find_target(); the old text
    predated the semantic change.

Link to v3: https://patch.msgid.link/20260721-nh-of-alias-overlay-v3-0-7001028fe2f5@nexthop.ai

Changes in v3
-------------

Addresses the automated review of v2.

Patch 1:
  - of_device_uevent() in drivers/of/device.c now walks aliases_lookup
    under aliases_mutex; the previous of_mutex path could race with
    the reconfig notifier that mutates under aliases_mutex.
  - Drop the defensive ATTACH_NODE property scan. Overlay attach
    queues each property as a separate ADD_PROPERTY changeset entry,
    so per-property notifications cover the case that matters;
    walking rd->dn->properties without devtree_lock could race with
    concurrent DT mutations. A direct of_attach_node() caller that
    pre-populates /aliases loses tracking for those entries, matching
    pre-series behavior.
  - Replace DETACH_NODE's per-property forget with a single scan of
    aliases_lookup itself (same rationale). Boot-time entries are
    unlinked; memblock-backed struct + alias name are not freed.
  - of_alias_destroy() now of_node_puts() the target for every
    matching entry, closing a leak of the reference
    of_find_node_by_path() took at of_alias_scan() time for boot-time
    entries.

Patch 3:
  - Enforce non-empty + null-terminated-within-pp->length up-front
    for every /aliases property value. Values that don't match
    "/fragment@" now flow through __of_prop_dup() only after that
    validation, closing a pre-existing hole where a malformed alias
    value could reach the live tree.

Patch 4:
  - Hold a reference on the grafted target node across the revert
    so the post-remove assertion queries the right np, not the
    base. of_alias_get_id(base, ...) would trivially return -ENODEV
    regardless of whether removal actually cleaned up the alias.
  - On of_overlay_fdt_apply() failure, reclaim the (possibly
    partially-populated) ovcs_id via of_overlay_remove() to avoid
    leaking the unflattened FDT and partially-applied nodes.

Additional fixes from local review of the v3 candidate:

All patches:
  - Trim inline comments to the constraint being enforced; rationale
    and use-case narrative moved to the commit messages.

Patch 1:
  - of_alias_create() releases the target-node reference on every
    error path, not only for owned entries — restoring the original
    of_alias_scan() error behavior for boot-time entries.
  - Correct the struct alias_prop @owned kernel-doc: every entry holds
    a reference on @np (removal drops it regardless of @owned); the
    flag only selects whether the struct and alias name are kfree()d.
  - Correct the notifier-registration comment and commit message:
    of_alias_scan() runs pre-initcall from unflatten_device_tree() /
    of_pdt_build_devicetree(), not from of_core_init().
  - DETACH_NODE clears the of_aliases pointer but keeps the reference
    taken at ATTACH_NODE: of_find_node_opts_by_path() reads of_aliases
    and walks its properties locklessly, so the node must outlive any
    concurrent reader.
  - Call out (in the commit message) the pre-existing one-byte OOB
    read in the stem parser that the refactor fixes: isdigit() was
    tested before the end > start bound.

Patch 3:
  - Correct the commit-message claim that a NULL return from
    dup_and_fixup_symbol_prop() can only mean -ENOMEM; unresolvable
    fragment paths also return NULL and are reported as -ENOMEM,
    matching the existing /__symbols__ handling.

Patch 4:
  - Fix the .dtso label: dtc labels cannot contain hyphens, so
    testcase-target failed to compile. Now testcase_target.
  - Do not add overlay_alias.dtbo to the fdtoverlay static build
    test: fdtoverlay cannot resolve the empty (base-relative)
    target-path, so static_test_1.dtb would fail to build.
  - Drop the unnecessary #address-cells/#size-cells from the grafted
    node (dtc W=1 avoid_unnecessary_addr_size).

Changes in v2
-------------

Addressed the automated review of the RFC posting.

Patch 1:
  - Guard rd->old_prop before dereferencing in the UPDATE_PROPERTY
    handler; some notifier producers pass NULL.
  - Handle OF_RECONFIG_ATTACH_NODE and OF_RECONFIG_DETACH_NODE for
    /aliases nodes attached or detached with pre-populated properties.
    (v3 pared this back — see above.)
  - Serialize aliases_lookup with a dedicated aliases_mutex; readers
    (of_alias_get_id, of_alias_get_highest_id) and the reconfig
    notifier both hold it. Boot-time of_alias_scan() stays lockless
    (single-threaded during init).
  - Destroy path unlinks matching entries irrespective of ownership
    (freeing storage only for owned ones), so an overlay UPDATE
    against a boot-time alias no longer leaves duplicate stem+id
    entries in aliases_lookup.
  - Owned entries kstrdup the alias name and hold an of_node_get()
    reference on the target — released in the destroy path — so a
    property freed by overlay revert can't dangle into aliases_lookup.
  - of_aliases is refcounted lazily on ATTACH/DETACH.
  - Validate pp->value is non-empty and null-terminated within
    pp->length before feeding it to of_find_node_by_path() — prevents
    a stray malformed alias entry from causing an OOB read.

Patch 3:
  - Only route /aliases properties through dup_and_fixup_symbol_prop()
    when the value looks like a fragment-internal path. Other alias
    values pass through the raw duplicator unchanged. This removes
    the previous unconditional fallback that would silently propagate
    a raw dup on ENOMEM.

Patch 4:
  - Rewrite the .dtso to actually exercise all three functional
    patches: a labeled node under a fragment with target-path="" plus
    an /aliases fragment with target-path="/aliases" (absolute) and
    a value referencing the label via `&`. The RFC test bypassed
    patches 2 and 3.
  - Rewrite the runner to call of_overlay_fdt_apply() directly with a
    non-NULL target_base and assert against the grafted node's np.

Link to v1: https://patch.msgid.link/20260720-nh-of-alias-overlay-v1-0-27da6848dd84@nexthop.ai

Open items
----------

None outstanding. Pre-existing issues surfaced by the automated review
are unrelated to this series and are being tracked separately:
  - fragment target/overlay refcount leak on init_overlay_changeset()
    error paths (ovcs->count still 0 when free_overlay_changeset()
    runs),
  - node duplicated by __of_node_dup() leaked in add_changeset_node()
    when of_changeset_attach_node() fails,
  - of_node_put() under devtree_lock (raw spinlock) reaching
    fwnode_links_purge(),
  - lan966x_pci_probe() not reclaiming a populated ovcs_id when
    of_overlay_fdt_apply() fails.

Verification
------------

The OF unittest was run under QEMU (x86_64, OF_UNITTEST=y, v7.2-rc3
plus this series): of_unittest_overlay_alias() passes and the full
run reports 415 passed, 0 failed, with no unexpected "OF: ERROR:"
lines or changeset-destroy refcount complaints in the log. base.c
also builds with CONFIG_OF=y and CONFIG_OF_DYNAMIC=n (the notifier
machinery compiles out).

The series was also backported onto a 7.1-based image and boot-tested
on an x86 Nexthop switch with two PCI-attached Xilinx FPGAs whose
i2c-xiic controllers come from driver-embedded DT overlays applied
with a non-NULL target base. Before this series, i2c bus numbers
auto-assigned regardless of what /aliases said and shifted across
boots depending on which FPGA won the probe race. After: 95 i2c
adapters with /dev/i2c-N numbering matching the overlay aliases
exactly and stable across reboots, sensors reading live telemetry
through mux channels, and dmesg free of WARN/BUG/Oops and unexpected
OF errors. Runtime overlay revert via driver unbind was exercised on
the same hardware: the changeset revert removed all 153 of the
overlay's /aliases entries through the reconfig notifier with no
refcount or of_node_put errors, leaving the other overlay's 12
entries intact. (The revert then hangs in device teardown, in a
pre-existing i2c-xiic i2c_del_adapter() issue unrelated to this
series; the complete apply/revert cycle is covered by the unittest
under QEMU.)

[1] https://lore.kernel.org/lkml/1435675876-2159-1-git-send-email-geert+renesas@glider.be/
    Geert Uytterhoeven, "[PATCH/RFC 0/3] of/overlay: Update aliases
    when added or removed", 2015-06-30.
[2] Hervé Codina, "Using Device Tree Overlays to Support Complex PCI
    Devices in Linux", ELCE 2025.
    https://bootlin.com/pub/conferences/2025/elce/codina-pcie-dt-overlay.pdf

Assisted-by: Claude:claude-fable-5 [Claude Code]
Signed-off-by: Abdurrahman Hussain <abdurrahman@nexthop.ai>
---
Abdurrahman Hussain (9):
      of: hold a reference on of_aliases during alias path resolution
      of: update /aliases lookup on reconfig notifications
      of/overlay: look up absolute target-paths absolutely
      of/overlay: put property on deadprops only after changeset add succeeds
      of/overlay: don't keep a negative id in ovcs->id on idr_alloc() failure
      of/overlay: don't create "//" paths for fragments targeting the root
      of/overlay: return ERR_PTR from dup_and_fixup_symbol_prop()
      of/overlay: rewrite /aliases path values to live-tree paths
      of: unittest: cover /aliases updates from overlay apply/revert

 drivers/of/base.c                           | 230 ++++++++++++++++++++++------
 drivers/of/device.c                         |   4 +-
 drivers/of/of_private.h                     |  22 +++
 drivers/of/overlay.c                        |  98 ++++++++----
 drivers/of/unittest-data/Makefile           |   5 +
 drivers/of/unittest-data/overlay_alias.dtso |  25 +++
 drivers/of/unittest.c                       |  73 +++++++++
 7 files changed, 378 insertions(+), 79 deletions(-)
---
base-commit: a13c140cc289c0b7b3770bce5b3ad42ab35074aa
change-id: 20260719-nh-of-alias-overlay-6e5e0d56212b

Best regards,
--  
Abdurrahman Hussain <abdurrahman@nexthop.ai>

[PATCH v5 1/9] of: hold a reference on of_aliases during alias path resolution

[Abdurrahman Hussain]

of_find_node_opts_by_path() walks the property list of of_aliases
without taking a reference on the node and passes pp->value straight
to of_find_node_by_path().

Take a reference across the walk. The walk itself stays lock-free
like every other property iteration: removed properties keep their
->next and are only freed when the node is released, so the node
reference is sufficient. devtree_lock covers only the pointer load,
pairing it with a later patch in this series that clears of_aliases
and drops its reference when the node is detached at runtime.

Validate the value before resolving it. of_alias_value_ok() requires
a non-empty, NUL-terminated, absolute path:

  - an empty property has a NULL value and crashes in strchr()
  - a value without a NUL inside the property is read past its end
  - a relative value naming another alias (loop = "loop") recurses
    through of_find_node_by_path() until the stack is exhausted

All three are reachable with a malformed boot FDT today.

The name comparison loses its redundant strlen() pass while here.

Assisted-by: Claude:claude-fable-5 [Claude Code]
Signed-off-by: Abdurrahman Hussain <abdurrahman@nexthop.ai>
---
 drivers/of/base.c       | 20 +++++++++++++++-----
 drivers/of/of_private.h |  8 ++++++++
 2 files changed, 23 insertions(+), 5 deletions(-)

diff --git a/drivers/of/base.c b/drivers/of/base.c
index 6e7a42dedad3..6f79f593fc77 100644
--- a/drivers/of/base.c
+++ b/drivers/of/base.c
@@ -995,6 +995,8 @@ struct device_node *of_find_node_opts_by_path(const char *path, const char **opt
 
 	/* The path could begin with an alias */
 	if (*path != '/') {
+		struct device_node *aliases;
+		const char *value = NULL;
 		int len;
 		const char *p = strchrnul(path, '/');
 
@@ -1002,16 +1004,24 @@ struct device_node *of_find_node_opts_by_path(const char *path, const char **opt
 			p = separator;
 		len = p - path;
 
-		/* of_aliases must not be NULL */
-		if (!of_aliases)
+		/* the load pairs with writers that retire the node */
+		raw_spin_lock_irqsave(&devtree_lock, flags);
+		aliases = of_node_get(of_aliases);
+		raw_spin_unlock_irqrestore(&devtree_lock, flags);
+		if (!aliases)
 			return NULL;
 
-		for_each_property_of_node(of_aliases, pp) {
-			if (strlen(pp->name) == len && !strncmp(pp->name, path, len)) {
-				np = of_find_node_by_path(pp->value);
+		for_each_property_of_node(aliases, pp) {
+			if (!strncmp(pp->name, path, len) && !pp->name[len]) {
+				if (of_alias_value_ok(pp))
+					value = pp->value;
 				break;
 			}
 		}
+		/* the reference on @aliases keeps @value alive */
+		if (value)
+			np = of_find_node_by_path(value);
+		of_node_put(aliases);
 		if (!np)
 			return NULL;
 		path = p;
diff --git a/drivers/of/of_private.h b/drivers/of/of_private.h
index 0ae16da066e2..9bba999f0bf8 100644
--- a/drivers/of/of_private.h
+++ b/drivers/of/of_private.h
@@ -215,6 +215,14 @@ static inline bool is_pseudo_property(const char *prop_name)
 		!of_prop_cmp(prop_name, "linux,phandle");
 }
 
+/* alias values must be absolute paths NUL-terminated within length */
+static inline bool of_alias_value_ok(const struct property *pp)
+{
+	return pp->value && pp->length >= 2 &&
+	       *(const char *)pp->value == '/' &&
+	       strnlen(pp->value, pp->length) < pp->length;
+}
+
 #if IS_ENABLED(CONFIG_KUNIT)
 int __of_address_resource_bounds(struct resource *r, u64 start, u64 size);
 #endif

-- 
2.54.0

[PATCH v5 2/9] of: update /aliases lookup on reconfig notifications

[Abdurrahman Hussain]

Aliases added by overlays never make it into aliases_lookup, which is
only filled by of_alias_scan() at boot. of_alias_get_id() returns
-ENODEV for them and drivers using alias based numbering (i2c, spi,
tty, mmc) fall back to dynamic ids.

Register a reconfig notifier and mirror /aliases property changes
into aliases_lookup. The notifier chain covers changesets and
overlays, so no overlay specific hook is needed. Same approach as
Geert's 2015 series [1], which was never reposted;
of_alias_create()/of_alias_destroy() keep its names.

The /aliases node is matched by name and root parent instead of the
of_aliases pointer, which is still NULL when an overlay creates the
node on a system without a boot-time /aliases. The name match is
exact, of_node_name_eq() would also match "aliases@1". ATTACH stores
the node in of_aliases with a reference held, DETACH drops it again
and flushes aliases_lookup; the pointer updates happen under
devtree_lock to pair with the reader in of_find_node_opts_by_path().
Nodes attached with properties already set are not scanned, as
before.

Lookup entries are created by of_alias_scan()'s old loop body, moved
into of_alias_create(). Entries created at runtime have kstrdup'ed
names and an of_node_get'ed target and are flagged "owned" so
of_alias_destroy() knows what to kfree(); boot entries live in
memblock and are only unlinked. Removal matches entries regardless of
ownership so updating a boot-time alias does not leave duplicates
behind, which was Grant's main concern on the old series [2].

A new aliases_mutex protects the list. of_mutex does not work here:
the notifier runs under it on the overlay path but outside of it on
the of_add_property() path.

The rework also fixes an out-of-bounds read in the old stem parser,
which tested isdigit(*(end - 1)) before checking end > start and so
read one byte before the property name when the name was empty or all
digits. Such names are skipped now instead of getting an empty stem.

Only built for CONFIG_OF_DYNAMIC: there are no notifications without
it and the register stub returns -EINVAL.

Link: https://lore.kernel.org/lkml/1435675876-2159-1-git-send-email-geert+renesas@glider.be/ [1]
Link: https://lore.kernel.org/lkml/20150630172131.D4E6CC4041A@trevor.secretlab.ca/ [2]
Assisted-by: Claude:claude-fable-5 [Claude Code]
Signed-off-by: Abdurrahman Hussain <abdurrahman@nexthop.ai>
---
 drivers/of/base.c       | 210 +++++++++++++++++++++++++++++++++++++++---------
 drivers/of/device.c     |   4 +-
 drivers/of/of_private.h |  14 ++++
 3 files changed, 186 insertions(+), 42 deletions(-)

diff --git a/drivers/of/base.c b/drivers/of/base.c
index 6f79f593fc77..612e2cd31688 100644
--- a/drivers/of/base.c
+++ b/drivers/of/base.c
@@ -1925,6 +1925,170 @@ static void of_alias_add(struct alias_prop *ap, struct device_node *np,
 		 ap->alias, ap->stem, ap->id, np);
 }
 
+/*
+ * Protects aliases_lookup and of_aliases. of_alias_scan() runs single-
+ * threaded at init and skips it; every other reader/writer must hold it.
+ */
+DEFINE_MUTEX(aliases_mutex);
+
+/* Callers other than of_alias_scan() must hold @aliases_mutex. */
+static void of_alias_create(const struct property *pp,
+			    void *(*dt_alloc)(u64 size, u64 align),
+			    bool owned)
+{
+	const char *start = pp->name;
+	const char *end;
+	struct device_node *np;
+	struct alias_prop *ap;
+	const char *dup;
+	int id, len;
+
+	if (is_pseudo_property(pp->name))
+		return;
+
+	if (!of_alias_value_ok(pp))
+		return;
+
+	np = of_find_node_by_path(pp->value);
+	if (!np)
+		return;
+
+	end = start + strlen(start);
+	while (end > start && isdigit(*(end - 1)))
+		end--;
+	len = end - start;
+	if (len == 0)
+		goto out_put;
+
+	if (kstrtoint(end, 10, &id) < 0)
+		goto out_put;
+
+	ap = dt_alloc(sizeof(*ap) + len + 1, __alignof__(*ap));
+	if (!ap)
+		goto out_put;
+	memset(ap, 0, sizeof(*ap) + len + 1);
+
+	if (owned) {
+		dup = kstrdup(pp->name, GFP_KERNEL);
+		if (!dup) {
+			kfree(ap);
+			goto out_put;
+		}
+	} else {
+		dup = start;
+	}
+	ap->alias = dup;
+	ap->owned = owned;
+	of_alias_add(ap, np, id, start, len);
+	return;
+
+out_put:
+	of_node_put(np);
+}
+
+#ifdef CONFIG_OF_DYNAMIC
+/* Unlink @ap; free its storage if it was runtime-allocated. */
+static void __of_alias_del(struct alias_prop *ap)
+{
+	list_del(&ap->link);
+	of_node_put(ap->np);
+	if (ap->owned) {
+		kfree(ap->alias);
+		kfree(ap);
+	}
+}
+
+/* Callers must hold @aliases_mutex. */
+static void of_alias_destroy(const char *name)
+{
+	struct alias_prop *ap, *tmp;
+
+	list_for_each_entry_safe(ap, tmp, &aliases_lookup, link) {
+		if (strcmp(ap->alias, name) != 0)
+			continue;
+		__of_alias_del(ap);
+		return;
+	}
+}
+
+static void *alias_alloc(u64 size, u64 align)
+{
+	return kzalloc(size, GFP_KERNEL);
+}
+
+/* Callers must hold @aliases_mutex. */
+static void of_aliases_forget_all(void)
+{
+	struct alias_prop *ap, *tmp;
+
+	list_for_each_entry_safe(ap, tmp, &aliases_lookup, link)
+		__of_alias_del(ap);
+}
+
+static int of_aliases_reconfig_notifier(struct notifier_block *nb,
+					unsigned long action, void *arg)
+{
+	struct of_reconfig_data *rd = arg;
+	struct device_node *put = NULL;
+	unsigned long flags;
+
+	/* of_aliases may still be NULL when an overlay creates the node */
+	if (!rd->dn || !of_node_is_aliases(rd->dn))
+		return NOTIFY_DONE;
+
+	mutex_lock(&aliases_mutex);
+	switch (action) {
+	case OF_RECONFIG_ATTACH_NODE:
+		/* of_aliases is read under devtree_lock by alias path lookup */
+		raw_spin_lock_irqsave(&devtree_lock, flags);
+		if (!of_aliases)
+			of_aliases = of_node_get(rd->dn);
+		raw_spin_unlock_irqrestore(&devtree_lock, flags);
+		break;
+	case OF_RECONFIG_DETACH_NODE:
+		raw_spin_lock_irqsave(&devtree_lock, flags);
+		if (of_aliases == rd->dn) {
+			of_aliases = NULL;
+			put = rd->dn;
+		}
+		raw_spin_unlock_irqrestore(&devtree_lock, flags);
+		if (put) {
+			of_aliases_forget_all();
+			/* may free the node, so must sit outside devtree_lock */
+			of_node_put(put);
+		}
+		break;
+	case OF_RECONFIG_ADD_PROPERTY:
+		of_alias_create(rd->prop, alias_alloc, true);
+		break;
+	case OF_RECONFIG_REMOVE_PROPERTY:
+		of_alias_destroy(rd->prop->name);
+		break;
+	case OF_RECONFIG_UPDATE_PROPERTY:
+		if (rd->old_prop)
+			of_alias_destroy(rd->old_prop->name);
+		of_alias_create(rd->prop, alias_alloc, true);
+		break;
+	default:
+		break;
+	}
+	mutex_unlock(&aliases_mutex);
+	return NOTIFY_OK;
+}
+
+static struct notifier_block of_aliases_nb = {
+	.notifier_call = of_aliases_reconfig_notifier,
+};
+
+static int __init of_aliases_reconfig_init(void)
+{
+	return of_reconfig_notifier_register(&of_aliases_nb);
+}
+
+/* of_alias_scan() runs pre-initcall, so the boot-time scan is complete */
+core_initcall_sync(of_aliases_reconfig_init);
+#endif /* CONFIG_OF_DYNAMIC */
+
 /**
  * of_alias_scan - Scan all properties of the 'aliases' node
  * @dt_alloc:	An allocator that provides a virtual address to memory
@@ -1960,42 +2124,8 @@ void of_alias_scan(void * (*dt_alloc)(u64 size, u64 align))
 	if (!of_aliases)
 		return;
 
-	for_each_property_of_node(of_aliases, pp) {
-		const char *start = pp->name;
-		const char *end = start + strlen(start);
-		struct device_node *np;
-		struct alias_prop *ap;
-		int id, len;
-
-		/* Skip those we do not want to proceed */
-		if (is_pseudo_property(pp->name))
-			continue;
-
-		np = of_find_node_by_path(pp->value);
-		if (!np)
-			continue;
-
-		/* walk the alias backwards to extract the id and work out
-		 * the 'stem' string */
-		while (isdigit(*(end-1)) && end > start)
-			end--;
-		len = end - start;
-
-		if (kstrtoint(end, 10, &id) < 0) {
-			of_node_put(np);
-			continue;
-		}
-
-		/* Allocate an alias_prop with enough space for the stem */
-		ap = dt_alloc(sizeof(*ap) + len + 1, __alignof__(*ap));
-		if (!ap) {
-			of_node_put(np);
-			continue;
-		}
-		memset(ap, 0, sizeof(*ap) + len + 1);
-		ap->alias = start;
-		of_alias_add(ap, np, id, start, len);
-	}
+	for_each_property_of_node(of_aliases, pp)
+		of_alias_create(pp, dt_alloc, false);
 }
 
 /**
@@ -2013,7 +2143,7 @@ int of_alias_get_id(const struct device_node *np, const char *stem)
 	struct alias_prop *app;
 	int id = -ENODEV;
 
-	mutex_lock(&of_mutex);
+	mutex_lock(&aliases_mutex);
 	list_for_each_entry(app, &aliases_lookup, link) {
 		if (strcmp(app->stem, stem) != 0)
 			continue;
@@ -2023,7 +2153,7 @@ int of_alias_get_id(const struct device_node *np, const char *stem)
 			break;
 		}
 	}
-	mutex_unlock(&of_mutex);
+	mutex_unlock(&aliases_mutex);
 
 	return id;
 }
@@ -2041,7 +2171,7 @@ int of_alias_get_highest_id(const char *stem)
 	struct alias_prop *app;
 	int id = -ENODEV;
 
-	mutex_lock(&of_mutex);
+	mutex_lock(&aliases_mutex);
 	list_for_each_entry(app, &aliases_lookup, link) {
 		if (strcmp(app->stem, stem) != 0)
 			continue;
@@ -2049,7 +2179,7 @@ int of_alias_get_highest_id(const char *stem)
 		if (app->id > id)
 			id = app->id;
 	}
-	mutex_unlock(&of_mutex);
+	mutex_unlock(&aliases_mutex);
 
 	return id;
 }
diff --git a/drivers/of/device.c b/drivers/of/device.c
index b3dc78f2fa3a..fa0cc8129ab0 100644
--- a/drivers/of/device.c
+++ b/drivers/of/device.c
@@ -237,7 +237,7 @@ void of_device_uevent(const struct device *dev, struct kobj_uevent_env *env)
 	add_uevent_var(env, "OF_COMPATIBLE_N=%d", seen);
 
 	seen = 0;
-	mutex_lock(&of_mutex);
+	mutex_lock(&aliases_mutex);
 	list_for_each_entry(app, &aliases_lookup, link) {
 		if (dev->of_node == app->np) {
 			add_uevent_var(env, "OF_ALIAS_%d=%s", seen,
@@ -245,7 +245,7 @@ void of_device_uevent(const struct device *dev, struct kobj_uevent_env *env)
 			seen++;
 		}
 	}
-	mutex_unlock(&of_mutex);
+	mutex_unlock(&aliases_mutex);
 }
 EXPORT_SYMBOL_GPL(of_device_uevent);
 
diff --git a/drivers/of/of_private.h b/drivers/of/of_private.h
index 9bba999f0bf8..731b606ae3e3 100644
--- a/drivers/of/of_private.h
+++ b/drivers/of/of_private.h
@@ -17,6 +17,11 @@
  * @alias:	Alias property name
  * @np:		Pointer to device_node that the alias stands for
  * @id:		Index value from end of alias name
+ * @owned:	True for runtime entries, where the struct and @alias are
+ *		kmalloc'd/kstrdup'd and freed on removal. False for boot-time
+ *		entries, which live in memblock (@alias points into the FDT)
+ *		and are only unlinked. Every entry holds a reference on @np;
+ *		removal drops it regardless of @owned.
  * @stem:	Alias string without the index
  *
  * The structure represents one alias property of 'aliases' node as
@@ -27,6 +32,7 @@ struct alias_prop {
 	const char *alias;
 	struct device_node *np;
 	int id;
+	bool owned;
 	char stem[];
 };
 
@@ -40,6 +46,7 @@ struct alias_prop {
 
 extern struct mutex of_mutex;
 extern raw_spinlock_t devtree_lock;
+extern struct mutex aliases_mutex;
 extern struct list_head aliases_lookup;
 extern struct kset *of_kset;
 
@@ -223,6 +230,13 @@ static inline bool of_alias_value_ok(const struct property *pp)
 	       strnlen(pp->value, pp->length) < pp->length;
 }
 
+/* the /aliases node: root child with the exact name "aliases" */
+static inline bool of_node_is_aliases(const struct device_node *np)
+{
+	return of_node_is_root(np->parent) &&
+	       !strcmp(kbasename(np->full_name), "aliases");
+}
+
 #if IS_ENABLED(CONFIG_KUNIT)
 int __of_address_resource_bounds(struct resource *r, u64 start, u64 size);
 #endif

-- 
2.54.0

[PATCH v5 3/9] of/overlay: look up absolute target-paths absolutely

[Abdurrahman Hussain]

find_target() with a non-NULL target base concatenates the base path
and the fragment's target-path via "%pOF%s": target-path="/foo"
resolves to "<base>/foo" and can never reach the DT root. An overlay
applied with a base cannot both extend the base subtree and add
/aliases entries, which is what a PCI device declaring its
peripherals under dev_of_node() needs for alias-based bus numbering.

Treat any non-empty target-path as absolute. An empty target-path
still means the base itself, the only form used by the one in-tree
caller passing a base (drivers/misc/lan966x_pci.c).

Spell the contract out in the kernel-doc for @base/@target_base and
in find_target()'s strategy comment.

Assisted-by: Claude:claude-fable-5 [Claude Code]
Signed-off-by: Abdurrahman Hussain <abdurrahman@nexthop.ai>
---
 drivers/of/overlay.c | 38 ++++++++++++++++++--------------------
 1 file changed, 18 insertions(+), 20 deletions(-)

diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
index 08d5351746be..74aea704835a 100644
--- a/drivers/of/overlay.c
+++ b/drivers/of/overlay.c
@@ -688,12 +688,15 @@ static int build_changeset(struct overlay_changeset *ovcs)
  *
  * 1) "target" property containing the phandle of the target
  * 2) "target-path" property containing the path of the target
+ *
+ * With a non-NULL @target_base, an empty "target-path" means
+ * @target_base itself; any non-empty "target-path" is resolved
+ * absolutely from the live-tree root.
  */
 static struct device_node *find_target(const struct device_node *info_node,
 				       const struct device_node *target_base)
 {
 	struct device_node *node;
-	char *target_path;
 	const char *path;
 	u32 val;
 	int ret;
@@ -709,23 +712,14 @@ static struct device_node *find_target(const struct device_node *info_node,
 
 	ret = of_property_read_string(info_node, "target-path", &path);
 	if (!ret) {
-		if (target_base) {
-			target_path = kasprintf(GFP_KERNEL, "%pOF%s", target_base, path);
-			if (!target_path)
-				return NULL;
-			node = of_find_node_by_path(target_path);
-			if (!node) {
-				pr_err("find target, node: %pOF, path '%s' not found\n",
-				       info_node, target_path);
-			}
-			kfree(target_path);
-		} else {
-			node =  of_find_node_by_path(path);
-			if (!node) {
-				pr_err("find target, node: %pOF, path '%s' not found\n",
-				       info_node, path);
-			}
-		}
+		/* an empty target-path means the target base itself */
+		if (target_base && path[0] == '\0')
+			return of_node_get((struct device_node *)target_base);
+
+		node = of_find_node_by_path(path);
+		if (!node)
+			pr_err("find target, node: %pOF, path '%s' not found\n",
+			       info_node, path);
 		return node;
 	}
 
@@ -737,7 +731,9 @@ static struct device_node *find_target(const struct device_node *info_node,
 /**
  * init_overlay_changeset() - initialize overlay changeset from overlay tree
  * @ovcs:		Overlay changeset to build
- * @target_base:	Point to the target node to apply overlay
+ * @target_base:	Target for fragments with an empty "target-path";
+ *			fragments with a non-empty "target-path" resolve
+ *			absolutely and ignore @target_base
  *
  * Initialize @ovcs.  Populate @ovcs->fragments with node information from
  * the top level of @overlay_root.  The relevant top level nodes are the
@@ -982,7 +978,9 @@ static int of_overlay_apply(struct overlay_changeset *ovcs,
  * @overlay_fdt:	pointer to overlay FDT
  * @overlay_fdt_size:	number of bytes in @overlay_fdt
  * @ret_ovcs_id:	pointer for returning created changeset id
- * @base:		pointer for the target node to apply overlay
+ * @base:		target for fragments with an empty "target-path";
+ *			fragments with a non-empty "target-path" resolve
+ *			absolutely and ignore @base
  *
  * Creates and applies an overlay changeset.
  *

-- 
2.54.0

[PATCH v5 4/9] of/overlay: put property on deadprops only after changeset add succeeds

[Abdurrahman Hussain]

add_changeset_property() links a new property of a not-yet-live
target node into the node's deadprops list before handing it to
of_changeset_add_property(). If that fails, the error path frees the
property but leaves the freed pointer linked in deadprops, and
of_node_release() frees it a second time when the aborted overlay's
node is released.

Record the changeset entry first and link the property into deadprops
only on success. of_changeset_add_property() never looks at the
node's property lists, so the order of the two steps is otherwise
immaterial, and the error path frees a property that nothing
references.

Assisted-by: Claude:claude-fable-5 [Claude Code]
Signed-off-by: Abdurrahman Hussain <abdurrahman@nexthop.ai>
---
 drivers/of/overlay.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
index 74aea704835a..284c9bc6c9cf 100644
--- a/drivers/of/overlay.c
+++ b/drivers/of/overlay.c
@@ -358,12 +358,13 @@ static int add_changeset_property(struct overlay_changeset *ovcs,
 		return -ENOMEM;
 
 	if (!prop) {
-		if (!target->in_livetree) {
+		ret = of_changeset_add_property(&ovcs->cset, target->np,
+						new_prop);
+		/* the detached node owns the property until the apply */
+		if (!ret && !target->in_livetree) {
 			new_prop->next = target->np->deadprops;
 			target->np->deadprops = new_prop;
 		}
-		ret = of_changeset_add_property(&ovcs->cset, target->np,
-						new_prop);
 	} else {
 		ret = of_changeset_update_property(&ovcs->cset, target->np,
 						   new_prop);

-- 
2.54.0

[PATCH v5 5/9] of/overlay: don't keep a negative id in ovcs->id on idr_alloc() failure

[Abdurrahman Hussain]

of_overlay_fdt_apply() stores the idr_alloc() return value in
ovcs->id before checking it. On failure the stored id is negative and
the error path runs free_overlay_changeset(), whose "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.

Reset ovcs->id to 0 before taking the error path.

Fixes: 61b4de4e0b38 ("of: overlay: minor restructuring")
Assisted-by: Claude:claude-fable-5 [Claude Code]
Signed-off-by: Abdurrahman Hussain <abdurrahman@nexthop.ai>
---
 drivers/of/overlay.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
index 284c9bc6c9cf..f1aa8574069a 100644
--- a/drivers/of/overlay.c
+++ b/drivers/of/overlay.c
@@ -1038,6 +1038,8 @@ int of_overlay_fdt_apply(const void *overlay_fdt, u32 overlay_fdt_size,
 	ovcs->id = idr_alloc(&ovcs_idr, ovcs, 1, 0, GFP_KERNEL);
 	if (ovcs->id <= 0) {
 		ret = ovcs->id;
+		/* free_overlay_changeset() treats a set id as registered */
+		ovcs->id = 0;
 		goto err_free_ovcs;
 	}
 

-- 
2.54.0

[PATCH v5 6/9] of/overlay: don't create "//" paths for fragments targeting the root

[Abdurrahman Hussain]

dup_and_fixup_symbol_prop() rewrites a symbol value by replacing its
"/fragment/__overlay__" prefix with the fragment's target path. When
the fragment targets the root node the target path is "/" and the
result starts with "//", which __of_find_node_by_full_path() cannot
resolve: symbols pointing into such fragments silently stop
resolving.

Drop the target path when it is the root.

Fixes: d1651b03c2df ("of: overlay: add overlay symbols to live device tree")
Assisted-by: Claude:claude-fable-5 [Claude Code]
Signed-off-by: Abdurrahman Hussain <abdurrahman@nexthop.ai>
---
 drivers/of/overlay.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
index f1aa8574069a..c6962e9948cc 100644
--- a/drivers/of/overlay.c
+++ b/drivers/of/overlay.c
@@ -256,6 +256,9 @@ static struct property *dup_and_fixup_symbol_prop(
 	if (!target_path)
 		return NULL;
 	target_path_len = strlen(target_path);
+	/* a root target renders as "/"; drop it to avoid "//" results */
+	if (target_path_len == 1 && target_path[0] == '/')
+		target_path_len = 0;
 
 	new_prop = kzalloc_obj(*new_prop);
 	if (!new_prop)

-- 
2.54.0

[PATCH v5 7/9] of/overlay: return ERR_PTR from dup_and_fixup_symbol_prop()

[Abdurrahman Hussain]

dup_and_fixup_symbol_prop() returns NULL for malformed values, for
values that are not paths into one of the overlay's fragments, and
for allocation failures. The caller reports all of them as -ENOMEM,
so a structural problem in /__symbols__ is diagnosed as memory
exhaustion.

A later patch reuses the helper for /aliases values and must handle
the three cases differently: copy verbatim, warn, or fail the apply.
Return ERR_PTR(-EINVAL), ERR_PTR(-ENODEV) and ERR_PTR(-ENOMEM)
respectively and propagate the errno in the /__symbols__ caller.

Also verify that the value descends through the matched fragment's
__overlay__ node before cutting the prefix. Only the first path
component was resolved, so an absolute live-tree value sharing its
first component with a fragment name was sliced at the prefix length
and rewritten to garbage. A prefix mismatch returns -ENODEV.

Assisted-by: Claude:claude-fable-5 [Claude Code]
Signed-off-by: Abdurrahman Hussain <abdurrahman@nexthop.ai>
---
 drivers/of/overlay.c | 35 ++++++++++++++++++++++++++---------
 1 file changed, 26 insertions(+), 9 deletions(-)

diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
index c6962e9948cc..1a2df83fbd8d 100644
--- a/drivers/of/overlay.c
+++ b/drivers/of/overlay.c
@@ -206,6 +206,10 @@ static void overlay_fw_devlink_refresh(struct overlay_changeset *ovcs)
  * The duplicated property value will be modified by replacing the
  * "/fragment_name/__overlay/" portion of the value  with the target
  * path from the fragment node.
+ *
+ * Return: the fixed-up property, or ERR_PTR: -EINVAL if @prop's value
+ * is not a valid non-empty C string, -ENODEV if it is not a path into
+ * one of @ovcs's fragments, -ENOMEM on allocation failure.
  */
 static struct property *dup_and_fixup_symbol_prop(
 		struct overlay_changeset *ovcs, const struct property *prop)
@@ -217,6 +221,8 @@ static struct property *dup_and_fixup_symbol_prop(
 	const char *path;
 	const char *path_tail;
 	const char *target_path;
+	char *overlay_name;
+	bool mismatch;
 	int k;
 	int overlay_name_len;
 	int path_len;
@@ -224,14 +230,14 @@ static struct property *dup_and_fixup_symbol_prop(
 	int target_path_len;
 
 	if (!prop->value)
-		return NULL;
+		return ERR_PTR(-EINVAL);
 	if (strnlen(prop->value, prop->length) >= prop->length)
-		return NULL;
+		return ERR_PTR(-EINVAL);
 	path = prop->value;
 	path_len = strlen(path);
 
 	if (path_len < 1)
-		return NULL;
+		return ERR_PTR(-EINVAL);
 	fragment_node = __of_find_node_by_path(ovcs->overlay_root, path + 1);
 	overlay_node = __of_find_node_by_path(fragment_node, "__overlay__/");
 	of_node_put(fragment_node);
@@ -243,18 +249,27 @@ static struct property *dup_and_fixup_symbol_prop(
 			break;
 	}
 	if (k >= ovcs->count)
-		return NULL;
+		return ERR_PTR(-ENODEV);
+
+	overlay_name = kasprintf(GFP_KERNEL, "%pOF", fragment->overlay);
+	if (!overlay_name)
+		return ERR_PTR(-ENOMEM);
+	overlay_name_len = strlen(overlay_name);
 
-	overlay_name_len = snprintf(NULL, 0, "%pOF", fragment->overlay);
+	/* @path must descend through this fragment's __overlay__ node */
+	mismatch = overlay_name_len > path_len ||
+		   strncmp(path, overlay_name, overlay_name_len) != 0 ||
+		   (path[overlay_name_len] != '/' && path[overlay_name_len]);
+	kfree(overlay_name);
+	if (mismatch)
+		return ERR_PTR(-ENODEV);
 
-	if (overlay_name_len > path_len)
-		return NULL;
 	path_tail = path + overlay_name_len;
 	path_tail_len = strlen(path_tail);
 
 	target_path = kasprintf(GFP_KERNEL, "%pOF", fragment->target);
 	if (!target_path)
-		return NULL;
+		return ERR_PTR(-ENOMEM);
 	target_path_len = strlen(target_path);
 	/* a root target renders as "/"; drop it to avoid "//" results */
 	if (target_path_len == 1 && target_path[0] == '/')
@@ -284,7 +299,7 @@ static struct property *dup_and_fixup_symbol_prop(
 err_free_target_path:
 	kfree(target_path);
 
-	return NULL;
+	return ERR_PTR(-ENOMEM);
 }
 
 /**
@@ -353,6 +368,8 @@ static int add_changeset_property(struct overlay_changeset *ovcs,
 		if (prop)
 			return -EINVAL;
 		new_prop = dup_and_fixup_symbol_prop(ovcs, overlay_prop);
+		if (IS_ERR(new_prop))
+			return PTR_ERR(new_prop);
 	} else {
 		new_prop = __of_prop_dup(overlay_prop, GFP_KERNEL);
 	}

-- 
2.54.0

[PATCH v5 8/9] of/overlay: rewrite /aliases path values to live-tree paths

[Abdurrahman Hussain]

An /aliases property added by an overlay references labeled nodes as
"&label", which dtc renders as an overlay-internal path such as
"/fragment@1/__overlay__/i2c@40000". The value is copied verbatim
into the live tree, of_find_node_by_path() cannot resolve it, and
of_alias_get_id() keeps returning -ENODEV.

/__symbols__ values follow the same convention and are already
rewritten by dup_and_fixup_symbol_prop(). Use it for properties of
the /aliases node too:

  - a value that resolves inside one of the overlay's fragments is
    stored rewritten to the live-tree path
  - -ENODEV (legacy string aliases, absolute live-tree paths) is
    copied verbatim, as before this series
  - -EINVAL (not a NUL-terminated string) is copied verbatim with a
    warning; consumers validate before dereferencing, and an overlay
    that applied before this series keeps applying
  - only -ENOMEM fails the apply

Pseudo-properties are exempt: the is_pseudo_property() check at the
top of add_changeset_property() only covers live-tree targets, and a
phandle of a newly created /aliases node is a cell, not a string.

Assisted-by: Claude:claude-fable-5 [Claude Code]
Signed-off-by: Abdurrahman Hussain <abdurrahman@nexthop.ai>
---
 drivers/of/overlay.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
index 1a2df83fbd8d..27a460daeed9 100644
--- a/drivers/of/overlay.c
+++ b/drivers/of/overlay.c
@@ -370,6 +370,19 @@ static int add_changeset_property(struct overlay_changeset *ovcs,
 		new_prop = dup_and_fixup_symbol_prop(ovcs, overlay_prop);
 		if (IS_ERR(new_prop))
 			return PTR_ERR(new_prop);
+	} else if (!is_pseudo_property(overlay_prop->name) &&
+		   of_node_is_aliases(target->np)) {
+		/* rewrite overlay-internal alias values to live-tree paths */
+		new_prop = dup_and_fixup_symbol_prop(ovcs, overlay_prop);
+		if (new_prop == ERR_PTR(-ENOMEM))
+			return -ENOMEM;
+		if (IS_ERR(new_prop)) {
+			if (new_prop == ERR_PTR(-EINVAL))
+				pr_warn("%pOF/%s is not a valid string; alias will be inert\n",
+					target->np, overlay_prop->name);
+			/* not overlay-internal: copy verbatim, consumers validate */
+			new_prop = __of_prop_dup(overlay_prop, GFP_KERNEL);
+		}
 	} else {
 		new_prop = __of_prop_dup(overlay_prop, GFP_KERNEL);
 	}

-- 
2.54.0

[PATCH v5 9/9] of: unittest: cover /aliases updates from overlay apply/revert

[Abdurrahman Hussain]

Add overlay_alias.dtso and of_unittest_overlay_alias().

The overlay has two fragments: target-path="" grafts a labeled node
under the run-time target base, and target-path="/aliases" adds
`testcase-alias99 = &<label>` at the DT root. The runner applies it
with a non-NULL base via of_overlay_fdt_apply() (overlay_data_apply()
always passes NULL), asserts of_alias_get_id() on the grafted node
returns 99, reverts, and asserts of_alias_get_highest_id() reports
the stem gone. A precondition check runs before the apply.

This exercises the reconfig notifier, the absolute target-path
lookup, and the /aliases value rewrite together; any one missing
turns the get_id assertion into -ENODEV.

The grafted-node reference is dropped before of_overlay_remove():
overlay-created nodes must be back at refcount 1 when the changeset
is destroyed. The post-remove assertion uses of_alias_get_highest_id()
because it is keyed by stem and needs no node reference. The apply is
wrapped in EXPECT_BEGIN/END for the "memory leak will occur" warning
printed for properties added to nodes the overlay didn't create,
like the other overlay tests.

The overlay is not added to the fdtoverlay static build test:
fdtoverlay has no target-base concept, so the empty target-path
cannot be resolved statically.

Assisted-by: Claude:claude-fable-5 [Claude Code]
Signed-off-by: Abdurrahman Hussain <abdurrahman@nexthop.ai>
---
 drivers/of/unittest-data/Makefile           |  5 ++
 drivers/of/unittest-data/overlay_alias.dtso | 25 ++++++++++
 drivers/of/unittest.c                       | 73 +++++++++++++++++++++++++++++
 3 files changed, 103 insertions(+)

diff --git a/drivers/of/unittest-data/Makefile b/drivers/of/unittest-data/Makefile
index 01a966e39f23..fdfec5a7923b 100644
--- a/drivers/of/unittest-data/Makefile
+++ b/drivers/of/unittest-data/Makefile
@@ -22,6 +22,7 @@ obj-$(CONFIG_OF_OVERLAY) += overlay.dtbo.o \
 			    overlay_18.dtbo.o \
 			    overlay_19.dtbo.o \
 			    overlay_20.dtbo.o \
+			    overlay_alias.dtbo.o \
 			    overlay_bad_add_dup_node.dtbo.o \
 			    overlay_bad_add_dup_prop.dtbo.o \
 			    overlay_bad_phandle.dtbo.o \
@@ -66,6 +67,10 @@ DTC_FLAGS_testcases += -Wno-interrupts_property \
 #			  overlay_bad_add_dup_prop.dtbo \
 #			  overlay_bad_phandle.dtbo \
 #			  overlay_bad_symbol.dtbo \
+#
+# overlay_alias.dtbo needs a run-time target base for its empty target-path;
+# fdtoverlay has no equivalent, so it is also not included:
+#			  overlay_alias.dtbo \
 
 apply_static_overlay_1 := overlay_0.dtbo \
 			  overlay_1.dtbo \
diff --git a/drivers/of/unittest-data/overlay_alias.dtso b/drivers/of/unittest-data/overlay_alias.dtso
new file mode 100644
index 000000000000..17e02d1940f6
--- /dev/null
+++ b/drivers/of/unittest-data/overlay_alias.dtso
@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: GPL-2.0
+/dts-v1/;
+/plugin/;
+
+/*
+ * overlay_alias - declare an /aliases entry that points, via label, at a
+ * node grafted under the run-time target base (empty target-path).
+ */
+
+/ {
+	fragment@0 {
+		target-path = "";
+		__overlay__ {
+			testcase_target: alias-target {
+			};
+		};
+	};
+
+	fragment@1 {
+		target-path = "/aliases";
+		__overlay__ {
+			testcase-alias99 = &testcase_target;
+		};
+	};
+};
diff --git a/drivers/of/unittest.c b/drivers/of/unittest.c
index e255f54f4d76..2f5e4056efae 100644
--- a/drivers/of/unittest.c
+++ b/drivers/of/unittest.c
@@ -3475,6 +3475,77 @@ static struct notifier_block of_nb = {
 	.notifier_call = of_notify,
 };
 
+/* created by cmd_wrap_S_dtbo in scripts/Makefile.dtbs */
+extern uint8_t __dtbo_overlay_alias_begin[];
+extern uint8_t __dtbo_overlay_alias_end[];
+
+static void __init of_unittest_overlay_alias(void)
+{
+	const char *base_path =
+		"/testcase-data/overlay-node/test-bus/test-unittest100";
+	const char *target_path =
+		"/testcase-data/overlay-node/test-bus/test-unittest100/alias-target";
+	u32 size = __dtbo_overlay_alias_end - __dtbo_overlay_alias_begin;
+	struct device_node *base, *target;
+	int ovcs_id = 0;
+	int id, ret;
+
+	base = of_find_node_by_path(base_path);
+	if (!base) {
+		unittest(0, "could not find alias target base %s\n", base_path);
+		return;
+	}
+
+	id = of_alias_get_highest_id("testcase-alias");
+	if (id != -ENODEV) {
+		unittest(0, "unexpected testcase-alias%d before overlay apply\n",
+			 id);
+		goto out_put_base;
+	}
+
+	EXPECT_BEGIN(KERN_INFO,
+		     "OF: overlay: WARNING: memory leak will occur if overlay removed, property: /aliases/testcase-alias99");
+
+	ret = of_overlay_fdt_apply(__dtbo_overlay_alias_begin, size,
+				   &ovcs_id, base);
+
+	EXPECT_END(KERN_INFO,
+		   "OF: overlay: WARNING: memory leak will occur if overlay removed, property: /aliases/testcase-alias99");
+
+	if (ret < 0) {
+		unittest(0, "overlay_alias apply failed, ret = %d\n", ret);
+		if (ovcs_id)
+			of_overlay_remove(&ovcs_id);
+		goto out_put_base;
+	}
+
+	target = of_find_node_by_path(target_path);
+	if (!target) {
+		unittest(0, "could not find grafted target %s\n", target_path);
+	} else {
+		id = of_alias_get_id(target, "testcase-alias");
+		unittest(id == 99,
+			 "of_alias_get_id() = %d after overlay apply, expected 99\n",
+			 id);
+		/* changeset destroy expects overlay nodes back at refcount 1 */
+		of_node_put(target);
+	}
+
+	ret = of_overlay_remove(&ovcs_id);
+	if (ret) {
+		unittest(0, "overlay_alias remove failed, ret = %d\n", ret);
+		goto out_put_base;
+	}
+
+	id = of_alias_get_highest_id("testcase-alias");
+	unittest(id == -ENODEV,
+		 "of_alias_get_highest_id() = %d after overlay remove, expected -ENODEV\n",
+		 id);
+
+out_put_base:
+	of_node_put(base);
+}
+
 static void __init of_unittest_overlay_notify(void)
 {
 	int ovcs_id;
@@ -3649,6 +3720,8 @@ static void __init of_unittest_overlay(void)
 
 	of_unittest_overlay_gpio();
 
+	of_unittest_overlay_alias();
+
 	of_unittest_remove_tracked_overlays();
 
 	of_unittest_overlay_notify();

-- 
2.54.0

Re: [PATCH v5 2/9] of: update /aliases lookup on reconfig notifications

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [High] Lockless iteration over `aliases->properties` in `of_find_node_opts_by_path()` races with concurrent property additions/removals.
--

--- Patch [2]: [PATCH v5 2/9] of: update /aliases lookup on reconfig notifications ---
commit 9797d916f1b83a48a93f588ed426470feb4bed4a
Author: Abdurrahman Hussain <abdurrahman@nexthop.ai>

of: update /aliases lookup on reconfig notifications
    
Registers a reconfig notifier to mirror /aliases property changes into
aliases_lookup. The notifier chain covers changesets and overlays, matching
the /aliases node by name and root parent.

Link: https://lore.kernel.org/lkml/1435675876-2159-1-git-send-email-geert+renesas@glider.be/
Link: https://lore.kernel.org/lkml/20150630172131.D4E6CC4041A@trevor.secretlab.ca/

> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index 6f79f593fc779..612e2cd31688d 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
[ ... ]
> +	case OF_RECONFIG_ADD_PROPERTY:
> +		of_alias_create(rd->prop, alias_alloc, true);
> +		break;
> +	case OF_RECONFIG_REMOVE_PROPERTY:
> +		of_alias_destroy(rd->prop->name);
> +		break;
> +	case OF_RECONFIG_UPDATE_PROPERTY:
> +		if (rd->old_prop)
> +			of_alias_destroy(rd->old_prop->name);
> +		of_alias_create(rd->prop, alias_alloc, true);
> +		break;

[Severity: High]
This isn't a bug introduced by this patch, but can this concurrent property
addition or removal race with the lockless property iteration in
of_find_node_opts_by_path()?

In drivers/of/base.c:of_find_node_opts_by_path(), aliases->properties is
iterated locklessly:

		for_each_property_of_node(aliases, pp) {
			if (!strncmp(pp->name, path, len) && !pp->name[len]) {
				if (of_alias_value_ok(pp))
					value = pp->value;
				break;
			}
		}

Concurrent property modifications via __of_add_property() or
__of_update_property() manipulate the list pointers without memory barriers.
A lockless reader may traverse to a newly added property before its contents
(like pp->name) are globally visible, leading to a crash. Additionally,
__of_update_property() repoints oldprop->next to deadprops, which can divert
a lockless reader into the dead properties list.

Could taking devtree_lock during the iteration, or utilizing the newly
synchronized aliases_lookup list, prevent this race?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260722-nh-of-alias-overlay-v5-0-2abe2bb9cdbc@nexthop.ai?part=2

Re: [PATCH v5 6/9] of/overlay: don't create "//" paths for fragments targeting the root

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider:

New issues:
- [Medium] Unconditionally dropping the "/" target path generates an invalid empty string "" for symbols referencing the root of a root-targeted overlay fragment.

Pre-existing issues:
- [Medium] Device node reference count leak in init_overlay_changeset() on error path.
- [Medium] Memory and reference count leak of duplicated device node in add_changeset_node().
--

--- Patch [6]: [PATCH v5 6/9] of/overlay: don't create "//" paths for fragments targeting the root ---
commit aa0fca741484513e2136984fcef43c90b2ab9e9a
Author: Abdurrahman Hussain <abdurrahman@nexthop.ai>

of/overlay: don't create "//" paths for fragments targeting the root

dup_and_fixup_symbol_prop() rewrites a symbol value by replacing its
"/fragment/__overlay__" prefix with the fragment's target path. When
the fragment targets the root node the target path is "/" and the
result starts with "//", which __of_find_node_by_full_path() cannot
resolve: symbols pointing into such fragments silently stop
resolving.

> diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
> index f1aa8574069a6..c6962e9948cc9 100644
> --- a/drivers/of/overlay.c
> +++ b/drivers/of/overlay.c
> @@ -256,6 +256,9 @@ static struct property *dup_and_fixup_symbol_prop(
>  	if (!target_path)
>  		return NULL;
>  	target_path_len = strlen(target_path);
> +	/* a root target renders as "/"; drop it to avoid "//" results */
> +	if (target_path_len == 1 && target_path[0] == '/')
> +		target_path_len = 0;
>  
>  	new_prop = kzalloc_obj(*new_prop);
>  	if (!new_prop)

[Severity: Medium]
When path_tail_len is 0 (i.e. a symbol referencing the root of a root-targeted
overlay fragment), wouldn't unconditionally clearing target_path_len result in
an empty string "" instead of a valid path?

If path_tail is empty, should we preserve the root "/" target?

[Severity: Medium]
This is a pre-existing issue, but does this error path in
init_overlay_changeset() leak the successfully initialized fragment references?

drivers/of/overlay.c:init_overlay_changeset() {
    ...
		fragment->target = find_target(node, target_base);
		if (!fragment->target) {
			of_node_put(fragment->overlay);
			ret = -EINVAL;
			of_node_put(node);
			goto err_out;
		}
    ...
}

If a later fragment fails to find its target, the function jumps to err_out
without saving the processed fragment count to ovcs->count. As a result,
free_overlay_changeset() will skip cleaning up the leaked nodes.

[Severity: Medium]
This is a pre-existing issue, but is it possible for add_changeset_node() to
leak the dynamically allocated tchild device node on attachment failure?

drivers/of/overlay.c:add_changeset_node() {
    ...
	if (!tchild) {
		tchild = __of_node_dup(NULL, node_kbasename);
        ...
		ret = of_changeset_attach_node(&ovcs->cset, tchild);
		if (ret)
			return ret;
    ...
}

When of_changeset_attach_node() fails, it returns directly, skipping the
necessary of_node_put(tchild) call and leaking the node.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260722-nh-of-alias-overlay-v5-0-2abe2bb9cdbc@nexthop.ai?part=6

Re: [PATCH v5 1/9] of: hold a reference on of_aliases during alias path resolution

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:

Pre-existing issues:
- [High] Calling of_node_put() while holding a raw spinlock causes a sleep-in-atomic bug if it drops the last reference to a dynamic node.
- [High] Lockless iteration of device tree properties is unsafe because updated or removed properties have their `next` pointer modified, which derails concurrent readers.
--

--- Patch [1]: [PATCH v5 1/9] of: hold a reference on of_aliases during alias path resolution ---
commit aa90279de0a9f76f84e2b40b29743f11984c3ffb
Author: Abdurrahman Hussain <abdurrahman@nexthop.ai>
Subject: of: hold a reference on of_aliases during alias path resolution

This patch modifies of_find_node_opts_by_path to hold a reference to
of_aliases during alias path resolution. It also validates the alias value
to prevent crashes or infinite recursion with malformed device trees.

> Take a reference across the walk. The walk itself stays lock-free
> like every other property iteration: removed properties keep their
> ->next and are only freed when the node is released, so the node
> reference is sufficient.

[Severity: High]
This isn't a bug introduced by this patch, but is the description of the
lock-free walk accurate?

Looking at __of_remove_property() and __of_update_property(), when a
property is removed, it is moved to the node's deadprops list:

drivers/of/base.c:__of_remove_property() {
    ...
    /* Found the property, add it to deadprops list */
    prop->next = np->deadprops;
    np->deadprops = prop;
    ...
}

If a concurrent writer (e.g., overlay application) removes a property while
for_each_property_of_node() is iterating over it, won't the reader's next
access of pp->next follow the pointer into the deadprops list? 

This would cause the reader to traverse the dead properties and skip the
remaining valid properties in np->properties, potentially causing spurious
lookup failures.

> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index 6e7a42dedad3f..6f79f593fc779 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c

[ ... ]

> @@ -1002,16 +1004,24 @@ struct device_node *of_find_node_opts_by_path(const char *path, const char **opt
>  			p = separator;
>  		len = p - path;
>  
> -		/* of_aliases must not be NULL */
> -		if (!of_aliases)
> +		/* the load pairs with writers that retire the node */
> +		raw_spin_lock_irqsave(&devtree_lock, flags);
> +		aliases = of_node_get(of_aliases);
> +		raw_spin_unlock_irqrestore(&devtree_lock, flags);
> +		if (!aliases)
>  			return NULL;
>  
> -		for_each_property_of_node(of_aliases, pp) {
> -			if (strlen(pp->name) == len && !strncmp(pp->name, path, len)) {
> -				np = of_find_node_by_path(pp->value);
> +		for_each_property_of_node(aliases, pp) {
> +			if (!strncmp(pp->name, path, len) && !pp->name[len]) {
> +				if (of_alias_value_ok(pp))
> +					value = pp->value;
>  				break;
>  			}
>  		}
> +		/* the reference on @aliases keeps @value alive */
> +		if (value)
> +			np = of_find_node_by_path(value);
> +		of_node_put(aliases);
>  		if (!np)
>  			return NULL;
>  		path = p;

[Severity: High]
This is a pre-existing issue, but does calling __of_find_node_by_full_path()
while holding devtree_lock further down in this function risk a
sleep-in-atomic bug?

Right after this block in of_find_node_opts_by_path(), devtree_lock (which is
a raw spinlock) is acquired around __of_find_node_by_full_path():

drivers/of/base.c:of_find_node_opts_by_path() {
    ...
    /* Step down the tree matching path components */
    raw_spin_lock_irqsave(&devtree_lock, flags);
    if (!np)
        np = of_node_get(of_root);
    np = __of_find_node_by_full_path(np, path);
    raw_spin_unlock_irqrestore(&devtree_lock, flags);
    ...
}

Inside __of_find_node_by_full_path(), it iteratively drops node references:

drivers/of/base.c:__of_find_node_by_full_path() {
    ...
    node = __of_find_node_by_path(node, path);
    of_node_put(tmp);
    ...
}

If a parallel thread (such as an overlay removal) detaches a dynamic node,
its primary tree reference is dropped.

If of_node_put() drops the last reference to that node while held under the
raw spinlock, won't it synchronously invoke of_node_release()?

For dynamic nodes, of_node_release() calls fwnode_links_purge(), which
acquires fwnode_link_lock (a sleeping mutex), resulting in a sleep-in-atomic
scenario.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260722-nh-of-alias-overlay-v5-0-2abe2bb9cdbc@nexthop.ai?part=1

Re: [PATCH v5 5/9] of/overlay: don't keep a negative id in ovcs->id on idr_alloc() failure

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider:

Pre-existing issues:
- [High] This problem wasn't introduced by this patch, but callers of `of_overlay_fdt_apply()` fail to call `of_overlay_remove()` when the application fails, leading to a memory leak.
- [High] This problem wasn't introduced by this patch, but if `of_changeset_attach_node()` fails in `add_changeset_node()`, the newly allocated device node `tchild` is permanently leaked.
- [High] This problem wasn't introduced by this patch, but if `init_overlay_changeset()` fails after successfully parsing one or more fragments, the OF node references for those initialized fragments are leaked.
--

--- Patch [5]: [PATCH v5 5/9] of/overlay: don't keep a negative id in ovcs->id on idr_alloc() failure ---
commit bdff881a51ac56990164b0a5479bf6e47e64305a
Author: Abdurrahman Hussain <abdurrahman@nexthop.ai>

    of/overlay: don't keep a negative id in ovcs->id on idr_alloc() failure

This commit fixes a bug where a negative return value from idr_alloc()
is stored in ovcs->id. On the error path, free_overlay_changeset() checks
if ovcs->id is non-zero, leading to idr_remove() being called with a
negative id and list_del() operating on an uninitialized list.

> diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
> index 284c9bc6c9cfc..f1aa8574069a6 100644
> --- a/drivers/of/overlay.c
> +++ b/drivers/of/overlay.c
> @@ -1038,6 +1038,8 @@ int of_overlay_fdt_apply(const void *overlay_fdt, u32 overlay_fdt_size,
>  	ovcs->id = idr_alloc(&ovcs_idr, ovcs, 1, 0, GFP_KERNEL);
>  	if (ovcs->id <= 0) {
>  		ret = ovcs->id;
> +		/* free_overlay_changeset() treats a set id as registered */
> +		ovcs->id = 0;
>  		goto err_free_ovcs;
>  	}

[Severity: High]
This isn't a bug introduced by this patch, but callers of
of_overlay_fdt_apply() fail to call of_overlay_remove() when the
application fails, leading to a memory leak.

If of_overlay_apply() fails inside of_overlay_fdt_apply(), the function
intentionally leaves the returned changeset ID set via the pointer,
expecting the caller to handle cleanup by calling of_overlay_remove().
However, callers simply return the error code upon failure without
calling of_overlay_remove().

For example, in tilcdc_panel_legacy_probe():

drivers/gpu/drm/tilcdc/tilcdc_panel_legacy.c:tilcdc_panel_legacy_probe() {
    ...
	ret = of_overlay_fdt_apply(dtbo_start, dtbo_size, &ovcs_id, NULL);
	if (ret)
		return ret;
    ...
}

And in lan966x_pci_probe():

drivers/misc/lan966x_pci.c:lan966x_pci_probe() {
    ...
	ret = lan966x_pci_load_overlay(data);
	if (ret)
		return ret;
    ...
}

The helper returns the result directly to lan966x_pci_probe(), which bails
on error without invoking the corresponding lan966x_pci_unload_overlay().

Can this result in a permanent memory and ID leak of the overlay changeset,
especially since probe functions can be repeatedly triggered via sysfs
bind/unbind or deferred probing?


[Severity: High]
This isn't a bug introduced by this patch, but if of_changeset_attach_node()
fails in add_changeset_node(), is the newly allocated device node
permanently leaked?

In add_changeset_node(), __of_node_dup() creates a new node (tchild) with a
reference count of 1:

drivers/of/overlay.c:add_changeset_node() {
    ...
		ret = of_changeset_attach_node(&ovcs->cset, tchild);
		if (ret)
			return ret;
    ...
}

If of_changeset_attach_node() fails, the function returns the error
immediately without dropping the reference to tchild via of_node_put().

Could this leak the device node structure and its associated name string?


[Severity: High]
This isn't a bug introduced by this patch, but if init_overlay_changeset()
fails after successfully parsing one or more fragments, are the OF node
references for those initialized fragments leaked?

In init_overlay_changeset(), the function iterates over overlay fragments
and acquires references via of_get_child_by_name() and find_target(). If
find_target() fails for a subsequent fragment, it jumps to err_out without
dropping the current overlay_node reference or updating ovcs->count:

drivers/of/overlay.c:init_overlay_changeset() {
    ...
		fragment->target = find_target(node, target_base);
		if (!fragment->target) {
			of_node_put(node);
			ret = -EINVAL;
			goto err_out;
		}
    ...
}

Because ovcs->count remains 0, free_overlay_changeset() skips the cleanup
loop entirely:

drivers/of/overlay.c:free_overlay_changeset() {
    ...
	for (i = 0; i < ovcs->count; i++) {
		of_node_put(ovcs->fragments[i].target);
		of_node_put(ovcs->fragments[i].overlay);
	}
    ...
}

Could this skip cleanup and leak the successfully acquired OF nodes from
previous iterations?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260722-nh-of-alias-overlay-v5-0-2abe2bb9cdbc@nexthop.ai?part=5