[PATCH v4 2/4] thunderbolt: property: reject dir_len < 4 to prevent size_t underflow

[Michael Bommarito <michael.bommarito@gmail.com>]

On the non-root path, __tb_property_parse_dir() takes dir_len from
entry->length (u16 widened to size_t).  Two distinct OOB conditions
follow when entry->length < 4:

1. The non-root path begins with kmemdup(&block[dir_offset],
   sizeof(*dir->uuid), ...) which always reads 4 dwords from
   dir_offset.  tb_property_entry_valid() only enforces
   dir_offset + entry->length <= block_len, so a crafted entry
   with dir_offset close to the end of the property block and
   entry->length in 0..3 passes that gate but lets the UUID copy
   run off the block (e.g. dir_offset = 497, dir_len = 3 in a
   500-dword block reads block[497..501]).

2. After the kmemdup, content_len = dir_len - 4 underflows size_t
   to ~SIZE_MAX, nentries becomes SIZE_MAX / 4, and the entry
   walk runs OOB on each iteration until an entry fails
   validation or the kernel oopses on an unmapped page.

Reject dir_len < 4 on the non-root path *before* the UUID kmemdup,
which closes both holes.

Also move INIT_LIST_HEAD(&dir->properties) up to immediately after
the dir allocation so the new error-return path (and the existing
uuid-alloc failure path) calling tb_property_free_dir() sees a
walkable list rather than the zero-initialized NULL next/prev that
list_for_each_entry_safe() would oops on.

Fixes: cdae7c07e3e3 ("thunderbolt: Add support for XDomain properties")
Cc: stable@vger.kernel.org
Assisted-by: Claude:claude-opus-4-6
Assisted-by: Codex:gpt-5-4
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
---
 drivers/thunderbolt/property.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/thunderbolt/property.c b/drivers/thunderbolt/property.c
index 29cd60c11ac4..74c92f9801ff 100644
--- a/drivers/thunderbolt/property.c
+++ b/drivers/thunderbolt/property.c
@@ -174,10 +174,16 @@ static struct tb_property_dir *__tb_property_parse_dir(const u32 *block,
 	if (!dir)
 		return NULL;
 
+	INIT_LIST_HEAD(&dir->properties);
+
 	if (is_root) {
 		content_offset = dir_offset + 2;
 		content_len = dir_len;
 	} else {
+		if (dir_len < 4) {
+			tb_property_free_dir(dir);
+			return NULL;
+		}
 		dir->uuid = kmemdup(&block[dir_offset], sizeof(*dir->uuid),
 				    GFP_KERNEL);
 		if (!dir->uuid) {
@@ -191,8 +197,6 @@ static struct tb_property_dir *__tb_property_parse_dir(const u32 *block,
 	entries = (const struct tb_property_entry *)&block[content_offset];
 	nentries = content_len / (sizeof(*entries) / 4);
 
-	INIT_LIST_HEAD(&dir->properties);
-
 	for (i = 0; i < nentries; i++) {
 		struct tb_property *property;
 
-- 
2.53.0