[PATCH v2 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) and computes
content_len = dir_len - 4.  If a crafted peer supplies
entry->length < 4, the subtraction underflows size_t to ~SIZE_MAX,
nentries becomes SIZE_MAX / 4, and the entry walk runs off the
property block, reading OOB on each iteration until either an entry
fails validation or the kernel oopses on an unmapped page.

Reject dir_len < 4 explicitly before the subtraction.

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

Fixes: e69b6c02b4c3 ("thunderbolt: Add functions for parsing and creating XDomain property blocks")
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 | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/thunderbolt/property.c b/drivers/thunderbolt/property.c
index f5ee8f531300..274b555d27c8 100644
--- a/drivers/thunderbolt/property.c
+++ b/drivers/thunderbolt/property.c
@@ -173,6 +173,7 @@ static struct tb_property_dir *__tb_property_parse_dir(const u32 *block,
 	dir = kzalloc_obj(*dir);
 	if (!dir)
 		return NULL;
+	INIT_LIST_HEAD(&dir->properties);
 
 	if (is_root) {
 		content_offset = dir_offset + 2;
@@ -184,6 +185,10 @@ static struct tb_property_dir *__tb_property_parse_dir(const u32 *block,
 			tb_property_free_dir(dir);
 			return NULL;
 		}
+		if (dir_len < 4) {
+			tb_property_free_dir(dir);
+			return NULL;
+		}
 		content_offset = dir_offset + 4;
 		content_len = dir_len - 4; /* Length includes UUID */
 	}
@@ -191,8 +196,6 @@ 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