[PATCH v3 1/4] thunderbolt: property: reject u32 wrap in tb_property_entry_valid()

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

entry->value is u32 and entry->length is u16; the sum is performed in
u32 and wraps.  A malicious XDomain peer can pick
value = 0xffffff00, length = 0x100 so the sum 0x100000000 wraps to 0
and passes the > block_len check.  tb_property_parse() then passes
entry->value to parse_dwdata() as a dword offset into the property
block, reading attacker-directed memory far past the allocation.

For TEXT-typed entries with the "deviceid" or "vendorid" keys this
lands in xd->device_name / xd->vendor_name and is readable back via
the per-XDomain device_name / vendor_name sysfs attributes; the leak
is NUL-bounded (kstrdup() stops at the first zero byte) and
untargeted (the attacker picks a delta, not an absolute address).
DATA-typed entries are parsed into property->value.data but not
generically surfaced to userspace.

Use check_add_overflow() so a wrapped sum is rejected.

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>
---
v2 -> v3 (no code changes):
- Lowercase 0xffffff00 in commit message.
- Fix Fixes: SHA (was e69b6c02b4c3, "net: Add support for
  networking over Thunderbolt cable"; correct is cdae7c07e3e3).

 drivers/thunderbolt/property.c | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/drivers/thunderbolt/property.c b/drivers/thunderbolt/property.c
index 50cbfc92fe65..f5ee8f531300 100644
--- a/drivers/thunderbolt/property.c
+++ b/drivers/thunderbolt/property.c
@@ -8,6 +8,7 @@
  */
 
 #include <linux/err.h>
+#include <linux/overflow.h>
 #include <linux/slab.h>
 #include <linux/string.h>
 #include <linux/uuid.h>
@@ -52,13 +53,16 @@ static inline void format_dwdata(void *dst, const void *src, size_t dwords)
 static bool tb_property_entry_valid(const struct tb_property_entry *entry,
 				  size_t block_len)
 {
+	u32 end;
+
 	switch (entry->type) {
 	case TB_PROPERTY_TYPE_DIRECTORY:
 	case TB_PROPERTY_TYPE_DATA:
 	case TB_PROPERTY_TYPE_TEXT:
 		if (entry->length > block_len)
 			return false;
-		if (entry->value + entry->length > block_len)
+		if (check_add_overflow(entry->value, (u32)entry->length, &end) ||
+		    end > block_len)
 			return false;
 		break;
 
-- 
2.53.0