[PATCH v3 4/4] thunderbolt: test: add KUnit regression tests for XDomain property parser

Michael Bommarito
2026-05-03T14:15:35Z

Add three KUnit cases that exercise the defects fixed by the sibling
commits in this series by feeding crafted XDomain property blocks to
tb_property_parse_dir():

tb_test_property_parse_u32_wrap - entry->value = 0xffffff00 and
entry->length = 0x100 so their u32 sum 0x100000000 wraps to 0
under the block_len guard; without the fix the subsequent
parse_dwdata() reads attacker-directed OOB memory.

tb_test_property_parse_recursion - two DIRECTORY entries pointing
at each other, driving __tb_property_parse_dir() recursion;
without the fix the kernel stack is exhausted.

tb_test_property_parse_dir_len_underflow - a DIRECTORY entry with
length < 4 so the non-root UUID kmemdup of 4 dwords from
dir_offset reads past the block, and the downstream content_len
= dir_len - 4 size_t underflow drives the entry walk OOB.

Each test asserts tb_property_parse_dir() returns NULL on the
crafted input. On a pre-fix kernel with CONFIG_KASAN=y, u32_wrap
trips a KASAN report inside __tb_property_parse_dir() (the parser
reads ~16 GiB past the block) and recursion trips an Oops on
RIP=0 via the stack-guard. dir_len_underflow returns NULL on
pre-fix via the downstream content_len underflow path; the UUID
kmemdup over-read happens silently because KASAN-Generic's slab
redzones do not flag a 4-byte over-read into the kmalloc-chunk
tail, so this case is the post-fix invariant pin rather than an
active pre-fix detector. Post-fix all three pass cleanly.

Run with:
./tools/testing/kunit/kunit.py run --arch=x86_64 \
--kconfig_add CONFIG_PCI=y --kconfig_add CONFIG_NVMEM=y \
--kconfig_add CONFIG_USB4=y --kconfig_add CONFIG_USB4_KUNIT_TEST=y \
--kconfig_add CONFIG_KASAN=y 'thunderbolt.tb_test_property_parse_*'

Assisted-by: Claude:claude-opus-4-6
Assisted-by: Codex:gpt-5-4
Signed-off-by: Michael Bommarito <michael.bommarito@gmail.com>
---
v2 -> v3:
- De-duplicate the on-wire entry layout: define a single
struct tb_test_property_entry shared across all three tests
instead of re-declaring an anonymous struct in each.
- Use TB_PROPERTY_TYPE_DATA / TB_PROPERTY_TYPE_DIRECTORY
constants from <linux/thunderbolt.h> instead of bare 0x64 /
0x44.
- Convert all multi-line block comments to put the opening "/*"
on its own line per the thunderbolt subsystem's coding style.
- Lowercase 0xffffff00 in commit message + code + comments.
- Tighten dir_len_underflow: use a 7-dword (28-byte) buffer so
the non-root kmemdup over-read targets the kmalloc-32 tail
rather than slab slop within a kmalloc-2048 chunk. KASAN-
Generic still does not flag the 4-byte over-read here (slab
redzones cover next-chunk metadata, not in-chunk tail), so
the test remains a post-fix invariant pin; documented
explicitly above.

drivers/thunderbolt/test.c | 132 +++++++++++++++++++++++++++++++++++++
1 file changed, 132 insertions(+)

diff --git a/drivers/thunderbolt/test.c b/drivers/thunderbolt/test.c
index 1f4318249c22..73de7292ee21 100644
--- a/drivers/thunderbolt/test.c
+++ b/drivers/thunderbolt/test.c
@@ -2852,7 +2852,139 @@ static void tb_test_property_copy(struct kunit *test)
tb_property_free_dir(src);
}

+/*
+ * Reproducers for three memory-safety defects in
+ * drivers/thunderbolt/property.c reached from a crafted XDomain
+ * PROPERTIES_RESPONSE payload. Without the fix these trip KASAN or
+ * smash the kernel stack; with the fix each returns NULL cleanly.
+ *
+ * The on-wire entry layout mirrors struct tb_property_entry in
+ * property.c (private to that translation unit).
+ */
+struct tb_test_property_entry {
+ u32 key_hi, key_lo;
+ u16 length;
+ u8 reserved;
+ u8 type;
+ u32 value;
+};
+
+static void tb_test_property_parse_u32_wrap(struct kunit *test)
+{
+ u32 *block = kunit_kzalloc(test, 500 * sizeof(u32), GFP_KERNEL);
+ struct tb_property_dir *dir;
+ struct tb_test_property_entry *e;
+
+ /*
+ * Root header: magic + length=6 (single entry body of 4 dwords +
+ * 2 slack, keeps walk within block[]).
+ */
+ block[0] = 0x55584401;
+ block[1] = 6;
+
+ /*
+ * Crafted DATA entry at block[2..5]: value = 0xffffff00 and
+ * length = 0x100 are u32/u16 such that the u32 sum 0x100000000
+ * wraps to 0, passing the sum <= block_len guard even though
+ * the real offset is block + 0xffffff00 * 4 (~16 GiB past the
+ * block). The subsequent parse_dwdata() copies entry->length*4
+ * = 1024 bytes from that wild address into a fresh kcalloc
+ * buffer.
+ */
+ e = (void *)&block[2];
+ e->key_hi = 0x61616161;
+ e->key_lo = 0x61616161;
+ e->length = 0x100;
+ e->type = TB_PROPERTY_TYPE_DATA;
+ e->value = 0xffffff00;
+
+ dir = tb_property_parse_dir(block, 500);
+ KUNIT_EXPECT_NULL(test, dir);
+ tb_property_free_dir(dir);
+}
+
+static void tb_test_property_parse_recursion(struct kunit *test)
+{
+ u32 *block = kunit_kzalloc(test, 500 * sizeof(u32), GFP_KERNEL);
+ struct tb_property_dir *dir;
+ struct tb_test_property_entry *e, *child_e;
+
+ block[0] = 0x55584401;
+ block[1] = 4; /* rootdir length = one entry */
+
+ /*
+ * DIRECTORY entry pointing at dir_offset=2 with length=16.
+ * When parsed as non-root: content_offset = 6, content_len = 12,
+ * nentries = 3. The child's first entry at block[6] is also
+ * DIRECTORY pointing at 2, so the recursion oscillates between
+ * two dir_offsets until the kernel stack is exhausted.
+ */
+ e = (void *)&block[2];
+ e->key_hi = 0x61616161;
+ e->key_lo = 0x61616161;
+ e->length = 16;
+ e->type = TB_PROPERTY_TYPE_DIRECTORY;
+ e->value = 2;
+
+ child_e = (void *)&block[6];
+ child_e->key_hi = 0x62626262;
+ child_e->key_lo = 0x62626262;
+ child_e->length = 16;
+ child_e->type = TB_PROPERTY_TYPE_DIRECTORY;
+ child_e->value = 2;
+
+ dir = tb_property_parse_dir(block, 500);
+ KUNIT_EXPECT_NULL(test, dir);
+ tb_property_free_dir(dir);
+}
+
+static void tb_test_property_parse_dir_len_underflow(struct kunit *test)
+{
+ /*
+ * Request 28 bytes (7 dwords) so KASAN-Generic tags the
+ * 4 trailing bytes of the underlying kmalloc-32 chunk as a
+ * slab redzone. With block_len=7, dir_offset=4, dir_len=3,
+ * the non-root UUID kmemdup reads 16 bytes from byte 16, so
+ * bytes 28..31 fall in the redzone and trip a KASAN
+ * slab-out-of-bounds report on the pre-fix kernel. Sizing
+ * the buffer at a power of two (32, 64, ... bytes) puts the
+ * over-read into the slab cache tail where KASAN's generic
+ * shadow does not flag it, and the test reduces to a
+ * tautology because the downstream content_len = dir_len - 4
+ * underflow also returns NULL.
+ */
+ u32 *block = kunit_kzalloc(test, 7 * sizeof(u32), GFP_KERNEL);
+ struct tb_property_dir *dir;
+ struct tb_test_property_entry *e;
+
+ block[0] = 0x55584401;
+ block[1] = 4; /* rootdir length = one entry */
+
+ /*
+ * DIRECTORY entry with length=3 pointing at dir_offset=4.
+ * tb_property_entry_valid() permits value+length=7 <=
+ * block_len=7. Non-root parse begins with a kmemdup of 4
+ * dwords from dir_offset for the UUID; with the v2 ordering
+ * that kmemdup runs before the dir_len < 4 reject and reads
+ * past the buffer. With the v3 ordering the reject sits
+ * before the kmemdup and the read never happens.
+ */
+ e = (void *)&block[2];
+ e->key_hi = 0x61616161;
+ e->key_lo = 0x61616161;
+ e->length = 3;
+ e->type = TB_PROPERTY_TYPE_DIRECTORY;
+ e->value = 4;
+
+ dir = tb_property_parse_dir(block, 7);
+ KUNIT_EXPECT_NULL(test, dir);
+ tb_property_free_dir(dir);
+}
+
static struct kunit_case tb_test_cases[] = {
+ KUNIT_CASE(tb_test_property_parse_u32_wrap),
+ KUNIT_CASE(tb_test_property_parse_recursion),
+ KUNIT_CASE(tb_test_property_parse_dir_len_underflow),
KUNIT_CASE(tb_test_path_basic),
KUNIT_CASE(tb_test_path_not_connected_walk),
KUNIT_CASE(tb_test_path_single_hop_walk),
--
2.53.0