Two correctness and type-hygiene issues exist in the DCP trusted keys
implementation.
First, trusted_dcp_unseal() reads p->key_len from a user-supplied blob
without checking if it exceeds MAX_KEY_SIZE. If a crafted blob provides
a payload_len larger than 128, the subsequent do_aead_crypto() call
writes past the end of the p->key array into the adjacent p->blob
buffer within the same struct trusted_key_payload -- the caller's own
input, not unrelated kernel memory. While not exploitable, this
violates strict array bounds and triggers static analyzers. Fix this by adding
a validation check against
MIN_KEY_SIZE and MAX_KEY_SIZE immediately after reading the length,
matching the checks already done in trusted_core.c.
Second, calc_blob_len() calculates a sum in size_t that truncates to
unsigned int on 64-bit platforms. Because the DCP hardware is only
present on 32-bit i.MX SoC platforms, size_t and unsigned int are
functionally equivalent in production, making this truncation harmless in
practice. Nevertheless, updating the return type to size_t (and
subsequently updating 'blen' in the seal/unseal paths) resolves
type-narrowing warnings and improves overall code hygiene.
Fixes: 2e8a0f40a39c ("KEYS: trusted: Introduce NXP DCP-backed trusted keys")
Signed-off-by: Fabrice Derepas <[email protected]>
---
Changes in v2:
- Reframed commit message as correctness/hardening fix (Richard, Jarkko)
- Changed bare return -EINVAL to goto out for consistency
- Added Fixes tag
Compile-tested with arm-linux-gnueabihf-gcc on imx_v6_v7_defconfig
with CONFIG_TRUSTED_KEYS_DCP=y (W=1, zero warnings). No DCP hardware
available for runtime testing.
security/keys/trusted-keys/trusted_dcp.c | 15 +++++++++++----
1 file changed, 11 insertions(+), 4 deletions(-)
diff --git a/security/keys/trusted-keys/trusted_dcp.c
b/security/keys/trusted-keys/trusted_dcp.c
index 7b6eb655d..c078adebe 100644
--- a/security/keys/trusted-keys/trusted_dcp.c
+++ b/security/keys/trusted-keys/trusted_dcp.c
@@ -69,7 +69,7 @@ static bool skip_zk_test;
module_param_named(dcp_skip_zk_test, skip_zk_test, bool, 0);
MODULE_PARM_DESC(dcp_skip_zk_test, "Don't test whether device keys are
zero'ed");
-static unsigned int calc_blob_len(unsigned int payload_len)
+static size_t calc_blob_len(unsigned int payload_len)
{
return sizeof(struct dcp_blob_fmt) + payload_len + DCP_BLOB_AUTHLEN;
}
@@ -200,7 +200,8 @@ static int encrypt_blob_key(u8 *plain_key, u8
*encrypted_key)
static int trusted_dcp_seal(struct trusted_key_payload *p, char *datablob)
{
struct dcp_blob_fmt *b = (struct dcp_blob_fmt *)p->blob;
- int blen, ret;
+ size_t blen;
+ int ret;
u8 *plain_blob_key;
blen = calc_blob_len(p->key_len);
@@ -242,7 +243,8 @@ static int trusted_dcp_seal(struct trusted_key_payload *p,
char *datablob)
static int trusted_dcp_unseal(struct trusted_key_payload *p, char *datablob)
{
struct dcp_blob_fmt *b = (struct dcp_blob_fmt *)p->blob;
- int blen, ret;
+ size_t blen;
+ int ret;
u8 *plain_blob_key = NULL;
if (b->fmt_version != DCP_BLOB_VERSION) {
@@ -253,9 +255,14 @@ static int trusted_dcp_unseal(struct trusted_key_payload
*p, char *datablob)
}
p->key_len = le32_to_cpu(b->payload_len);
+ if (p->key_len < MIN_KEY_SIZE || p->key_len > MAX_KEY_SIZE) {
+ ret = -EINVAL;
+ goto out;
+ }
+
blen = calc_blob_len(p->key_len);
if (blen != p->blob_len) {
- pr_err("DCP blob has bad length: %i != %i\n", blen,
+ pr_err("DCP blob has bad length: %zu != %u\n", blen,
p->blob_len);
ret = -EINVAL;
goto out;
base-commit: 6d41c11ef3044788902a05e292cd7f0a9c7a8157
--
2.53.0
