bpf_crypto_ctx_create() validates the overall size of
struct bpf_crypto_params, but it does not verify that the fixed-width
type[14] and algo[128] fields are NUL-terminated before passing them to
string consumers.

A caller can therefore fill either field without a terminator and cause
bpf_crypto_get_type(), has_algo(), or alloc_tfm() to read past the end
of the fixed buffer.

Reject parameter blocks whose type or algorithm name does not contain a
terminating NUL within the advertised field width.

Fixes: 3e1c6f35409f ("bpf: make common crypto API for TC/XDP programs")
Cc: stable@vger.kernel.org

Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
---
 kernel/bpf/crypto.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kernel/bpf/crypto.c b/kernel/bpf/crypto.c
index 51f89cecefb4..8732689803a6 100644
--- a/kernel/bpf/crypto.c
+++ b/kernel/bpf/crypto.c
@@ -155,6 +155,12 @@ bpf_crypto_ctx_create(const struct bpf_crypto_params *params, u32 params__sz,
 		return NULL;
 	}
 
+	if (strnlen(params->type, sizeof(params->type)) == sizeof(params->type) ||
+	    strnlen(params->algo, sizeof(params->algo)) == sizeof(params->algo)) {
+		*err = -EINVAL;
+		return NULL;
+	}
+
 	type = bpf_crypto_get_type(params->type);
 	if (IS_ERR(type)) {
 		*err = PTR_ERR(type);
-- 
2.50.1 (Apple Git-155)

On 17.04.2026 08:31, Pengpeng Hou wrote:
> bpf_crypto_ctx_create() validates the overall size of
> struct bpf_crypto_params, but it does not verify that the fixed-width
> type[14] and algo[128] fields are NUL-terminated before passing them to
> string consumers.
> 
> A caller can therefore fill either field without a terminator and cause
> bpf_crypto_get_type(), has_algo(), or alloc_tfm() to read past the end
> of the fixed buffer.
How can this happen for static defined type/algo structures?

bpf_crypto_ctx_create() receives a BPF-supplied params pointer. The
current selftests use static initializers, but BPF programs can also
build the struct in writable BPF memory before calling the kfunc. The
verifier checks that the memory is accessible; it does not prove that
the fixed type[] and algo[] fields are NUL-terminated strings.

Copy the params once into a local snapshot, validate the reserved fields
and fixed-width strings there, and then use the same snapshot for all
later checks and crypto API calls. This also keeps key_len and authsize
stable across validation and use if params points at mutable BPF memory.

Add a selftest that fills algo[] completely and expects -EINVAL.

Fixes: 3e1c6f35409f ("bpf: make common crypto API for TC/XDP programs")
Signed-off-by: Pengpeng Hou <pengpeng@iscas.ac.cn>
---
Changes since v1:
- copy struct bpf_crypto_params into a local snapshot before validation
- use the snapshot for all string, key_len and authsize checks and uses
- add a BPF selftest for an unterminated algorithm name

diff --git a/kernel/bpf/crypto.c b/kernel/bpf/crypto.c
index 51f89cecefb4..e2dc3dfb4d85 100644
--- a/kernel/bpf/crypto.c
+++ b/kernel/bpf/crypto.c
@@ -147,31 +147,46 @@ bpf_crypto_ctx_create(const struct bpf_crypto_params *params, u32 params__sz,
 		      int *err)
 {
 	const struct bpf_crypto_type *type;
+	struct bpf_crypto_params params_copy;
 	struct bpf_crypto_ctx *ctx;
 
-	if (!params || params->reserved[0] || params->reserved[1] ||
-	    params__sz != sizeof(struct bpf_crypto_params)) {
+	if (!params || params__sz != sizeof(params_copy)) {
 		*err = -EINVAL;
 		return NULL;
 	}
 
-	type = bpf_crypto_get_type(params->type);
+	params_copy = *params;
+
+	if (params_copy.reserved[0] || params_copy.reserved[1]) {
+		*err = -EINVAL;
+		return NULL;
+	}
+
+	if (strnlen(params_copy.type, sizeof(params_copy.type)) ==
+	    sizeof(params_copy.type) ||
+	    strnlen(params_copy.algo, sizeof(params_copy.algo)) ==
+	    sizeof(params_copy.algo)) {
+		*err = -EINVAL;
+		return NULL;
+	}
+
+	type = bpf_crypto_get_type(params_copy.type);
 	if (IS_ERR(type)) {
 		*err = PTR_ERR(type);
 		return NULL;
 	}
 
-	if (!type->has_algo(params->algo)) {
+	if (!type->has_algo(params_copy.algo)) {
 		*err = -EOPNOTSUPP;
 		goto err_module_put;
 	}
 
-	if (!!params->authsize ^ !!type->setauthsize) {
+	if (!!params_copy.authsize ^ !!type->setauthsize) {
 		*err = -EOPNOTSUPP;
 		goto err_module_put;
 	}
 
-	if (!params->key_len || params->key_len > sizeof(params->key)) {
+	if (!params_copy.key_len || params_copy.key_len > sizeof(params_copy.key)) {
 		*err = -EINVAL;
 		goto err_module_put;
 	}
@@ -183,19 +198,19 @@ bpf_crypto_ctx_create(const struct bpf_crypto_params *params, u32 params__sz,
 	}
 
 	ctx->type = type;
-	ctx->tfm = type->alloc_tfm(params->algo);
+	ctx->tfm = type->alloc_tfm(params_copy.algo);
 	if (IS_ERR(ctx->tfm)) {
 		*err = PTR_ERR(ctx->tfm);
 		goto err_free_ctx;
 	}
 
-	if (params->authsize) {
-		*err = type->setauthsize(ctx->tfm, params->authsize);
+	if (params_copy.authsize) {
+		*err = type->setauthsize(ctx->tfm, params_copy.authsize);
 		if (*err)
 			goto err_free_tfm;
 	}
 
-	*err = type->setkey(ctx->tfm, params->key, params->key_len);
+	*err = type->setkey(ctx->tfm, params_copy.key, params_copy.key_len);
 	if (*err)
 		goto err_free_tfm;
 
diff --git a/tools/testing/selftests/bpf/prog_tests/crypto_sanity.c b/tools/testing/selftests/bpf/prog_tests/crypto_sanity.c
index 42bd07f7218d..044711e7263a 100644
--- a/tools/testing/selftests/bpf/prog_tests/crypto_sanity.c
+++ b/tools/testing/selftests/bpf/prog_tests/crypto_sanity.c
@@ -117,6 +117,19 @@ void test_crypto_sanity(void)
 	udp_test_port = skel->data->udp_test_port;
 	memcpy(skel->bss->key, crypto_key, sizeof(crypto_key));
 	snprintf(skel->bss->algo, 128, "%s", algo);
+
+	pfd = bpf_program__fd(skel->progs.skb_crypto_setup_bad_algo);
+	if (!ASSERT_GT(pfd, 0, "skb_crypto_setup_bad_algo fd"))
+		goto fail;
+
+	err = bpf_prog_test_run_opts(pfd, &opts);
+	if (!ASSERT_OK(err, "skb_crypto_setup_bad_algo") ||
+	    !ASSERT_OK(opts.retval, "skb_crypto_setup_bad_algo retval"))
+		goto fail;
+
+	if (!ASSERT_OK(skel->bss->status, "skb_crypto_setup_bad_algo status"))
+		goto fail;
+
 	pfd = bpf_program__fd(skel->progs.skb_crypto_setup);
 	if (!ASSERT_GT(pfd, 0, "skb_crypto_setup fd"))
 		goto fail;
diff --git a/tools/testing/selftests/bpf/progs/crypto_sanity.c b/tools/testing/selftests/bpf/progs/crypto_sanity.c
index dfd8a258f14a..32977b797042 100644
--- a/tools/testing/selftests/bpf/progs/crypto_sanity.c
+++ b/tools/testing/selftests/bpf/progs/crypto_sanity.c
@@ -82,6 +82,34 @@ int skb_crypto_setup(void *ctx)
 	return 0;
 }
 
+SEC("syscall")
+int skb_crypto_setup_bad_algo(void *ctx)
+{
+	struct bpf_crypto_params params = {
+		.type = "skcipher",
+		.key_len = 16,
+	};
+	struct bpf_crypto_ctx *cctx;
+	int err = 0;
+
+	status = 0;
+
+	__builtin_memset(params.algo, 'a', sizeof(params.algo));
+	__builtin_memcpy(&params.key, key, sizeof(key));
+
+	cctx = bpf_crypto_ctx_create(&params, sizeof(params), &err);
+	if (cctx) {
+		bpf_crypto_ctx_release(cctx);
+		status = -EIO;
+		return 0;
+	}
+
+	if (err != -EINVAL)
+		status = err;
+
+	return 0;
+}
+
 SEC("tc")
 int decrypt_sanity(struct __sk_buff *skb)
 {
-- 
2.50.1 (Apple Git-155)