selftests/bpf: Extend crypto_sanity selftest with invalid dst buffer

Small cleanup and test extension to probe the bpf_crypto_{encrypt,decrypt}()
kfunc when a bad dst buffer is passed in to assert that an error is returned.

Also, encrypt_sanity() and skb_crypto_setup() were explicit to set the global
status variable to zero before any test, so do the same for decrypt_sanity().
Do not explicitly zero the on-stack err before bpf_crypto_ctx_create() given
the kfunc is expected to do it internally for the success case.

Before kernel fix:

  # ./vmtest.sh -- ./test_progs -t crypto
  [...]
  [    1.531200] bpf_testmod: loading out-of-tree module taints kernel.
  [    1.533388] bpf_testmod: module verification failed: signature and/or required key missing - tainting kernel
  #87/1    crypto_basic/crypto_release:OK
  #87/2    crypto_basic/crypto_acquire:OK
  #87      crypto_basic:OK
  test_crypto_sanity:PASS:skel open 0 nsec
  test_crypto_sanity:PASS:ip netns add crypto_sanity_ns 0 nsec
  test_crypto_sanity:PASS:ip -net crypto_sanity_ns -6 addr add face::1/128 dev lo nodad 0 nsec
  test_crypto_sanity:PASS:ip -net crypto_sanity_ns link set dev lo up 0 nsec
  test_crypto_sanity:PASS:open_netns 0 nsec
  test_crypto_sanity:PASS:AF_ALG init fail 0 nsec
  test_crypto_sanity:PASS:if_nametoindex lo 0 nsec
  test_crypto_sanity:PASS:skb_crypto_setup fd 0 nsec
  test_crypto_sanity:PASS:skb_crypto_setup 0 nsec
  test_crypto_sanity:PASS:skb_crypto_setup retval 0 nsec
  test_crypto_sanity:PASS:skb_crypto_setup status 0 nsec
  test_crypto_sanity:PASS:create qdisc hook 0 nsec
  test_crypto_sanity:PASS:make_sockaddr 0 nsec
  test_crypto_sanity:PASS:attach encrypt filter 0 nsec
  test_crypto_sanity:PASS:encrypt socket 0 nsec
  test_crypto_sanity:PASS:encrypt send 0 nsec
  test_crypto_sanity:FAIL:encrypt status unexpected error: -5 (errno 95)
  #88      crypto_sanity:FAIL
  Summary: 1/2 PASSED, 0 SKIPPED, 1 FAILED

After kernel fix:

  # ./vmtest.sh -- ./test_progs -t crypto
  [...]
  [    1.540963] bpf_testmod: loading out-of-tree module taints kernel.
  [    1.542404] bpf_testmod: module verification failed: signature and/or required key missing - tainting kernel
  #87/1    crypto_basic/crypto_release:OK
  #87/2    crypto_basic/crypto_acquire:OK
  #87      crypto_basic:OK
  #88      crypto_sanity:OK
  Summary: 2/2 PASSED, 0 SKIPPED, 0 FAILED

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Cc: Vadim Fedorenko <vadim.fedorenko@linux.dev>

Author: borkmann

tools/testing/selftests/bpf/progs/crypto_sanity.c

@@ -14,7 +14,7 @@ unsigned char key[256] = {};
 u16 udp_test_port = 7777;
 u32 authsize, key_len;
 char algo[128] = {};
-char dst[16] = {};
+char dst[16] = {}, dst_bad[8] = {};
 int status;
 
 static int skb_dynptr_validate(struct __sk_buff *skb, struct bpf_dynptr *psrc)
@@ -59,19 +59,18 @@ int skb_crypto_setup(void *ctx)
 		.authsize = authsize,
 	};
 	struct bpf_crypto_ctx *cctx;
-	int err = 0;
+	int err;
 
 	status = 0;
-
 	if (key_len > 256) {
 		status = -EINVAL;
 		return 0;
 	}
 
 	__builtin_memcpy(&params.algo, algo, sizeof(algo));
 	__builtin_memcpy(&params.key, key, sizeof(key));
-	cctx = bpf_crypto_ctx_create(&params, sizeof(params), &err);
 
+	cctx = bpf_crypto_ctx_create(&params, sizeof(params), &err);
 	if (!cctx) {
 		status = err;
 		return 0;
@@ -80,7 +79,6 @@ int skb_crypto_setup(void *ctx)
 	err = crypto_ctx_insert(cctx);
 	if (err && err != -EEXIST)
 		status = err;
-
 	return 0;
 }
 
@@ -92,6 +90,7 @@ int decrypt_sanity(struct __sk_buff *skb)
 	struct bpf_dynptr psrc, pdst;
 	int err;
 
+	status = 0;
 	err = skb_dynptr_validate(skb, &psrc);
 	if (err < 0) {
 		status = err;
@@ -110,13 +109,23 @@ int decrypt_sanity(struct __sk_buff *skb)
 		return TC_ACT_SHOT;
 	}
 
-	/* dst is a global variable to make testing part easier to check. In real
-	 * production code, a percpu map should be used to store the result.
+	/* Check also bad case where the dst buffer is smaller than the
+	 * skb's linear section.
+	 */
+	bpf_dynptr_from_mem(dst_bad, sizeof(dst_bad), 0, &pdst);
+	status = bpf_crypto_decrypt(ctx, &psrc, &pdst, NULL);
+	if (!status)
+		status = -EIO;
+	if (status != -EINVAL)
+		goto err;
+
+	/* dst is a global variable to make testing part easier to check.
+	 * In real production code, a percpu map should be used to store
+	 * the result.
 	 */
 	bpf_dynptr_from_mem(dst, sizeof(dst), 0, &pdst);
-
 	status = bpf_crypto_decrypt(ctx, &psrc, &pdst, NULL);
-
+err:
 	return TC_ACT_SHOT;
 }
 
@@ -129,7 +138,6 @@ int encrypt_sanity(struct __sk_buff *skb)
 	int err;
 
 	status = 0;
-
 	err = skb_dynptr_validate(skb, &psrc);
 	if (err < 0) {
 		status = err;
@@ -148,13 +156,23 @@ int encrypt_sanity(struct __sk_buff *skb)
 		return TC_ACT_SHOT;
 	}
 
-	/* dst is a global variable to make testing part easier to check. In real
-	 * production code, a percpu map should be used to store the result.
+	/* Check also bad case where the dst buffer is smaller than the
+	 * skb's linear section.
+	 */
+	bpf_dynptr_from_mem(dst_bad, sizeof(dst_bad), 0, &pdst);
+	status = bpf_crypto_encrypt(ctx, &psrc, &pdst, NULL);
+	if (!status)
+		status = -EIO;
+	if (status != -EINVAL)
+		goto err;
+
+	/* dst is a global variable to make testing part easier to check.
+	 * In real production code, a percpu map should be used to store
+	 * the result.
 	 */
 	bpf_dynptr_from_mem(dst, sizeof(dst), 0, &pdst);
-
 	status = bpf_crypto_encrypt(ctx, &psrc, &pdst, NULL);
-
+err:
 	return TC_ACT_SHOT;
 }