Detect kernel version for dm-crypt kernel key bugfix.

When loading first dm-crypt table (or action that triggers dm-crypt
module load) we do not know dm-crypt version yet. Let's assume all
kernels before 4.15.0 are flawed and reject VK load via kernel keyring
service.

When dm-crypt is already in kernel, check for correct target version
instead (v1.18.1 or later).

lib/internal.h

@@ -197,4 +197,11 @@ int crypt_get_integrity_tag_size(struct crypt_device *cd);
 int crypt_key_in_keyring(struct crypt_device *cd);
 void crypt_set_key_in_keyring(struct crypt_device *cd, unsigned key_in_keyring);
 
+static inline uint64_t version(uint16_t major, uint16_t minor, uint16_t patch, uint16_t release)
+{
+	return (uint64_t)release | ((uint64_t)patch << 16) | ((uint64_t)minor << 32) | ((uint64_t)major << 48);
+}
+
+int kernel_version(uint64_t *kversion);
+
 #endif /* INTERNAL_H */

lib/setup.c

@@ -4101,6 +4101,15 @@ static int kernel_keyring_support(void)
 	return _kernel_keyring_supported;
 }
 
+static int dmcrypt_keyring_bug(void)
+{
+	uint64_t kversion;
+
+	if (kernel_version(&kversion))
+		return 1;
+	return kversion < version(4,15,0,0);
+}
+
 int crypt_use_keyring_for_vk(const struct crypt_device *cd)
 {
 	uint32_t dmc_flags;
@@ -4113,7 +4122,7 @@ int crypt_use_keyring_for_vk(const struct crypt_device *cd)
 		return 0;
 
 	if (dm_flags(DM_CRYPT, &dmc_flags))
-		return 1;
+		return dmcrypt_keyring_bug() ? 0 : 1;
 
 	return (dmc_flags & DM_KERNEL_KEYRING_SUPPORTED);
 }

lib/utils.c

@@ -30,6 +30,7 @@
 #include <sys/resource.h>
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <sys/utsname.h>
 
 #include "internal.h"
 
@@ -553,3 +554,27 @@ int crypt_keyfile_read(struct crypt_device *cd,  const char *keyfile,
 	return crypt_keyfile_device_read(cd, keyfile, key, key_size_read,
 					 keyfile_offset, keyfile_size_max, flags);
 }
+
+int kernel_version(uint64_t *kversion)
+{
+	struct utsname uts;
+	uint16_t maj, min, patch, rel;
+	int r = -EINVAL;
+
+	if (uname(&uts) < 0)
+		return r;
+
+	if (sscanf(uts.release, "%" SCNu16  ".%" SCNu16 ".%" SCNu16 "-%" SCNu16,
+		   &maj, &min, &patch, &rel) == 4)
+		r = 0;
+	else if (sscanf(uts.release,  "%" SCNu16 ".%" SCNu16 ".%" SCNu16,
+			&maj, &min, &patch) == 3) {
+		rel = 0;
+		r = 0;
+	}
+
+	if (!r)
+		*kversion = version(maj, min, patch, rel);
+
+	return r;
+}