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tls: openssl: Fail verification if client certificate is not provided #11254

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tls: openssl: Fail verification if client certificate is not provided #11254

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4cf27c6
tls: openssl: Fail verification if client certificate is not provided
edbingo Dec 4, 2025
3a400f1
Merge branch 'fluent:master' into master
edbingo Dec 15, 2025
d86276d
tls: introduce new option for strict client verification
edbingo Dec 15, 2025
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1 change: 1 addition & 0 deletions include/fluent-bit/flb_input.h
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Original file line number Diff line number Diff line change
Expand Up @@ -446,6 +446,7 @@ struct flb_input_instance {
/* TLS settings */
int use_tls; /* bool, try to use TLS for I/O */
int tls_verify; /* Verify certs (default: true) */
int tls_verify_client; /* Verify client certs (default: false) */
int tls_verify_hostname; /* Verify hostname (default: false) */
int tls_debug; /* mbedtls debug level */
char *tls_vhost; /* Virtual hostname for SNI */
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3 changes: 3 additions & 0 deletions include/fluent-bit/tls/flb_tls.h
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Expand Up @@ -76,6 +76,7 @@ struct flb_tls_backend {

/* Additional settings */
int (*context_alpn_set) (void *, const char *);
int (*context_set_verify_client) (void *, int);

/* TLS Protocol version */
int (*set_minmax_proto) (struct flb_tls *tls, const char *, const char *);
Expand Down Expand Up @@ -104,6 +105,7 @@ struct flb_tls_backend {
/* Main TLS context */
struct flb_tls {
int verify; /* FLB_TRUE | FLB_FALSE */
int verify_client; /* Verify client certificate */
int debug; /* Debug level */
char *vhost; /* Virtual hostname for SNI */
int mode; /* Client or Server */
Expand Down Expand Up @@ -131,6 +133,7 @@ struct flb_tls *flb_tls_create(int mode,
int flb_tls_destroy(struct flb_tls *tls);

int flb_tls_set_alpn(struct flb_tls *tls, const char *alpn);
int flb_tls_set_verify_client(struct flb_tls *tls, int verify_client);

int flb_tls_set_verify_hostname(struct flb_tls *tls, int verify_hostname);
#if defined(FLB_SYSTEM_WINDOWS)
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15 changes: 15 additions & 0 deletions src/flb_input.c
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Expand Up @@ -398,6 +398,7 @@ struct flb_input_instance *flb_input_new(struct flb_config *config,
instance->tls = NULL;
instance->tls_debug = -1;
instance->tls_verify = FLB_TRUE;
instance->tls_verify_client = FLB_FALSE;
instance->tls_verify_hostname = FLB_FALSE;
instance->tls_vhost = NULL;
instance->tls_ca_path = NULL;
Expand Down Expand Up @@ -651,6 +652,10 @@ int flb_input_set_property(struct flb_input_instance *ins,
ins->tls_verify = flb_utils_bool(tmp);
flb_sds_destroy(tmp);
}
else if (prop_key_check("tls.verify_client_cert", k, len) == 0 && tmp) {
ins->tls_verify_client = flb_utils_bool(tmp);
flb_sds_destroy(tmp);
}
else if (prop_key_check("tls.verify_hostname", k, len) == 0 && tmp) {
ins->tls_verify_hostname = flb_utils_bool(tmp);
flb_sds_destroy(tmp);
Expand Down Expand Up @@ -1331,6 +1336,16 @@ int flb_input_instance_init(struct flb_input_instance *ins,
return -1;
}
}

if (ins->tls_verify_client == FLB_TRUE) {
ret = flb_tls_set_verify_client(ins->tls, ins->tls_verify_client);
if (ret == -1) {
flb_error("[input %s] error set up to verify client certificate in TLS context",
ins->name);

return -1;
}
}
}

struct flb_config_map *m;
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20 changes: 20 additions & 0 deletions src/tls/flb_tls.c
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Expand Up @@ -35,6 +35,11 @@ struct flb_config_map tls_configmap[] = {
0, FLB_FALSE, 0,
"Force certificate validation",
},
{
FLB_CONFIG_MAP_BOOL, "tls.verify_client_cert", "off",
0, FLB_FALSE, 0,
"Enable or disable client certificate verification",
},
{
FLB_CONFIG_MAP_INT, "tls.debug", "1",
0, FLB_FALSE, 0,
Expand Down Expand Up @@ -285,6 +290,21 @@ int flb_tls_set_alpn(struct flb_tls *tls, const char *alpn)
return 0;
}

int flb_tls_set_verify_client(struct flb_tls *tls, int verify_client)
{
if (!tls) {
return -1;
}

tls->verify_client = verify_client;

if (tls->ctx && tls->api->context_set_verify_client) {
return tls->api->context_set_verify_client(tls->ctx, verify_client);
}

return 0;
}

int flb_tls_set_verify_hostname(struct flb_tls *tls, int verify_hostname)
{
if (!tls) {
Expand Down
18 changes: 17 additions & 1 deletion src/tls/openssl.c
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Original file line number Diff line number Diff line change
Expand Up @@ -301,6 +301,20 @@ int tls_context_alpn_set(void *ctx_backend, const char *alpn)
return result;
}

static int tls_context_set_verify_client(void *ctx_backend, int verify_client)
{
struct tls_context *ctx = ctx_backend;
int mode;

if (ctx->mode == FLB_TLS_SERVER_MODE && verify_client == FLB_TRUE) {
mode = SSL_CTX_get_verify_mode(ctx->ctx);
mode |= SSL_VERIFY_FAIL_IF_NO_PEER_CERT;
SSL_CTX_set_verify(ctx->ctx, mode, NULL);
}

return 0;
}

#ifdef _MSC_VER
/* Parse certstore_name prefix like
*
Expand Down Expand Up @@ -801,7 +815,8 @@ static void *tls_context_create(int verify,
SSL_CTX_set_verify(ssl_ctx, SSL_VERIFY_NONE, NULL);
}
else {
SSL_CTX_set_verify(ssl_ctx, SSL_VERIFY_PEER, NULL);
int verify_flags = SSL_VERIFY_PEER;
SSL_CTX_set_verify(ssl_ctx, verify_flags, NULL);
}

/* ca_path | ca_file */
Expand Down Expand Up @@ -1574,6 +1589,7 @@ static struct flb_tls_backend tls_openssl = {
.context_create = tls_context_create,
.context_destroy = tls_context_destroy,
.context_alpn_set = tls_context_alpn_set,
.context_set_verify_client = tls_context_set_verify_client,
.session_alpn_get = tls_session_alpn_get,
.set_minmax_proto = tls_set_minmax_proto,
.set_ciphers = tls_set_ciphers,
Expand Down