bpf: refactor the BPF code and postpone querying of the engine mode

BPF codebase queried engine mode earlier than it was determined from
the configuration file/command line. As a result it used the default (IDS)
mode where it could've been configured later on to the IPS mode.
This could lead into an undefined behavior as some Suricata modules behave
according to the engine mode.

PF-Ring, Netmap and AF-Packet all shared almost identical code for
determining the engine mode. It was put into one common function.
Omitted the usage of SCStrdup function in PF-Ring module as it is
uppercased during thread initialization phase.

Ticket: #5958

src/runmode-af-packet.c

@@ -54,6 +54,7 @@
 #include "util-ioctl.h"
 #include "util-ebpf.h"
 #include "util-byte.h"
+#include "util-bpf.h"
 
 #include "source-af-packet.h"
 
@@ -118,7 +119,6 @@ static void *ParseAFPConfig(const char *iface)
     const char *copymodestr;
     intmax_t value;
     int boolval;
-    const char *bpf_filter = NULL;
     const char *out_iface = NULL;
     int cluster_type = PACKET_FANOUT_HASH;
     const char *ebpf_file = NULL;
@@ -157,14 +157,6 @@ static void *ParseAFPConfig(const char *iface)
     aconf->ebpf_t_config.cpus_count = UtilCpuGetNumProcessorsConfigured();
 #endif
 
-    if (ConfGet("bpf-filter", &bpf_filter) == 1) {
-        if (strlen(bpf_filter) > 0) {
-            aconf->bpf_filter = bpf_filter;
-            SCLogConfig("Going to use command-line provided bpf filter '%s'",
-                       aconf->bpf_filter);
-        }
-    }
-
     /* Find initial node */
     af_packet_node = ConfGetNode("af-packet");
     if (af_packet_node == NULL) {
@@ -370,16 +362,7 @@ static void *ParseAFPConfig(const char *iface)
                                        "tracking issues, use it at your own risk.");
     }
 
-    /*load af_packet bpf filter*/
-    /* command line value has precedence */
-    if (ConfGet("bpf-filter", &bpf_filter) != 1) {
-        if (ConfGetChildValueWithDefault(if_root, if_default, "bpf-filter", &bpf_filter) == 1) {
-            if (strlen(bpf_filter) > 0) {
-                aconf->bpf_filter = bpf_filter;
-                SCLogConfig("Going to use bpf filter %s", aconf->bpf_filter);
-            }
-        }
-    }
+    ConfSetBPFFilter(if_root, if_default, iface, &aconf->bpf_filter);
 
     if (ConfGetChildValueWithDefault(if_root, if_default, "ebpf-lb-file", &ebpf_file) != 1) {
         aconf->ebpf_lb_file = NULL;

src/runmode-netmap.c

@@ -52,6 +52,7 @@
 #include "util-runmodes.h"
 #include "util-ioctl.h"
 #include "util-byte.h"
+#include "util-bpf.h"
 
 #if HAVE_NETMAP
 #define NETMAP_WITH_LIBS
@@ -142,15 +143,6 @@ static int ParseNetmapSettings(NetmapIfaceSettings *ns, const char *iface,
         ns->real = true;
     }
 
-    const char *bpf_filter = NULL;
-    if (ConfGet("bpf-filter", &bpf_filter) == 1) {
-        if (strlen(bpf_filter) > 0) {
-            ns->bpf_filter = bpf_filter;
-            SCLogInfo("Going to use command-line provided bpf filter '%s'",
-                    ns->bpf_filter);
-        }
-    }
-
     if (if_root == NULL && if_default == NULL) {
         SCLogInfo("Unable to find netmap config for "
                 "interface \"%s\" or \"default\", using default values",
@@ -181,16 +173,7 @@ static int ParseNetmapSettings(NetmapIfaceSettings *ns, const char *iface,
         }
     }
 
-    /* load netmap bpf filter */
-    /* command line value has precedence */
-    if (ns->bpf_filter == NULL) {
-        if (ConfGetChildValueWithDefault(if_root, if_default, "bpf-filter", &bpf_filter) == 1) {
-            if (strlen(bpf_filter) > 0) {
-                ns->bpf_filter = bpf_filter;
-                SCLogInfo("Going to use bpf filter %s", ns->bpf_filter);
-            }
-        }
-    }
+    ConfSetBPFFilter(if_root, if_default, iface, &ns->bpf_filter);
 
     int boolval = 0;
     (void)ConfGetChildValueBoolWithDefault(if_root, if_default, "disable-promisc", (int *)&boolval);

src/runmode-pfring.c

@@ -23,6 +23,7 @@
 #include "source-pfring.h"
 #include "output.h"
 
+#include "util-bpf.h"
 #include "util-debug.h"
 #include "util-time.h"
 #include "util-cpu.h"
@@ -72,9 +73,6 @@ static void PfringDerefConfig(void *conf)
 {
     PfringIfaceConfig *pfp = (PfringIfaceConfig *)conf;
     if (SC_ATOMIC_SUB(pfp->ref, 1) == 1) {
-        if (pfp->bpf_filter) {
-            SCFree(pfp->bpf_filter);
-        }
         SCFree(pfp);
     }
 }
@@ -204,7 +202,6 @@ static void *ParsePfringConfig(const char *iface)
     const char *tmpctype = NULL;
     cluster_type default_ctype = CLUSTER_ROUND_ROBIN;
     int getctype = 0;
-    const char *bpf_filter = NULL;
     int bool_val;
 
     if (unlikely(pfconf == NULL)) {
@@ -313,32 +310,11 @@ static void *ParsePfringConfig(const char *iface)
         }
     }
 
-    /*load pfring bpf filter*/
-    /* command line value has precedence */
-    if (ConfGet("bpf-filter", &bpf_filter) == 1) {
-        if (strlen(bpf_filter) > 0) {
-            pfconf->bpf_filter = SCStrdup(bpf_filter);
-            if (unlikely(pfconf->bpf_filter == NULL)) {
-                SCLogError(SC_ERR_MEM_ALLOC,
-                           "Can't allocate BPF filter string");
-            } else {
-                SCLogDebug("Going to use command-line provided bpf filter %s",
-                           pfconf->bpf_filter);
-            }
-        }
-    } else {
-        if (ConfGetChildValueWithDefault(if_root, if_default, "bpf-filter", &bpf_filter) == 1) {
-            if (strlen(bpf_filter) > 0) {
-                pfconf->bpf_filter = SCStrdup(bpf_filter);
-                if (unlikely(pfconf->bpf_filter == NULL)) {
-                    SCLogError(SC_ERR_MEM_ALLOC,
-                               "Can't allocate BPF filter string");
-                } else {
-                    SCLogDebug("Going to use bpf filter %s",
-                               pfconf->bpf_filter);
-                }
-            }
-        }
+    ConfSetBPFFilter(if_root, if_default, pfconf->iface, &pfconf->bpf_filter);
+
+    if (pfconf->bpf_filter != NULL && EngineModeIsIPS()) {
+        FatalError(SC_ERR_NOT_SUPPORTED,
+                "BPF filter not available in IPS mode. Use firewall filtering if possible.");
     }
 
     if (ConfGet("pfring.cluster-type", &tmpctype) == 1) {

src/source-pfring.h

@@ -44,7 +44,7 @@ typedef struct PfringIfaceConfig_
     /* number of threads */
     int threads;
 
-    char *bpf_filter;
+    const char *bpf_filter;
 
     ChecksumValidationMode checksum_mode;
     SC_ATOMIC_DECLARE(unsigned int, ref);

src/suricata.c

@@ -471,16 +471,9 @@ static int SetBpfString(int argc, char *argv[])
     if (bpf_len == 0)
         return TM_ECODE_OK;
 
-    if (EngineModeIsIPS()) {
-        SCLogError(SC_ERR_NOT_SUPPORTED,
-                   "BPF filter not available in IPS mode."
-                   " Use firewall filtering if possible.");
-        return TM_ECODE_FAILED;
-    }
-
     bpf_filter = SCMalloc(bpf_len);
     if (unlikely(bpf_filter == NULL))
-        return TM_ECODE_OK;
+        return TM_ECODE_FAILED;
     memset(bpf_filter, 0x00, bpf_len);
 
     tmpindex = optind;

src/util-bpf.c

@@ -25,6 +25,31 @@
 #include "suricata-common.h"
 #include "suricata.h"
 #include "util-bpf.h"
+#include "conf.h"
+#include "util-debug.h"
+
+void ConfSetBPFFilter(
+        ConfNode *if_root, ConfNode *if_default, const char *iface, const char **bpf_filter)
+{
+    if (*bpf_filter != NULL) {
+        SCLogInfo("BPF filter already configured");
+        return;
+    }
+
+    /* command line value has precedence */
+    if (ConfGet("bpf-filter", bpf_filter) == 1) {
+        if (strlen(*bpf_filter) > 0) {
+            SCLogConfig("%s: using command-line provided bpf filter '%s'", iface, *bpf_filter);
+        }
+    } else if (ConfGetChildValueWithDefault(if_root, if_default, "bpf-filter", bpf_filter) ==
+               1) { // reading from a file
+        if (strlen(*bpf_filter) > 0) {
+            SCLogConfig("%s: using file provided bpf filter %s", iface, *bpf_filter);
+        }
+    } else {
+        SCLogDebug("No BPF filter found, skipping");
+    }
+}
 
 #if !defined __OpenBSD__
 

src/util-bpf.h

@@ -24,6 +24,11 @@
 #ifndef __UTIL_BPF_H__
 #define __UTIL_BPF_H__
 
+#include "conf.h"
+
+void ConfSetBPFFilter(
+        ConfNode *if_root, ConfNode *if_default, const char *iface, const char **bpf_filter);
+
 #if !defined __OpenBSD__
 
 int SCBPFCompile(int snaplen_arg, int linktype_arg, struct bpf_program *program,