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#define _GNU_SOURCE
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/fanotify.h>
#include "json.h"
#include "error.h"
#include "output.h"
#include "fanotify.h"
#include "hash_ledger.h"
#include "time_common.h"
// set up fanotify descriptor. returns initialized descriptor on
// success, -1 on error
int setup_fanotify(void) {
int fan_fd = fanotify_init(FAN_CLASS_PRE_CONTENT | FAN_CLOEXEC | FAN_NONBLOCK,
O_RDONLY | O_CLOEXEC | O_LARGEFILE);
if (fan_fd < 0) {
error("fanotify_init failed: %s", strerror(errno));
return -1;
}
// TODO mark all mount points instead of /
if (fanotify_mark(fan_fd,
FAN_MARK_ADD | FAN_MARK_MOUNT,
FAN_OPEN_EXEC | FAN_OPEN_EXEC_PERM,
AT_FDCWD,
"/") < 0) {
error("fanotify_mark failed: %s", strerror(errno));
close(fan_fd);
return -1;
}
// set non-blocking
int flags = fcntl(fan_fd, F_GETFL, 0);
fcntl(fan_fd, F_SETFL, flags | O_NONBLOCK);
return fan_fd;
}
typedef struct {
struct hash_entry *entry;
pattern_table_t *patterns;
size_t match_count;
} match_context_t;
static void match_callback(const struct ac_match *m, void *user_data) {
match_context_t *ctx = user_data;
//printf("fanotify matched: %s at offset %zu\n", m->id, m->offset);
if (ctx->entry->matched_pattern_count < MAX_MATCHED_PATTERNS) {
ctx->entry->matched_patterns[ctx->entry->matched_pattern_count++] = m->id;
}
pattern_t *p = pattern_table_find(ctx->patterns, m->id);
if (p && p->match_count < MAX_MATCHED_PATTERNS) {
p->match_offsets[p->match_count++] = m->offset;
}
}
// TODO handle old style FID-based events as well as old style FD
// TODO hash-based allow and blocklists
void select_fanotify(int fan_fd, agent_context_t *ctx) {
struct fanotify_event_metadata buf[4096];
ssize_t len = read(fan_fd, buf, sizeof(buf));
if (len < 0) {
if (errno != EAGAIN) {
error("fanotify read: %s", strerror(errno));
}
return;
}
struct fanotify_event_metadata *metadata;
for (metadata = buf; FAN_EVENT_OK(metadata, len); metadata = FAN_EVENT_NEXT(metadata, len)) {
if (metadata->mask & FAN_OPEN_EXEC_PERM) {
struct fanotify_response response;
response.fd = metadata->fd;
response.response = FAN_ALLOW;
char path[PATH_MAX];
snprintf(path, sizeof(path), "/proc/self/fd/%d", metadata->fd);
char target[PATH_MAX];
ssize_t len = readlink(path, target, sizeof(target) - 1);
if (len >= 0) {
target[len] = '\0';
} else {
error("readlink: %s", strerror(errno));
}
// hash_ledger_find(ctx->hash_ledger, target)
// - if not in ledger, create and scan.
// - if in ledger
// - scan if too much time passed, scan again
// - if verdict is block, send FAN_DENY and emit log w/ rule matches
// - if verdict is quarantine, block and quarantine
// = if verdict is allow, allow it.
struct hash_entry *he = hash_ledger_find(ctx->hash_ledger, target);
if (!he) {
struct stat sb;
stat(target, &sb);
he = hash_ledger_add_or_update(ctx->hash_ledger, target, &sb);
}
scan_verdict_t verdict = VERDICT_INFORMATIONAL;
if (he->last_scanned == 0 || time(NULL) - he->last_scanned > 600) {
match_context_t mctx = {
.entry = he,
.patterns = &ctx->rules.patterns,
.match_count = 0
};
for (size_t i = 0; i < ctx->rules.patterns.count; i++) {
ctx->rules.patterns.patterns[i].match_count = 0;
}
pattern_table_clear_matches(&ctx->rules.patterns);
ac_match_path(ctx->ac, target, match_callback, &mctx);
//ac_match_fd(ctx->ac, metadata->fd, match_callback, &mctx);
he->matched_rule_count = 0;
he->matched_pattern_count = 0;
for (size_t i = 0; i < ctx->rules.rule_count; i++) {
const rule_t *r = &ctx->rules.rules[i];
if (evaluate_rule(r, &ctx->rules.patterns)) {
//printf("fanotify match: %s\n", r->id);
if (he->matched_rule_count < MAX_MATCHED_RULES) {
he->matched_rules[he->matched_rule_count++] = r->id;
}
if (r->action == RULE_BLOCK) {
verdict = VERDICT_BLOCK;
break;
} else if (r->action == RULE_QUARANTINE && verdict < VERDICT_QUARANTINE) {
verdict = VERDICT_QUARANTINE;
} else if (r->action == RULE_ALLOW && verdict < VERDICT_ALLOW) {
verdict = VERDICT_ALLOW;
}
}
}
he->verdict = verdict;
he->last_scanned = time(NULL);
he->scan_count++;
}
switch (he->verdict) {
case VERDICT_BLOCK:
case VERDICT_QUARANTINE:
response.response = FAN_DENY; // deny blocked/quarantined files.
break;
default:
response.response = FAN_ALLOW; // fail open
break;
}
// TODO emit log for rule matches w/ allow action, not only block/quarantine
if (response.response == FAN_DENY) {
json_t buf = {0};
json_init(&buf);
json_start_object(&buf);
json_add_double(&buf, "timestamp", timestamp());
json_add_string(&buf, "hostname", ctx->hostname);
json_add_string(&buf, "event_type", "fanotify_block");
json_add_string(&buf, "verdict",
he->verdict == VERDICT_BLOCK ? "block" :
he->verdict == VERDICT_QUARANTINE ? "quarantine" :
he->verdict == VERDICT_ALLOW ? "allow" : "informational");
// TODO filesize
json_add_string(&buf, "md5", he->md5);
json_add_string(&buf, "sha256", he->sha256);
json_add_double(&buf, "entropy", he->entropy);
json_add_array_start(&buf, "matched_rules");
for (size_t i = 0; i < he->matched_rule_count; i++) {
json_array_add_string(&buf, he->matched_rules[i]);
}
json_end_array(&buf);
json_end_object(&buf);
output(json_get(&buf));
json_free(&buf);
}
//printf("\n\n\nfanotify: fd: %d, pid: %d, mask: %lld, target: %s (%s) verdict: %d\n\n\n", metadata->fd, metadata->pid, metadata->mask, target, he->md5, he->verdict);
if (write(fan_fd, &response, sizeof(response)) < 0) {
error("fanotify write response: %s", strerror(errno));
}
} else if (metadata->mask & FAN_OPEN_EXEC) {
// TODO separate branch for FAN_OPEN_EXEC if PERM isn't
// available--prefer this over proc_connector EXEC events
}
if (metadata->fd >= 0) {
close(metadata->fd);
}
}
}
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