libbpf-tools: Fix misaligned pointer accesses in tcptracer

The perf buffer in tcptracer doesn't maintain 8 byte alignment
for saddr_v4, daddr_v4 and ts_us in struct event.
When building with "-fsanitize=alignment -fsanitize-trap=undefined"
failures happen in handle_event. Fix these by copying the event
from the perf buffer before accessing.

This is similar to a fix in exitsnoop where different ways to handle
misaligned pointers were discussed:
iovisor#4760

Signed-off-by: Ian Rogers <[email protected]>

libbpf-tools/tcptracer.c

@@ -167,7 +167,7 @@ static void print_events_header()
 
 static void handle_event(void *ctx, int cpu, void *data, __u32 data_sz)
 {
- const struct event *event = data;
+ struct event event;
  char src[INET6_ADDRSTRLEN];
  char dst[INET6_ADDRSTRLEN];
  union {
@@ -176,28 +176,35 @@ static void handle_event(void *ctx, int cpu, void *data, __u32 data_sz)
  } s, d;
  static __u64 start_ts;
 
- if (event->af == AF_INET) {
- s.x4.s_addr = event->saddr_v4;
- d.x4.s_addr = event->daddr_v4;
- } else if (event->af == AF_INET6) {
- memcpy(&s.x6.s6_addr, &event->saddr_v6, sizeof(s.x6.s6_addr));
- memcpy(&d.x6.s6_addr, &event->daddr_v6, sizeof(d.x6.s6_addr));
+ if (data_sz < sizeof(event)) {
+ printf("Error: packet too small\n");
+ return;
+ }
+ /* Copy data as alignment in the perf buffer isn't guaranteed. */
+ memcpy(&event, data, sizeof(event));
+
+ if (event.af == AF_INET) {
+ s.x4.s_addr = event.saddr_v4;
+ d.x4.s_addr = event.daddr_v4;
+ } else if (event.af == AF_INET6) {
+ memcpy(&s.x6.s6_addr, &event.saddr_v6, sizeof(s.x6.s6_addr));
+ memcpy(&d.x6.s6_addr, &event.daddr_v6, sizeof(d.x6.s6_addr));
  } else {
- warn("broken event: event->af=%d", event->af);
+ warn("broken event: event.af=%d", event.af);
  return;
  }
 
  if (env.print_timestamp) {
  if (start_ts == 0)
- start_ts = event->ts_us;
- printf("%-9.3f", (event->ts_us - start_ts) / 1000000.0);
+ start_ts = event.ts_us;
+ printf("%-9.3f", (event.ts_us - start_ts) / 1000000.0);
  }
 
  if (env.print_uid)
- printf("%-6d", event->uid);
+ printf("%-6d", event.uid);
 
  char type = '-';
- switch (event->type) {
+ switch (event.type) {
  case TCP_EVENT_TYPE_CONNECT:
  type = 'C';
  break;
@@ -210,11 +217,11 @@ static void handle_event(void *ctx, int cpu, void *data, __u32 data_sz)
  }
 
  printf("%c %-6d %-12.12s %-2d %-16s %-16s %-4d %-4d\n",
- type, event->pid, event->task,
- event->af == AF_INET ? 4 : 6,
- inet_ntop(event->af, &s, src, sizeof(src)),
- inet_ntop(event->af, &d, dst, sizeof(dst)),
- ntohs(event->sport), ntohs(event->dport));
+ type, event.pid, event.task,
+ event.af == AF_INET ? 4 : 6,
+ inet_ntop(event.af, &s, src, sizeof(src)),
+ inet_ntop(event.af, &d, dst, sizeof(dst)),
+ ntohs(event.sport), ntohs(event.dport));
 }
 
 static void handle_lost_events(void *ctx, int cpu, __u64 lost_cnt)