libbpf-tools: Fix misaligned pointer accesses in fsslower

The perf buffer in fsslower doesn't maintain 8 byte alignment for
delta_us, end_ns, offset and size 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/fsslower.c

@@ -328,31 +328,38 @@ static void print_headers()
 
 static void handle_event(void *ctx, int cpu, void *data, __u32 data_sz)
 {
- const struct event *e = data;
+ struct event e;
  struct tm *tm;
  char ts[32];
  time_t t;
 
+ if (data_sz < sizeof(e)) {
+ printf("Error: packet too small\n");
+ return;
+ }
+ /* Copy data as alignment in the perf buffer isn't guaranteed. */
+ memcpy(&e, data, sizeof(e));
+
  if (csv) {
- printf("%lld,%s,%d,%c,", e->end_ns, e->task, e->pid, file_op[e->op]);
- if (e->size == LLONG_MAX)
+ printf("%lld,%s,%d,%c,", e.end_ns, e.task, e.pid, file_op[e.op]);
+ if (e.size == LLONG_MAX)
  printf("LL_MAX,");
  else
- printf("%zd,", e->size);
- printf("%lld,%lld,%s\n", e->offset, e->delta_us, e->file);
+ printf("%zd,", e.size);
+ printf("%lld,%lld,%s\n", e.offset, e.delta_us, e.file);
  return;
  }
 
  time(&t);
  tm = localtime(&t);
  strftime(ts, sizeof(ts), "%H:%M:%S", tm);
 
- printf("%-8s %-16s %-7d %c ", ts, e->task, e->pid, file_op[e->op]);
- if (e->size == LLONG_MAX)
+ printf("%-8s %-16s %-7d %c ", ts, e.task, e.pid, file_op[e.op]);
+ if (e.size == LLONG_MAX)
  printf("%-7s ", "LL_MAX");
  else
- printf("%-7zd ", e->size);
- printf("%-8lld %7.2f %s\n", e->offset / 1024, (double)e->delta_us / 1000, e->file);
+ printf("%-7zd ", e.size);
+ printf("%-8lld %7.2f %s\n", e.offset / 1024, (double)e.delta_us / 1000, e.file);
 }
 
 static void handle_lost_events(void *ctx, int cpu, __u64 lost_cnt)