selftests/bpf: Prevent infinite loop in veristat when base file is too short

The following example forces veristat to loop indefinitely:

$ cat two-ok
file_name,prog_name,verdict,total_states
file-a,a,success,12
file-b,b,success,67

$ cat add-failure
file_name,prog_name,verdict,total_states
file-a,a,success,12
file-b,b,success,67
file-b,c,failure,32

$ veristat -C two-ok add-failure
  <does not return>

The loop is caused by handle_comparison_mode() not checking if `base`
variable points to `fallback_stats` prior advancing joined results
using `base`.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20230407154125.896927-1-eddyz87@gmail.com

diff --git a/tools/testing/selftests/bpf/veristat.c b/tools/testing/selftests/bpf/veristat.c
index 53d7ec16826845e39e77882fecd5c571bc1c71dd..e05954e20bbabd65be8a3d1cf443f9307890b4e4 100644 (file)
--- a/tools/testing/selftests/bpf/veristat.c
+++ b/tools/testing/selftests/bpf/veristat.c
@@ -1824,18 +1824,22 @@ static int handle_comparison_mode(void)
                        join->stats_b = comp;
                        i++;
                        j++;
-               } else if (comp == &fallback_stats || r < 0) {
+               } else if (base != &fallback_stats && (comp == &fallback_stats || r < 0)) {
                        join->file_name = base->file_name;
                        join->prog_name = base->prog_name;
                        join->stats_a = base;
                        join->stats_b = NULL;
                        i++;
-               } else {
+               } else if (comp != &fallback_stats && (base == &fallback_stats || r > 0)) {
                        join->file_name = comp->file_name;
                        join->prog_name = comp->prog_name;
                        join->stats_a = NULL;
                        join->stats_b = comp;
                        j++;
+               } else {
+                       fprintf(stderr, "%s:%d: should never reach here i=%i, j=%i",
+                               __FILE__, __LINE__, i, j);
+                       return -EINVAL;
                }
                env.join_stat_cnt += 1;
        }