[PATCH AUTOSEL 6.17-6.16] selftests/bpf: Fix incorrect array size calculation

[Sasha Levin <sashal@kernel.org>]

From: Jiayuan Chen <jiayuan.chen@linux.dev>

[ Upstream commit f85981327a90c51e76f60e073cb6648b2f167226 ]

The loop in bench_sockmap_prog_destroy() has two issues:

1. Using 'sizeof(ctx.fds)' as the loop bound results in the number of
   bytes, not the number of file descriptors, causing the loop to iterate
   far more times than intended.

2. The condition 'ctx.fds[0] > 0' incorrectly checks only the first fd for
   all iterations, potentially leaving file descriptors unclosed. Change
   it to 'ctx.fds[i] > 0' to check each fd properly.

These fixes ensure correct cleanup of all file descriptors when the
benchmark exits.

Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Jiayuan Chen <jiayuan.chen@linux.dev>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20250909124721.191555-1-jiayuan.chen@linux.dev

Closes: https://lore.kernel.org/bpf/aLqfWuRR9R_KTe5e@stanley.mountain/
Signed-off-by: Sasha Levin <sashal@kernel.org>
---

LLM Generated explanations, may be completely bogus:

YES
- `tools/testing/selftests/bpf/benchs/bench_sockmap.c:13` now pulls in
  `bpf_util.h`, matching the pattern already used by other BPF bench
  tests so the new `ARRAY_SIZE()` usage compiles on every branch that
  carries this benchmark (introduced in `7b2fa44de5e71`, tagged around
  v6.16-rc1).
- `tools/testing/selftests/bpf/benchs/bench_sockmap.c:129` replaces the
  byte-counted `sizeof(ctx.fds)` loop bound with `ARRAY_SIZE(ctx.fds)`,
  stopping the loop after the five real descriptors instead of wandering
  into the struct’s counters and repeatedly closing fd 0 or large
  garbage values. That out-of-bounds iteration currently kills the
  test’s own stdin and can hand later socket allocations fd 0, so the
  cleanup path leaks every other socket.
- `tools/testing/selftests/bpf/benchs/bench_sockmap.c:130` now checks
  `ctx.fds[i] > 0` per element instead of reusing `ctx.fds[0]`, which
  fixes real leak scenarios when the first slot is zero (either after
  the stray `close(0)` above or when `create_pair()` fails before
  assigning `c1` but other sockets were opened).
- Fix stays confined to the selftest helper and mirrors existing bench
  code practices, so regression risk is negligible while restoring
  reliable cleanup for the new sockmap benchmark—exactly the sort of
  correctness fix stable trees keep so their shipped selftests actually
  work.

Natural next step: queue this for the stable branches that already
picked up `bench_sockmap.c` (v6.16+).

 tools/testing/selftests/bpf/benchs/bench_sockmap.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/bpf/benchs/bench_sockmap.c b/tools/testing/selftests/bpf/benchs/bench_sockmap.c
index 8ebf563a67a2b..cfc072aa7fff7 100644
--- a/tools/testing/selftests/bpf/benchs/bench_sockmap.c
+++ b/tools/testing/selftests/bpf/benchs/bench_sockmap.c
@@ -10,6 +10,7 @@
 #include <argp.h>
 #include "bench.h"
 #include "bench_sockmap_prog.skel.h"
+#include "bpf_util.h"
 
 #define FILE_SIZE (128 * 1024)
 #define DATA_REPEAT_SIZE 10
@@ -124,8 +125,8 @@ static void bench_sockmap_prog_destroy(void)
 {
 	int i;
 
-	for (i = 0; i < sizeof(ctx.fds); i++) {
-		if (ctx.fds[0] > 0)
+	for (i = 0; i < ARRAY_SIZE(ctx.fds); i++) {
+		if (ctx.fds[i] > 0)
 			close(ctx.fds[i]);
 	}
 
-- 
2.51.0