[PATCH] selftests: timers: skip raw_skew when adjtimex fails

[Daniel Syauqi <syauqicode@gmail.com>]

raw_skew reads frequency and offset data from adjtimex() without checking
whether either query succeeded. If a sandbox blocks the syscall, the
test can use uninitialized data and wait two minutes before producing a
misleading result.

Skip on either failure and report the syscall error. Preserve errno
across the newline printed after the second query.

Fixes: 51f91cbdf545 ("selftests/timers: Add clock skew estimation test from timetest suite")
Assisted-by: LLM Codex
Signed-off-by: Daniel Syauqi <syauqicode@gmail.com>
---
Tool assistance: OpenAI Codex helped identify the unchecked adjtimex()
returns, draft the fix and changelog, and create failure-path tests.
Prompt summary: Investigate the unchecked adjtimex() calls in raw_skew
and prepare and test a narrow selftest fix. The affected content is
raw_skew.c error handling and this changelog.

Tests: Built raw_skew with make. Forced EPERM at each adjtimex() call
separately with LD_PRELOAD; both runs skipped with exit status 4. A
normal raw_skew run passed, and targeted timer selftests had no failures.
The full kernel test suite was not run.

 tools/testing/selftests/timers/raw_skew.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/tools/testing/selftests/timers/raw_skew.c b/tools/testing/selftests/timers/raw_skew.c
index 0c87a8fb0..2ad5e2e35 100644
--- a/tools/testing/selftests/timers/raw_skew.c
+++ b/tools/testing/selftests/timers/raw_skew.c
@@ -19,7 +19,9 @@
  *   GNU General Public License for more details.
  */
 
+#include <errno.h>
 #include <stdio.h>
+#include <string.h>
 #include <unistd.h>
 #include <stdlib.h>
 #include <sys/time.h>
@@ -101,7 +103,8 @@ int main(int argc, char **argv)
 	}
 
 	tx1.modes = 0;
-	adjtimex(&tx1);
+	if (adjtimex(&tx1) < 0)
+		ksft_exit_skip("adjtimex failed: %s\n", strerror(errno));
 	get_monotonic_and_raw(&mon, &raw);
 	start = mon;
 	delta1 = diff_timespec(mon, raw);
@@ -116,7 +119,12 @@ int main(int argc, char **argv)
 	get_monotonic_and_raw(&mon, &raw);
 	end = mon;
 	tx2.modes = 0;
-	adjtimex(&tx2);
+	if (adjtimex(&tx2) < 0) {
+		int saved_errno = errno;
+
+		printf("\n");
+		ksft_exit_skip("adjtimex failed: %s\n", strerror(saved_errno));
+	}
 	delta2 = diff_timespec(mon, raw);
 
 	interval = diff_timespec(start, end);

base-commit: 602042bf29f6efde39cfb5fdd9289bf4854bc0c5
-- 
2.47.3