From e32e6f02168f2ad7991eb5d160d312d2001520c8 Mon Sep 17 00:00:00 2001 From: Hongfu Li Date: Sat, 9 May 2026 16:03:28 +0800 Subject: [PATCH] selftests/cgroup: Fix cg_read_strcmp() empty string comparison cg_read_strcmp() allocated a buffer sized to strlen(expected) + 1, then passed it to read_text() which calls read(fd, buf, size-1). When comparing against an empty string (""), strlen("") = 0 gives a 1-byte buffer, and read() is asked to read 0 bytes. The file content is never actually read, so strcmp("", buf) always returns 0 regardless of the real content. This caused cg_test_proc_killed() to always report the cgroup as empty immediately, making OOM tests pass without verifying that processes were killed. Signed-off-by: Hongfu Li Signed-off-by: Tejun Heo --- tools/testing/selftests/cgroup/lib/cgroup_util.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/tools/testing/selftests/cgroup/lib/cgroup_util.c b/tools/testing/selftests/cgroup/lib/cgroup_util.c index 6a7295347e90..42f54936f4bb 100644 --- a/tools/testing/selftests/cgroup/lib/cgroup_util.c +++ b/tools/testing/selftests/cgroup/lib/cgroup_util.c @@ -106,8 +106,9 @@ int cg_read_strcmp(const char *cgroup, const char *control, /* Handle the case of comparing against empty string */ if (!expected) return -1; - else - size = strlen(expected) + 1; + + /* needs size > 1, otherwise cg_read() reads 0 bytes */ + size = (expected[0] == '\0') ? 2 : strlen(expected) + 1; buf = malloc(size); if (!buf)