lib/tst_cgroup: fix short reads of mems/cpus

tst_cgroup_cpuset_read_files() is wrongly using sizeof on pointer
type to figure out length of buffer. On some systems there's
more content in cgroup mems/cpus, which leads to partial read
and subsequent EINVAL on write.

Also the retval buffer should be zero terminated, since buffer
can be passed uninitialized, subsequently leading to writing garbage
to cgroup and again hitting EINVAL.

Before:
  tst_test.c:1250: TINFO: Timeout per run is 0h 05m 00s
  tst_device.c:423: TINFO: No device is mounted at cgroup2
  tst_device.c:423: TINFO: No device is mounted at /tmp/cgroup_cst
  tst_cgroup.c:100: TINFO: Cgroup(cpuset) v1 mount at /tmp/cgroup_cst success
  safe_macros.c:458: TBROK: tst_cgroup.c:449: write(6,0x7fffc0425410,18446744073709551615) failed: EINVAL (22)
  tst_cgroup.c:173: TWARN: umount /tmp/cgroup_cst: EBUSY (16)
  tst_cgroup.c:175: TWARN: rmdir /tmp/cgroup_cst: EBUSY (16)
  tst_cgroup.c:178: TINFO: Cgroup v1 unmount success

After:
  tst_test.c:1250: TINFO: Timeout per run is 0h 05m 00s
  tst_device.c:423: TINFO: No device is mounted at cgroup2
  tst_device.c:423: TINFO: No device is mounted at /tmp/cgroup_cst
  tst_cgroup.c:100: TINFO: Cgroup(cpuset) v1 mount at /tmp/cgroup_cst success
  cpuset01.c:83: TPASS: cpuset test pass
  tst_cgroup.c:178: TINFO: Cgroup v1 unmount success

Signed-off-by: Jan Stancek <[email protected]>
Reviewed-by: Li Wang <[email protected]>

Author: jstancek

include/tst_cgroup.h

@@ -39,7 +39,9 @@ int  tst_cgroup_mem_swapacct_enabled(const char *cgroup_dir);
 void tst_cgroup_mem_set_maxswap(const char *cgroup_dir, long memsz);
 
 /* Set of functions to read/write cpuset controller files content */
-void tst_cgroup_cpuset_read_files(const char *cgroup_dir, const char *filename, char *retbuf);
-void tst_cgroup_cpuset_write_files(const char *cgroup_dir, const char *filename, const char *buf);
+void tst_cgroup_cpuset_read_files(const char *cgroup_dir, const char *filename,
+	char *retbuf, size_t retbuf_sz);
+void tst_cgroup_cpuset_write_files(const char *cgroup_dir, const char *filename,
+	const char *buf);
 
 #endif /* TST_CGROUP_H */

lib/tst_cgroup.c

@@ -393,7 +393,8 @@ void tst_cgroup_mem_set_maxswap(const char *cgroup_dir, long memsz)
 		tst_cgroup_set_knob(cgroup_dir, "memory.swap.max", memsz);
 }
 
-void tst_cgroup_cpuset_read_files(const char *cgroup_dir, const char *filename, char *retbuf)
+void tst_cgroup_cpuset_read_files(const char *cgroup_dir, const char *filename,
+	char *retbuf, size_t retbuf_sz)
 {
 	int fd;
 	char *cgroup_new_dir;
@@ -417,7 +418,8 @@ void tst_cgroup_cpuset_read_files(const char *cgroup_dir, const char *filename,
 			tst_brk(TBROK | TERRNO, "open %s", knob_path);
 	}
 
-	if (read(fd, retbuf, sizeof(retbuf)) < 0)
+	memset(retbuf, 0, retbuf_sz);
+	if (read(fd, retbuf, retbuf_sz) < 0)
 		tst_brk(TBROK | TERRNO, "read %s", knob_path);
 
 	close(fd);

testcases/kernel/mem/cpuset/cpuset01.c

@@ -51,9 +51,9 @@ static void test_cpuset(void)
 	unsigned long nmask[MAXNODES / BITS_PER_LONG] = { 0 };
 	char mems[BUFSIZ], buf[BUFSIZ];
 
-	tst_cgroup_cpuset_read_files(PATH_TMP_CG_CST, "cpus", buf);
+	tst_cgroup_cpuset_read_files(PATH_TMP_CG_CST, "cpus", buf, BUFSIZ);
 	tst_cgroup_cpuset_write_files(PATH_TMP_CG_CST, "cpus", buf);
-	tst_cgroup_cpuset_read_files(PATH_TMP_CG_CST, "mems", mems);
+	tst_cgroup_cpuset_read_files(PATH_TMP_CG_CST, "mems", mems, BUFSIZ);
 	tst_cgroup_cpuset_write_files(PATH_TMP_CG_CST, "mems", mems);
 	tst_cgroup_move_current(PATH_TMP_CG_CST);