[musl] hasmntopt function returns non-NULL when it shouldn't

[Bruno Haible <bruno@clisp.org>]

Hi,

The hasmntopt() function is documented in
https://www.gnu.org/software/libc/manual/html_node/mtab.html
and
https://man7.org/linux/man-pages/man3/hasmntopt.3.html

The implementation of this function in musl libc 1.2.5 returns a non-NULL
value also for some options that do *not* occur in the mount options string.

How to reproduce:
=============================== has.c ===============================
#include <mntent.h>
#include <string.h>
#include <assert.h>

int
main ()
{
  char options[] = "rw,nosuid,nodev,noexec,noatime,size=5120k,inode64";
  struct mntent me;
  me.mnt_opts = options;

  assert (hasmntopt (&me, "ro") == NULL);
  assert (hasmntopt (&me, "rw") == options + 0);
  assert (hasmntopt (&me, "atime") == NULL);
  assert (hasmntopt (&me, "no") == NULL);
  assert (hasmntopt (&me, "noatime") == options + 23);
  assert (hasmntopt (&me, "size") == options + 31);
  assert (hasmntopt (&me, "size=512") == NULL);
  assert (hasmntopt (&me, "size=5120k") == options + 31);
  assert (hasmntopt (&me, "inode64") == options + 42);

  return 0;
}
=====================================================================
$ gcc -Wall has.c
$ ./a.out

Expected result: No assertion failure. Like on glibc.

Actual result:
Assertion failed: hasmntopt (&me, "atime") == NULL (has.c: main: 14)

The mount options "atime" and "noatime" are pretty much the opposite of
each other (see https://man7.org/linux/man-pages/man8/mount.8.html).
Therefore in a program that tests for the "atime" option, it is wrong
to return the equivalent of true when the options string contains "noatime",
not "atime".

Bruno