[PATCH] rt: fix shm_open not set ENAMETOOLONG when name exceeds {_POSIX_PATH_MAX}

[abush wang]

I have re-send this patch according to your suggest.

Thinks
abushwang

Xi Ruoyao <xry111@xry111.site> 于2023年3月7日周二 16:54写道：

> On Tue, 2023-03-07 at 16:32 +0800, abushwang via Libc-alpha wrote:
> > according to man-pages-posix-2017, shm_open() function may fail if the
> length
> > of the name argument exceeds {_POSIX_PATH_MAX} and set ENAMETOOLONG
>
> It's "may" fail, not "shall" fail.  POSIX 2017 says "may" means:
>
> may
>
> Describes a feature or behavior that is optional for an implementation
> that conforms to POSIX.1-2017. An application should not rely on the
> existence of the feature or behavior. An application that relies on such
> a feature or behavior cannot be assured to be portable across conforming
> implementations.
>
> We should not break existing programs just for a "may" clause.
>
> /* snip */
>
> >  int
> >  __shm_get_name (struct shmdir_name *result, const char *name, bool
> > sem_prefix)
> > @@ -50,13 +51,15 @@ __shm_get_name (struct shmdir_name *result, const
> > char *name, bool sem_prefix)
> >    while (name[0] == '/')
> >      ++name;
> >    namelen = strlen (name);
> > +  if (namelen > NAME_MAX)
> > +    return ENAMETOOLONG;
> >
> >    if (sem_prefix)
> >      alloc_buffer_copy_bytes (&buffer, "sem.", strlen ("sem."));
> >    alloc_buffer_copy_bytes (&buffer, name, namelen + 1);
> >    if (namelen == 0 || memchr (name, '/', namelen) != NULL
> >        || alloc_buffer_has_failed (&buffer))
>
> If you really want ENAMETOOLONG I guess you can check if namelen >
> NAME_MAX here (as a very long namelen would have caused an allocation
> failure).
>
> By the way if namelen <= NAME_MAX but alloc_buffer_has_failed (due to a
> high memory usage) should we say ENOSPC instead of EINVAL?  POSIX 2017
> says:
>
> [ENOSPC]
> There is insufficient space for the creation of the new shared memory
> object.
>
> > -    return -1;
> > +    return EINVAL;
> >    return 0;
> >  }
>
> --
> Xi Ruoyao <xry111@xry111.site>
> School of Aerospace Science and Technology, Xidian University
>