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

[Xi Ruoyao <xry111@xry111.site>]

On Tue, 2023-03-07 at 17:45 +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
> 
> Signed-off-by: abushwang <abushwangs@gmail.com>

Please use [PATCH v2] or v3, v4, ... into the title when you update the patch.

/* snip */

>  int
>  __shm_get_name (struct shmdir_name *result, const char *name, bool sem_prefix)
> @@ -54,9 +55,9 @@ __shm_get_name (struct shmdir_name *result, const char *name, bool sem_prefix)
>    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
> +  if (namelen == 0 || namelen > NAME_MAX || memchr (name, '/', namelen) != NULL

You can't just reject any namelen > NAMEMAX because a "may" clause in
the specification.  You may only do that if the allocation fails.

What you are doing is like: the specification of a capacitor says it may
(not "must" or "shall"!) blow up if the temperature is > 90C, then you
add a bomb into the capacitor which blows up when the temperature
reaches 90C.  It's definitely wrong. 

I was not telling you to make the code more compact.

-- 
Xi Ruoyao <xry111@xry111.site>
School of Aerospace Science and Technology, Xidian University