Re: faccessat and AT_SYM_NOFOLLOW

[u-wsnj@aetey.se]

On Thu, Sep 25, 2014 at 12:01:10PM -0400, Rich Felker wrote:
>    to get the file ownership and mode and performs its own access
>    permissions check in userspace. This is imprecise and does not
>    respect ACLs or any other advanced permission models provided by

Of course, that's plainly wrong.

> So my conclusion? There are some moderate-level documentation errors.
> glibc implements the flag, but not correctly. The changes I would
> recommend to the documentation:
> 
> 1. Document that AT_SYM_NOFOLLOW is not standard for this function,
>    and is a glibc extension. (uclibc is just a copy of glibc code)
> 
> 2. Document that AT_SYM_NOFOLLOW and AT_EACCESS are emulated and
>    unreliable on glibc.
> 
> 3. Document that the man page is covering the POSIX/glibc function
>    details, and the kernel syscall does not support flags at all.
>    (This might aid in getting the kernel folks to add a new faccessat4
>    syscall that would do flags at the kernel level.)
> 
> Do these sound reasonable?

Yes (but I would look for a stronger wording than "unreliable" :)

> Issue 2: Should musl support or ignore the AT_SYM_NOFOLLOW with
> faccessat?

[your analysis looks for my eyes correct]

I would not bother implementing something which does not make sense
(worse, would mislead the programmers, iow inflicting damage instead
of doing any good).

Regards,
Rune