Re: [PATCH] NFSv4: Don't perform cached access checks before we've OPENed the file

[Al Viro <viro@ZenIV.linux.org.uk>]

On Sun, Dec 27, 2015 at 11:23:55AM -0500, Trond Myklebust wrote:
> > PS:
> >
> > I don't yet understand the point of execute_ok. It doesn't even consider the
> > uid.
> 
> ...or the group ownership or anything other than whether or not at
> least one execute bit is set. That's a convention that was set in the
> VFS a long time ago,

... by yourself, if you recall the patch that moved that check from
open_exec() to permission(), to get consistency between access() and
execve().

> and that Miklos' patches later pushed down into
> the filesystems.
> I'm OK with removing it, if someone can explain to me what it was
> intended to enforce in the first place, so that we can have a
> discussion about why it may be obsolete.

"Not even root gets to execute a binary that doesn't have a single exec bit
on it" goes _way_ back.  And not just in terms of Linux -
v5 /usr/sys/ken/fio.c:access() has
        if(u.u_uid == 0) {
                if(m == IEXEC && (ip->i_mode & 
                        (IEXEC | (IEXEC>>3) | (IEXEC>>6))) == 0)
                                return(1);
                return(0);
        }
so this had been introduced somewhere between v3 and v5 (AFAIK, v4 source
is gone and I hadn't crawled through the v4 manpages to see if that has
got a mention).  At the very least it's been there since Nov 26 1974...