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To: Jason Wessel <jason.wessel@windriver.com>
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Subject: Re: [PATCH v2] pseudo: Upgrade to latest to fix openat() with a directory symlink [NAK]
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On Fri, 2 Aug 2019 11:27:45 -0500
Jason Wessel <jason.wessel@windriver.com> wrote:

> The sequence of openat() followed by an fstat() on the opened file
> handle, will erase the pseudo uid entry for the symlink, as shown by
> the following lstat() in test 5. The culprit appears to be the
> fstat(), but it could be something much more complex than that...
> The next step is to figure out why the recent change to openat() to
> address test case 1, caused this new problem.

I suspect I know that one, although I'm not sure I know the details.

Pseudo will destroy entries of incompatible directory-entry types; for
instance, if it has the same path listed as both a plain file and a
directory. But consider, from openat.c:

#ifdef PSEUDO_NO_REAL_AT_FUNCTIONS
                rc = real___xstat64(_STAT_VER, path, &buf);
#else           
                rc = real___fxstatat64(_STAT_VER, dirfd, path, &buf, 0);
#endif

Note that there's no lstat, and no AT_SYMLINK_NOFOLLOW. Which is to say,
these stats will be following the symlink even though O_NOFOLLOW was
set. I can probably patch this in a bit.

-s