linux-kernel - Re: [fs/exec] 80bd5afdd8: xfstests.generic.633.fail

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Date:   Mon, 31 Jan 2022 16:37:07 +0100
From:   Christian Brauner <brauner@...nel.org>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     kernel test robot <oliver.sang@...el.com>,
        Kees Cook <keescook@...omium.org>,
        Ariadne Conill <ariadne@...eferenced.org>,
        0day robot <lkp@...el.com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Rich Felker <dalias@...c.org>,
        Eric Biederman <ebiederm@...ssion.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        LKML <linux-kernel@...r.kernel.org>, lkp@...ts.01.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        stable@...r.kernel.org
Subject: Re: [fs/exec]  80bd5afdd8: xfstests.generic.633.fail

On Mon, Jan 31, 2022 at 03:19:22PM +0000, Matthew Wilcox wrote:
> On Mon, Jan 31, 2022 at 04:08:19PM +0100, Christian Brauner wrote:
> > On Mon, Jan 31, 2022 at 10:43:52PM +0800, kernel test robot wrote:
> > I can fix this rather simply in our upstream fstests with:
> > 
> > static char *argv[] = {
> > 	"",
> > };
> > 
> > I guess.
> > 
> > But doesn't
> > 
> > static char *argv[] = {
> > 	NULL,
> > };
> > 
> > seem something that should work especially with execveat()?
> 
> The problem is that the exec'ed program sees an argc of 0, which is the
> problem we're trying to work around in the kernel (instead of leaving
> it to ld.so to fix for suid programs).

Ok, just seems a bit more intuitive for path-based exec than for
fd-based execveat().

What's argv[0] supposed to contain in these cases?

1. execveat(fd, NULL, ..., AT_EMPTY_PATH)
2. execveat(fd, "my-file", ..., )

"" in both 1. and 2.?
"" in 1. and "my-file" in 2.?