linux-kernel - Re: [PATCH 2/2] openat2: add OA2_INHERIT

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Message-ID: <7c620151-be12-4580-818e-86e8b7f46e09@yandex.ru>
Date: Thu, 25 Apr 2024 12:23:27 +0300
From: stsp <stsp2@...dex.ru>
To: Al Viro <viro@...iv.linux.org.uk>
Cc: linux-kernel@...r.kernel.org, Stefan Metzmacher <metze@...ba.org>,
 Eric Biederman <ebiederm@...ssion.com>, Andy Lutomirski <luto@...nel.org>,
 Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
 Jeff Layton <jlayton@...nel.org>, Chuck Lever <chuck.lever@...cle.com>,
 Alexander Aring <alex.aring@...il.com>,
 David Laight <David.Laight@...lab.com>, linux-fsdevel@...r.kernel.org,
 linux-api@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
 Christian Göttsche <cgzones@...glemail.com>
Subject: Re: [PATCH 2/2] openat2: add OA2_INHERIT_CRED flag

25.04.2024 05:31, Al Viro пишет:
> Incidentally, suppose you have the same process run with stdin opened
> (r/o) by root.  F_SETFD it to O_CLOEXEC, then use your open with
> dirfd being 0, pathname - "" and flags - O_RDWR.
I actually checked this with the test-case.
It seems to return ENOENT:


Breakpoint 1, openat2 (dirfd=0, pathname=0x7fffffffdbee "",
     how=0x7fffffffd5e0, size=24) at tst.c:13
13        return syscall(SYS_openat2, dirfd, pathname, how, size);
(gdb) fin
Run till exit from #0  openat2 (dirfd=0, pathname=0x7fffffffdbee "",
     how=0x7fffffffd5e0, size=24) at tst.c:13
0x000000000040167b in main (argc=3, argv=0x7fffffffd7b8) at tst.c:140
140        fd = openat2(0, efile, &how1, sizeof(how1));
Value returned is $1 = -1
(gdb) list
135        err = fcntl(0, F_SETFD, O_CLOEXEC);
136        if (err) {
137            perror("fcntl(F_SETFD)");
138            return EXIT_FAILURE;
139        }
140        fd = openat2(0, efile, &how1, sizeof(how1));
141        if (fd == -1) {
142            perror("openat2(1)");
143    //        return EXIT_FAILURE;
144        } else {
(gdb) p errno
$2 = 2


So it seems the creds can't be stolen
from a non-dir fd, but I wonder why
ENOENT is returned instead of ENOTDIR.
Such ENOENT is not dicumented in a
man page of openat2(), so I guess there
is some problem here even w/o my patch. :)