From: Arnd Bergmann <arnd@arndb.de>
To: linasvepstas@gmail.com
Cc: Chris Metcalf <cmetcalf@tilera.com>,
GLIBC Devel <libc-alpha@sourceware.org>,
linux-kernel@vger.kernel.org, libc-ports@sourceware.org,
linux-api@vger.kernel.org, Roland McGrath <roland@redhat.com>,
Mike Frysinger <vapier@gentoo.org>
Subject: Re: [BUG] Generic syscalls -- chmod vs. fchmodat
Date: Tue, 25 Jan 2011 15:29:24 +0100 [thread overview]
Message-ID: <201101251529.24779.arnd@arndb.de> (raw)
In-Reply-To: <AANLkTikhKHnR+7DskxYqWXduX4=tpfgsfL4sNYq+4QDq@mail.gmail.com>
On Monday 24 January 2011, Linas Vepstas wrote:
> Chris, Arnd, all,
[adding linux-api list]
> Found a bug/incompatibility in the generic syscalls chmod implementation;
> not sure if this is a kernel bug or a glibc bug, or how to correctly resolve it.
>
> The new "generic chmod" implementation for glibc sends chmod to the
> kernel call sys_fchmodat with AT_FDCWD, instead of using the older
> "deprecated" chmod syscall. These two behave slightly differently: with
> the new implementation, the file "" (i.e. string of length zero) gets
> interpreted
> as . and so the syscall succeeds, setting perms on . The old syscall would
> return an errno=2 No such file or directory for this filename.
>
> My gut instinct is that this is a kernel bug, but am not so sure; perhaps this
> is "working as designed". I thought of submitting a patch to fs/namei.c to
> fix this, but then got lost in the details: there didn't seem to be
> any particularly
> good place to add this check. Meanwhile, a glibc test case (posix/tst-chmod.c)
> is failing as a result.
>
> Should we put a check for this funky non-filename into the glibc
> generic code, or into sys_chmodat? Recommendations?
My feeling is that it should be in glibc: as Mike mentioned, we don't normally
change the behavior of existing system calls unless they are obviously
broken to start with. If we want to keep fchmodat getting the implicit
"." directory, and at the same time keep fchmod returning an error, the fchmod
wrapper around fchmodat is the only place that can enforce this.
Arnd
WARNING: multiple messages have this Message-ID (diff)
From: Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org>
To: linasvepstas-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
Cc: Chris Metcalf <cmetcalf-kv+TWInifGbQT0dZR+AlfA@public.gmane.org>,
GLIBC Devel <libc-alpha-9JcytcrH/bA+uJoB2kUjGw@public.gmane.org>,
linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
libc-ports-9JcytcrH/bA+uJoB2kUjGw@public.gmane.org,
linux-api-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
Roland McGrath <roland-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
Mike Frysinger <vapier-aBrp7R+bbdUdnm+yROfE0A@public.gmane.org>
Subject: Re: [BUG] Generic syscalls -- chmod vs. fchmodat
Date: Tue, 25 Jan 2011 15:29:24 +0100 [thread overview]
Message-ID: <201101251529.24779.arnd@arndb.de> (raw)
In-Reply-To: <AANLkTikhKHnR+7DskxYqWXduX4=tpfgsfL4sNYq+4QDq-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
On Monday 24 January 2011, Linas Vepstas wrote:
> Chris, Arnd, all,
[adding linux-api list]
> Found a bug/incompatibility in the generic syscalls chmod implementation;
> not sure if this is a kernel bug or a glibc bug, or how to correctly resolve it.
>
> The new "generic chmod" implementation for glibc sends chmod to the
> kernel call sys_fchmodat with AT_FDCWD, instead of using the older
> "deprecated" chmod syscall. These two behave slightly differently: with
> the new implementation, the file "" (i.e. string of length zero) gets
> interpreted
> as . and so the syscall succeeds, setting perms on . The old syscall would
> return an errno=2 No such file or directory for this filename.
>
> My gut instinct is that this is a kernel bug, but am not so sure; perhaps this
> is "working as designed". I thought of submitting a patch to fs/namei.c to
> fix this, but then got lost in the details: there didn't seem to be
> any particularly
> good place to add this check. Meanwhile, a glibc test case (posix/tst-chmod.c)
> is failing as a result.
>
> Should we put a check for this funky non-filename into the glibc
> generic code, or into sys_chmodat? Recommendations?
My feeling is that it should be in glibc: as Mike mentioned, we don't normally
change the behavior of existing system calls unless they are obviously
broken to start with. If we want to keep fchmodat getting the implicit
"." directory, and at the same time keep fchmod returning an error, the fchmod
wrapper around fchmodat is the only place that can enforce this.
Arnd
next prev parent reply other threads:[~2011-01-25 14:30 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-01-24 19:57 [BUG] Generic syscalls -- chmod vs. fchmodat Linas Vepstas
2011-01-24 21:05 ` Roland McGrath
2011-01-24 21:32 ` Mike Frysinger
2011-01-25 14:29 ` Arnd Bergmann [this message]
2011-01-25 14:29 ` Arnd Bergmann
2011-01-25 17:45 ` Roland McGrath
2011-01-25 17:45 ` Roland McGrath
2011-01-25 18:21 ` Arnd Bergmann
2011-01-25 18:21 ` Arnd Bergmann
2011-01-25 18:34 ` Roland McGrath
2011-01-25 18:34 ` Roland McGrath
2011-01-25 20:04 ` Arnd Bergmann
2011-01-25 20:04 ` Arnd Bergmann
2011-01-25 18:52 ` Mike Frysinger
2011-01-25 18:52 ` Mike Frysinger
2011-01-25 19:56 ` Eric Blake
2011-01-25 19:56 ` Eric Blake
2011-01-25 20:31 ` Eric Blake
2011-01-25 20:31 ` Eric Blake
2011-01-25 21:32 ` Eric Blake
2011-01-25 21:32 ` Eric Blake
2011-01-25 22:10 ` Linas Vepstas
2011-02-10 18:12 ` Andries Brouwer
2011-02-10 18:17 ` Roland McGrath
2011-02-10 18:17 ` Roland McGrath
2011-02-11 9:11 ` Andreas Schwab
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