From: Florian Weimer <fweimer@redhat.com>
To: Rich Felker <dalias@libc.org>
Cc: 39236@debbugs.gnu.org, musl@lists.openwall.com
Subject: Re: [musl] coreutils cp mishandles error return from lchmod
Date: Wed, 22 Jan 2020 16:08:26 +0100 [thread overview]
Message-ID: <87a76fjzpx.fsf@oldenburg2.str.redhat.com> (raw)
In-Reply-To: <20200122144243.GZ30412@brightrain.aerifal.cx> (Rich Felker's message of "Wed, 22 Jan 2020 09:42:43 -0500")
* Rich Felker:
> On Wed, Jan 22, 2020 at 03:34:18PM +0100, Florian Weimer wrote:
>> * Rich Felker:
>>
>> > coreutils should be opting to use the system-provided lchmod, which is
>> > safe, and correctly handling error returns (silently treating
>> > EOPNOTSUPP as success) rather than as hard errors.
>>
>> glibc's lchmod always returns ENOSYS (except on Hurd). I don't know how
>> lchmod is used in coreutils, but I suspect it is not particularly
>> useful.
>
> When preserving permissions (cp -p, archive extraction, etc.), you
> want lchmod to work correctly just for the purpose of *not* following
> the link and thereby unwantedly changing the permissions of the link
> target. But, fchmodat with AT_SYMLINK_NOFOLLOW works just as well and
> is standard, and that's really what coreutils should be using.
I think you misread what I wrote: lchmod *always* returns ENOSYS. Even
if the file is not a symbolic link. Likewise, fchmodat with
AT_SYMLINK_NOFOLLOW *always* returns ENOTSUP.
The reason for this is that the kernel does not provide a suitable
system call to implement this, even though some file systems allow a
mode change for symbolic links. I think we can do better, although I
should note that each time we implement such emulation in userspace, it
comes back to bite us eventually.
Thanks,
Florian
next prev parent reply other threads:[~2020-01-22 15:08 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-22 14:15 Rich Felker
2020-01-22 14:34 ` Florian Weimer
2020-01-22 14:42 ` Rich Felker
2020-01-22 15:08 ` Florian Weimer [this message]
2020-01-22 15:15 ` Rich Felker
2020-01-22 15:32 ` Florian Weimer
2020-01-22 16:07 ` Rich Felker
2020-01-22 16:19 ` Florian Weimer
2020-01-22 17:15 ` Rich Felker
2020-01-22 20:48 ` Florian Weimer
2020-01-22 20:56 ` Rich Felker
2020-01-22 21:05 ` Florian Weimer
2020-01-22 21:55 ` bug#39236: " Paul Eggert
2020-01-22 22:05 ` Rich Felker
2020-02-08 0:37 ` Paul Eggert
2020-02-12 11:50 ` Florian Weimer
2020-02-12 13:05 ` Rich Felker
2020-02-12 19:07 ` Rich Felker
2020-02-12 19:13 ` Florian Weimer
2020-02-12 19:59 ` A. Wilcox
2020-02-12 20:56 ` Rich Felker
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