Re: [apparmor] [PATCH v2 08/92] fs: new helper: simple_rename_timestamp

Seth Arnold
2023-07-06T21:10:02Z

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On Wed, Jul 05, 2023 at 08:04:41PM -0400, Jeff Layton wrote:
>
> I don't believe it's an issue. I've seen nothing in the POSIX spec that
> mandates that timestamp updates to different inodes involved in an
> operation be set to the _same_ value. It just says they must be updated.
>
> It's also hard to believe that any software would depend on this either,
> given that it's very inconsistent across filesystems today. AFAICT, this
> was mostly done in the past just as a matter of convenience.

I've seen this assumption in several programs:

mutt buffy.c
https://sources.debian.org/src/mutt/2.2.9-1/buffy.c/?hl=625#L625

if (mailbox->newly_created &&
(sb->st_ctime != sb->st_mtime || sb->st_ctime != sb->st_atime))
mailbox->newly_created = 0;

neomutt mbox/mbox.c
https://sources.debian.org/src/neomutt/20220429+dfsg1-4.1/mbox/mbox.c/?hl=1820#L1820

if (m->newly_created && ((st.st_ctime != st.st_mtime) || (st.st_ctime != st.st_atime)))
m->newly_created = false;

screen logfile.c
https://sources.debian.org/src/screen/4.9.0-4/logfile.c/?hl=130#L130

if ((!s->st_dev && !s->st_ino) || /* stat failed, that's new! */
!s->st_nlink || /* red alert: file unlinked */
(s->st_size < o.st_size) || /* file truncated */
(s->st_mtime != o.st_mtime) || /* file modified */
((s->st_ctime != o.st_ctime) && /* file changed (moved) */
!(s->st_mtime == s->st_ctime && /* and it was not a change */
o.st_ctime < s->st_ctime))) /* due to delayed nfs write */
{

nemo libnemo-private/nemo-vfs-file.c
https://sources.debian.org/src/nemo/5.6.5-1/libnemo-private/nemo-vfs-file.c/?hl=344#L344

/* mtime is when the contents changed; ctime is when the
* contents or the permissions (inc. owner/group) changed.
* So we can only know when the permissions changed if mtime
* and ctime are different.
*/
if (file->details->mtime == file->details->ctime) {
return FALSE;
}

While looking for more examples, I found a perl test that seems to suggest
that at least Solaris, AFS, AmigaOS, DragonFly BSD do as you suggest:
https://sources.debian.org/src/perl/5.36.0-7/t/op/stat.t/?hl=158#L140

Thanks

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