GNU bug report logs - #72707
install: need_copy (for "-C") should use stat instead of lstat

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Frank Heckenbach <f.heckenbach <at> fh-soft.de>
To: bug-coreutils <at> gnu.org
Subject: install: need_copy (for "-C") should use stat instead of lstat
Date: Mon, 19 Aug 2024 04:44:52 +0200

install dereferences symlinks given as sources (and I think that's
good). The "-C" option, however, uses lstat rather than
stat in need_copy and returns true if !S_ISREG.

So the (dereferenced) file will always be copied despite "-C".

Even worse, since "-p" cannot be combined with "-C", the installed
file will always get a new timestamp which may trigger rebuilds
(e.g. if the file is a header) even if nothing was changed, e.g.:

% touch a
% ln -s a b
% install -C b c
% ls --time-style=+%T -l
total 0
-rw------- 1 frank frank 0 23:46:51 a
lrwxrwxrwx 1 frank frank 1 23:46:54 b -> a
-rwxr-xr-x 1 frank frank 0 23:46:58 c
% install -C b c
% ls --time-style=+%T -l
total 0
-rw------- 1 frank frank 0 23:46:51 a
lrwxrwxrwx 1 frank frank 1 23:46:54 b -> a
-rwxr-xr-x 1 frank frank 0 23:47:06 c
% install -C b c
% ls --time-style=+%T -l
total 0
-rw------- 1 frank frank 0 23:46:51 a
lrwxrwxrwx 1 frank frank 1 23:46:54 b -> a
-rwxr-xr-x 1 frank frank 0 23:47:08 c
%

I asked Kamil Dudka who implemented "-C" originally and he pointed
out that requiring both the files to be regular files was suggested
by Jim Meyering in the review:
https://lists.gnu.org/archive/html/bug-coreutils/2009-02/msg00106.html

However, I don't see a real reason there, only his question:
"Have you considered requiring that both files be `regular', too?"

I don't know if install didn't dereference symlinks back then, but
now that it does, it seems consistent to dereference them in the
check as well, i.e. use stat rather than lstat.

Message #10 received at 72707-done <at> debbugs.gnu.org (full text, mbox):

From: Pádraig Brady <P <at> draigBrady.com>
To: Frank Heckenbach <f.heckenbach <at> fh-soft.de>, 72707-done <at> debbugs.gnu.org
Subject: Re: bug#72707: install: need_copy (for "-C") should use stat instead
 of lstat
Date: Mon, 19 Aug 2024 12:48:37 +0100

[Message part 1 (text/plain, inline)]

On 19/08/2024 03:44, Frank Heckenbach wrote:
> install dereferences symlinks given as sources (and I think that's
> good). The "-C" option, however, uses lstat rather than
> stat in need_copy and returns true if !S_ISREG.
> 
> So the (dereferenced) file will always be copied despite "-C".
> 
> Even worse, since "-p" cannot be combined with "-C", the installed
> file will always get a new timestamp which may trigger rebuilds
> (e.g. if the file is a header) even if nothing was changed, e.g.:
> 
> % touch a
> % ln -s a b
> % install -C b c
> % ls --time-style=+%T -l
> total 0
> -rw------- 1 frank frank 0 23:46:51 a
> lrwxrwxrwx 1 frank frank 1 23:46:54 b -> a
> -rwxr-xr-x 1 frank frank 0 23:46:58 c
> % install -C b c
> % ls --time-style=+%T -l
> total 0
> -rw------- 1 frank frank 0 23:46:51 a
> lrwxrwxrwx 1 frank frank 1 23:46:54 b -> a
> -rwxr-xr-x 1 frank frank 0 23:47:06 c
> % install -C b c
> % ls --time-style=+%T -l
> total 0
> -rw------- 1 frank frank 0 23:46:51 a
> lrwxrwxrwx 1 frank frank 1 23:46:54 b -> a
> -rwxr-xr-x 1 frank frank 0 23:47:08 c
> %
> 
> I asked Kamil Dudka who implemented "-C" originally and he pointed
> out that requiring both the files to be regular files was suggested
> by Jim Meyering in the review:
> https://lists.gnu.org/archive/html/bug-coreutils/2009-02/msg00106.html
> 
> However, I don't see a real reason there, only his question:
> "Have you considered requiring that both files be `regular', too?"
> 
> I don't know if install didn't dereference symlinks back then, but
> now that it does, it seems consistent to dereference them in the
> check as well, i.e. use stat rather than lstat.

I agree with your arguments to change this.

I'm not sure if the suggestion above about regular files,
was meant to preclude symlinks.

Marking this as done,
and I'll apply the attached later.

thanks,
Pádraig

[install-C-deref.patch (text/x-patch, attachment)]

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