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

[Pádraig Brady]

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
Description: Text Data