Re: [Buildroot] [PATCH 05/13] support/scripts: fix and restrict conditions to accept merged dirs

["Yann E. MORIN" <yann.morin.1998@free.fr>]

Arnout, All,

On 2025-05-17 12:13 +0200, Arnout Vandecappelle spake thusly:
> On 17/05/2025 09:59, Yann E. MORIN wrote:
> > On 2025-05-14 18:58 +0200, Yann E. MORIN spake thusly:
> > > Currently, we accept that the merged usr is bqckward, i.e. that the
> > > /usr/bin, /usr/sbin, and /usr/lib entries be symlinks to, resp., /bin,
> > > /sbin, and /lib. We also allow either entries to be symlinks to other
> > > parts of the root. Both are accepted despite the comment at the top of
> > > the script explaining what should be accepted.
> > > 
> > > However, a properly merged usr is the other way around: /bin, /sbin, and
> > > /lib are the symlinks to resp. /usr/bin, /usr/sbin, and /usr/lib, and
> > > the latters are actual directories.
> > [--SNIP--]
> > > @@ -32,12 +29,21 @@ test_merged() {
> > >   	local dir2="${3}"
> > >   	local inode1 inode2
> > > +	# OK if missing first entry and second entry is an actual directory
> > > +	test -e "${root}${dir1}" || { test -d "${root}${dir2}" && return; }
> > > +
> > >   	inode1="$(stat -c '%i' "${root}${dir1}/." 2>/dev/null)"
> > >   	inode2="$(stat -c '%i' "${root}${dir2}/." 2>/dev/null)"
> > > -	test -z "${inode1}" || \
> > > -		test "${inode1}" = "${inode2}" || \
> > > -			printf '%s\n' "${dir1}"
> > > +	# OK if first entry is a symlink, second entry is a directoy, and
> > > +	# both have the same inode (once dereferenced)
> > > +	test -L "${root}${dir1}" \
> > > +	&& test -d "${root}${dir2}" \
> > > +	&& test "${inode1}" = "${inode2}" \
> > > +	&& return
> > > +
> > > +	# Otherwise, this directory is not merged
> > > +	printf '%s\n' "${dir1}"
> > 
> > This new test is still quite complex, and is in fact still wrong in
> > weird cases. For example, with BASE a custom skeleton or rootfs overlay,
> > if BASE/sbin and BASE/usr/sbin ar absolute symlinks to /usr/sbin, the
> > test above will accept BASE as being properly merged, while it is in
> > fact broken.
> > 
> > I'm preparing a v2 which greatly simplifies the test, and makes it cover
> > more (all, hopefully) cases.
> 
>  I guess the test should simply be:
> 
> test -L "${root}${dir1}" \
> && test -d "${root}${dir2}" \
> && test "$(readlink "${root}${dir1}")" = "${dir2}" \

This test for the target of the symlink is wrong: if dir1 is bin, and
points to /usr/bin, then this is wrong: we really want relative
symlinks.

> && return
> 
>  (which is not actually simpler... except that you can remove all the stat stuff)

I'm going with an even simpler, more strict solution, that simply
implements word-for-word our requirements. Indeed, I just drop all the
stat stuff that could get things wrong.

Regards,
Yann E. MORIN.

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