elf: expand $ORIGIN in RUNPATH/RPATH entries

[alebcay]

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Follow-up to #17136. It's possible for RPATH or RUNPATH to have entries that contain $ORIGIN, which expands to the directory where the ELF object is located.

We need to expand $ORIGIN and search for dependencies in paths containing $ORIGIN, too.

[MikeMcQuaid]

Looks good to me so far! Will request a few more reviews here.

[MikeMcQuaid]

Suggested change

	local_paths = (path.patchelf_patcher.runpath || path.patchelf_patcher.rpath)&.split(":")&.map do |rp|
	# Expand instances of $ORIGIN in the R(UN)PATH
	rp.gsub "$ORIGIN", path.parent
	local_paths = (path.patchelf_patcher.runpath || path.patchelf_patcher.rpath)&.split(":")&.map do |runpath|
	runpath.gsub "$ORIGIN", path.parent

[carlocab]

You could move this #gsub call into the local_paths&.each block below, I think.

Also: I'm not sure if we want #gsub, since $ORIGIN is only replaced by the dynamic linker if it is the prefix of the path, IIUC.

[ZhongRuoyu]

I'm not sure if we want #gsub, since $ORIGIN is only replaced by the dynamic linker if it is the prefix of the path, IIUC.

$ORIGIN gets substituted even if it's not the prefix; check this. Or TL;DR: a quick example:

linuxbrew@9c46a48f740f:~/.linuxbrew/opt/python/bin$ patchelf --print-rpath python3.12
/home/linuxbrew/.linuxbrew/Cellar/[email protected]/3.12.3/lib
linuxbrew@9c46a48f740f:~/.linuxbrew/opt/python/bin$ ldd python3.12
	linux-vdso.so.1 (0x00007fff28bb6000)
	libpython3.12.so.1.0 => /home/linuxbrew/.linuxbrew/Cellar/[email protected]/3.12.3/lib/libpython3.12.so.1.0 (0x00007b09b6838000)
	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007b09b660c000)
	libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007b09b6523000)
	/home/linuxbrew/.linuxbrew/lib/ld.so => /lib64/ld-linux-x86-64.so.2 (0x00007b09b6eb9000)
linuxbrew@9c46a48f740f:~/.linuxbrew/opt/python/bin$ patchelf --set-rpath '$ORIGIN/../lib' python3.12
linuxbrew@9c46a48f740f:~/.linuxbrew/opt/python/bin$ ldd python3.12
	linux-vdso.so.1 (0x00007ffcba9d2000)
	libpython3.12.so.1.0 => /home/linuxbrew/.linuxbrew/Cellar/[email protected]/3.12.3/bin/./../lib/libpython3.12.so.1.0 (0x0000701941109000)
	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x0000701940edd000)
	libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x0000701940df4000)
	/home/linuxbrew/.linuxbrew/lib/ld.so => /lib64/ld-linux-x86-64.so.2 (0x000070194178a000)
linuxbrew@9c46a48f740f:~/.linuxbrew/opt/python/bin$ patchelf --set-rpath '/usr/bin/../../$ORIGIN/../lib' python3.12
linuxbrew@9c46a48f740f:~/.linuxbrew/opt/python/bin$ ldd python3.12
	linux-vdso.so.1 (0x00007ffc6119c000)
	libpython3.12.so.1.0 => /usr/bin/../..//home/linuxbrew/.linuxbrew/Cellar/[email protected]/3.12.3/bin/./../lib/libpython3.12.so.1.0 (0x00007cd2a2506000)
	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x00007cd2a22da000)
	libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00007cd2a21f1000)
	/home/linuxbrew/.linuxbrew/lib/ld.so => /lib64/ld-linux-x86-64.so.2 (0x00007cd2a2b8a000)

Also, as can be seen in the path expansion logic, two more such tokens exist: $PLATFORM and $LIB. See https://www.akkadia.org/drepper/dsohowto.pdf, page 40, paragraph "$ORIGIN is not the only DST available...". Though, I think they are less commonly seen and can be followed up later.

[alebcay]

Moved the expansion into the local_paths&.each block that follows, and replaced #gsub with just #sub (and only matches $ORIGIN from beginning of string for each path in the list).

[alebcay]

Ah, oops. Will switch it back to a gsub for anywhere in the string (looks like multiple occurrences of $ORIGIN are also accepted - can't imagine in what scenario such a case would occur, but not really harder for us to handle).

linuxbrew@ac7f2339ac92:~/.linuxbrew/opt/python/bin$ patchelf --set-rpath '$ORIGIN/../../../../../../..$ORIGIN/../lib' python3.12
linuxbrew@ac7f2339ac92:~/.linuxbrew/opt/python/bin$ ldd python3.12
	libpython3.12.so.1.0 => /home/linuxbrew/.linuxbrew/Cellar/[email protected]/3.12.3/bin/./../../../../../../../home/linuxbrew/.linuxbrew/Cellar/[email protected]/3.12.3/bin/./../lib/libpython3.12.so.1.0 (0x0000004002849000)
	libc.so.6 => /lib/x86_64-linux-gnu/libc.so.6 (0x0000004002ec4000)
	libm.so.6 => /lib/x86_64-linux-gnu/libm.so.6 (0x00000040030ef000)
	/home/linuxbrew/.linuxbrew/lib/ld.so => /lib64/ld-linux-x86-64.so.2 (0x0000004000000000)
linuxbrew@ac7f2339ac92:~/.linuxbrew/opt/python/bin$ file /home/linuxbrew/.linuxbrew/Cellar/[email protected]/3.12.3/bin/./../../../../../../../home/linuxbrew/.linuxbrew/Cellar/[email protected]/3.12.3/bin/./../lib/libpython3.12.so.1.0
/home/linuxbrew/.linuxbrew/Cellar/[email protected]/3.12.3/bin/./../../../../../../../home/linuxbrew/.linuxbrew/Cellar/[email protected]/3.12.3/bin/./../lib/libpython3.12.so.1.0: ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, BuildID[sha1]=34400f728c92b58b1adf2df38f5c3693b3bdc38c, not stripped

[ZhongRuoyu]

Thanks!

[Bo98]

I think technically ${ORIGIN} can happen, and strings like $ORIGINa are not substituted (must not be followed by [A-Za-z0-9_], unless in curly quotes).

glibc algorithm is here: https://github.com/bminor/glibc/blob/41903cb6f460d62ba6dd2f4883116e2a624ee6f8/elf/dl-load.c#L182-L228

[alebcay]

Moved the logic out into a separate function (and module) to make testing it easier, especially with the corner cases that have been noted so far.

[ZhongRuoyu]

Nice work!