Meson: macOS: incorrect rpath handling for dependencies

[siriobalmelli]

rpath handling on macOS is incorrect in 2 ways:

• LC_RPATH pointing to the build dir is NOT stripped on ninja install
• LC_RPATH for dependencies is OMITTED

The first problem is trivial, but conceivably a security concern if an attacker can manipulate the filesystem at runtime and put a compromised library in the "build rpath" not sripped.

The second problem is critical, but only shows up when dependencies are in non-standard paths (e.g.: Nix).

reproduce with intra-project dependency

A straightforward is the ncp utility of nonlibc:

~ $ git clone https://github.com/siriobalmelli/nonlibc.git
~ $ cd nonlibc
nonlibc $ git checkout tags/v0.1.9b
nonlibc $ nix-build

You will see it builds and tests successfully, including the test for ncp.
For context, ncp is declared in util/meson.build:

ncp = executable('ncp', 'ncp.c',
        include_directories : inc,
        link_with : nonlibc,
        install : true)

test('ncp test',
    find_program('test_ncp.py'),
    args : ncp.full_path())

However, trying to execute the result throws a linker error:

nonlibc$ result/bin/ncp
dyld: Library not loaded: @rpath/libnonlibc.dylib
  Referenced from: /Users/siriobalmelli/nonlibc/result/bin/ncp
  Reason: image not found

NOTE that result is actually a symlink to the Nix build:

nonlibc$ readlink result
/nix/store/p7mmc0i21967k7a2hmxdm67mx36766a2-nonlibc

However, the linking dependency IS correctly declared and exported to pkgconfig by meson:

nonlibc$ pkg-config --libs result/lib/pkgconfig/nonlibc.pc 
-L/nix/store/p7mmc0i21967k7a2hmxdm67mx36766a2-nonlibc/lib -lnonlibc

By looking at the "load commands" of ncp we see the problem (some output elided for clarity):

nonlibc$ otool -l result/bin/ncp | grep -E '\s+(name|path)'
         name @rpath/libnonlibc.dylib (offset 24)
         path /private/tmp/nix-build-nonlibc.drv-0/nonlibc/build/src (offset 12)

Here we see a (correct) @rpath name for nonlibc, but then we see:

• a path directive pointing to the build directory (should have been stripped)
• no path directive pointing to /nix/store/p7mmc0i21967k7a2hmxdm67mx36766a2-nonlibc/lib

hack for intra-project dependencies

The can be ~fixed~ hacked by:

1. forcing a linker argument when we declare the dependecy in meson:

# Force dependers to have an rpath entry pointing to where we KNOW we'll install.
# This fixes both Nix and non-nix projects (providing 'prefix' is set correctly),
#+  and does OPAQUELY (depender doesn't have to add an 'install_rpath' directive).
rpath = get_option('prefix') + '/' + get_option('libdir')
nonlibc_dep_shared = declare_dependency(link_with : nonlibc,
                    include_directories : inc,
                    dependencies : deps,
                    link_args : '-Wl,-rpath,' + rpath)

1. changing the ncp definition to use dependencies instead of link_with:

ncp = executable('ncp', 'ncp.c',
        include_directories : inc,
        dependencies: nonlibc_dep_shared,
        install : true)

Here is what the build looks like (some output elided for clarity):

~ $ git clone https://github.com/siriobalmelli/nonlibc.git
~ $ cd nonlibc
nonlibc $ nix-build
nonlibc $ result/bin/ncp 
Usage: result/bin/ncp [OPTION]... SOURCE_FILE DEST_FILE
  or:  result/bin/ncp [OPTION]... SOURCE_FILE... DEST_DIR/
nonlibc $ otool -l result/bin/ncp | grep -E '\s+(name|path)'
         name @rpath/libnonlibc.dylib (offset 24)
         path /nix/store/0xvwwzz02ngn63hiqv825fg0kyh5vldv-nonlibc/lib (offset 12)
         path /private/tmp/nix-build-nonlibc.drv-0/nonlibc/build/src (offset 12)

reproduce with inter-project (cannot fix as above)

The above would be all well and good, but when importing a dependency which is NOT a meson subproject, using pkgconfig, there is no straightforward way to force meson to generate an rpath.

An example is memorywell which depends on nonlibc:

~ $ git clone https://github.com/siriobalmelli/nonlibc.git
~ $ git clone --branch=sirio https://github.com/siriobalmelli/memorywell.git
~ $ cd memorywell
memorywell $ nix-build -I ~
dyld: Library not loaded: @rpath/libnonlibc.dylib
  Referenced from: /private/tmp/nix-build-memorywell.drv-0/memorywell/build/test/well_test_shared
  Reason: image not found

This is easier to see building step-by-step inside a nix-shell:

memorywell $ nix-shell -I ~ --pure
[nix-shell:~/memorywell]$ CC=clang meson --buildtype=release build-release-clang
The Meson build system
Version: 0.44.0
Source dir: /Users/siriobalmelli/memorywell
Build dir: /Users/siriobalmelli/memorywell/build-release-clang
Build type: native build
Project name: memorywell
Native C compiler: clang (clang 4.0.1)
Build machine cpu family: x86_64
Build machine cpu: x86_64
Found pkg-config: /nix/store/7p159gq5b79cxwjcpw1z3wjfcw0bjwdi-pkg-config-0.29.2/bin/pkg-config (0.29.2)
Native dependency nonlibc found: YES 0.1.9
Configuring well_config.h using configuration
Dependency threads found: YES
Build targets in project: 26
Found ninja-1.8.2 at /nix/store/yxpay4bx8b8fccgvk21fnn15kglkfllk-ninja-1.8.2/bin/ninja
[nix-shell:~/memorywell]$ cd build-release-clang/
[nix-shell:~/memorywell/build-release-clang]$ ninja 
[nix-shell:~/memorywell/build-release-clang]$ otool -l test/well_test_shared | grep -E '\s+(name|path)'
         name @rpath/libmemorywell.dylib (offset 24)
         name @rpath/libnonlibc.dylib (offset 24)
         path /Users/siriobalmelli/memorywell/build-release-clang/src (offset 12)
[nix-shell:~/memorywell/build-release-clang]$ pkg-config --libs nonlibc 
-L/nix/store/dbxywb352yx39j15hk7kmlsxqwc520nm-nonlibc/lib -lnonlibc

As you can see above:

• meson finds the nonlibc dependency using pkgconfig
• pkgconfig gives the right link path
• ... this path is absent from the well_test_shared executable

proposal

I propose that rpath logic for macOS be modified to:

1. At build-time: dereference all dependencies objects into a (unique) list of all LC_RPATH entries to add into the binary's "load commands" section:
2. for intra-project dependencies these point to the build dir
3. for pkgconfig (and any other) dependencies, these point to the system tree

4. don't take any paths for granted, even if /usr/lib etc - always insert an LC_RPATH entry

5. At install-time, rewrite all intra-project LC_RPATH entries to point to get_option('prefix') + '/' + get_option('libdir')

[jpakkane]

Regarding option 2, we should probably do the same thing that CMake does. AFAIK they clear the rpath entry and only write one in if it has been specified with their equivalent of install_rpath.

[nirbheek]

LC_RPATH pointing to the build dir is NOT stripped on ninja install

This is fixed with meson 0.46.1 and newer.

LC_RPATH for dependencies is OMITTED

This is still a problem, doubly so because you can't set DYLD_LIBRARY_PATH or DYLD_FALLBACK_LIBRARY_PATH in new shells on macOS, so build environments can't set it at all.

This means that the rpath entries are all wrong, and you can't run any executables:

$ gtester
dyld: Library not loaded: @rpath/libglib-2.0.0.dylib
  Referenced from: /Library/Frameworks/GStreamer.framework/Versions/1.0/bin/gtester
  Reason: image not found

On macOS, we need to always set the absolute rpath to all libraries that are used by a binary. This is what Autotools does, and also what XCode does. Without this, meson is basically useless on macOS.

[jpakkane]

But is it also what CMake does?

[nirbheek]

But is it also what CMake does?

Yes, and cmake also gives you overrides to not run install_name_tool to rewrite the @rpath even after install. Not sure yet if we need that.

[ePirat]

I think it is fine to have the @rpath in the install_name of the libraries for the uninstalled version in the meson folder, and the correct rpath values in the binaries. But when installing the install_name has to be adjusted and the rpaths in the binaries removed, no?

(Optionally users probably should have a way to set the rpath and install_name for the installed stuff, similar to what CMake allows to do)

[nirbheek]

I think it is fine to have the @rpath in the install_name of the libraries for the uninstalled version in the meson folder, and the correct rpath values in the binaries. But when installing the install_name has to be adjusted and the rpaths in the binaries removed, no?

Yes. Specifically, the builddir rpaths are removed (which we already do) and new ones are added based on the external and internal dependencies (which we do not do). I have a WIP patch for this.

(Optionally users probably should have a way to set the rpath and install_name for the installed stuff, similar to what CMake allows to do)

One step at a time, please. We keep getting stuck trying to 'fix everything on macOS' (the exact meaning of which everyone disagrees on) and getting nothing done.

[ePirat]

One step at a time, please.

Sure, just wanted to make sure to point it out.

BTW is the build folder created by meson relocatable? I guess not?

[nirbheek]

BTW is the build folder created by meson relocatable? I guess not?

It is not.