Loader path security #1012
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Loader path security #1012
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The M1 loader now passes the program executable name directly as x2, which is the third argument to `cosmo()`. From there it is assigned to `__myname`. `GetProgramExecutableName` now always returns `__myname`, and it is `InitProgramExecutableName`’s job to set that variable if it is not already assigned. `InitProgramExecutableName` now dies if `issetugid()` and `__myname` is null, pending a rework of the path-finding logic.
It prints its own name to stderr, not stdout. It also prints `GetProgramExecutableName()` for further debugging convenience.
mrdomino
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- Tries `KERN_PROC_PATHNAME` first on NetBSD/FreeBSD. - Tries procfs first, but now only on Linux. (You can have /proc on FreeBSD, but then again, /proc could be anything on non-Linux. An option here is to put non-Linux /proc after the issetugid check.) - If `issetugid()` and none of the secure methods have worked, sets the empty string and returns.
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Using `COSMOPOLITAN_PROGRAM_EXECUTABLE` without a `sys_faccessat` was rightly causing test failures. Now that it is no longer used by the loader, there seems little value in prioritizing it over argv[0], so just lump it in with "_".
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The ape loader now passes the program executable name directly as a register.
x2is used on aarch64,%rdxon x86_64. This is passed as the third argument tocosmo()(M1) orLaunch(non-M1) and is assigned to the global__program_executable_name.GetProgramExecutableNamenow returns this global's value, setting it if it is initially null.InitProgramExecutableNamefirst tries exotic, secure methods:KERN_PROC_PATHNAMEon FreeBSD/NetBSD, and/procon Linux. If those produce a reasonable response (i.e., not"/usr/bin/ape", which happens with the loader before this change), that is used. Otherwise, ifissetugid(), the empty string is used. Otherwise, the old argv/envp parsing code is run.The value returned from the loader is always the full absolute path of the binary to be executed, having passed through
realpath. For the non-M1 loader, this necessitated writingRealPath, which usesreadlinkatof"/proc/self/fd/[progfd]"on Linux,F_GETPATHon Xnu, and the__realpathsyscall on OpenBSD. On FreeBSD/NetBSD, it punts toGetProgramExecutableName, which is secure on those OSes.With the loader, all platforms now have a secure program executable name. With no loader or an old loader, everything still works as it did, but setuid/setgid is not supported if the insecure pathfinding code would have been needed.
Fixes #991.