This change modifies the fish safety check surrounding execve / spawn so
it can run shell scripts having concatenated binary content. We're using
the same safety check as FreeBSD /bin/sh [1] and the Z-shell [5]. POSIX
was recently revised to require this behavior:
"The input file may be of any type, but the initial portion of the
file intended to be parsed according to the shell grammar (XREF to
XSH 2.10.2 Shell Grammar Rules) shall consist of characters and
shall not contain the NUL character. The shell shall not enforce
any line length limits."
"Earlier versions of this standard required that input files to the
shell be text files except that line lengths were unlimited.
However, that was overly restrictive in relation to the fact that
shells can parse a script without a trailing newline, and in
relation to a common practice of concatenating a shell script
ending with an 'exit' or 'exec $command' with a binary data payload
to form a single-file self-extracting archive." [2] [3]
One example use case of such scripts, is the Cosmopolitan C Library [4]
which configuse the GNU Linker to output a polyglot shell+binary format
that runs on Linux / Mac / Windows / FreeBSD / OpenBSD / NetBSD / BIOS.
Fixes jart/cosmopolitan#88
[1] freebsd/freebsd-src@ 9a1cd36
[2] http://austingroupbugs.net/view.php?id=1250
[3] http://austingroupbugs.net/view.php?id=1226#c4394
[4] https://justine.lol/cosmopolitan/index.html
[5] zsh-users/zsh@ 326d9c2
Allow more scripts without #!
Allow scripts without #!
ridiculousfish added a commit that referenced this pull request
Mar 27, 2021
This adds a test for shebangless support from #7802, cleans up some of its tricks, and includes it in the changelog.
ridiculousfish added a commit that referenced this pull request
Mar 28, 2021
This expands the heuristic introduced in #7802 to prevent implicitly passing files ending in .fish to /bin/sh.
ridiculousfish added a commit to ridiculousfish/fish-shell that referenced this pull request
May 31, 2021
This concerns the behavior of posix_spawn for shebangless scripts. At some point, glibc started executing them using `sh`, which is desirable for fish's shebangless support (see fish-shell#7802). On glibcs without that behavior the shebangless test fails. So this change disables posix_spawn on older glibcs. It's not easy to figure out when that happened but it definitely happens in glibc 2.28, and does not happen in glibc 2.17. Presumably the new behavior is present in glibc 2.24 (see BZ#23264) so that's the cutoff: posix_spawn is no longer allowed on glibc < 2.24. This fixes the noshebang test failures on Ubuntu Xenial and Centos 7. See discussion at bottom of fish-shell#8021.
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