Paul W. Rankin <[email protected]> writes:
> On 2021-03-28 18:14, Omar Polo wrote: >> Paul W. Rankin <[email protected]> writes: >>> The cgit about-filter doesn't want an executable to do e.g. the >>> Markdown conversation, rather it wants a script that will return the >>> command to perform this, e.g.: >>> #!/bin/sh >>> case "$1" in >>> (*.md) exec /bin/lowdown ;; >>> (*) exit ;; >>> esac >>> This works, i.e. README.md files are converted to HTML, but this >>> requires copying the sh binary into /var/www/bin, which is the >>> troubling part. >>> Is this an acceptable thing to do, security-wise? >> I don't know almost anything about cgit, but if that's really the >> problem you could statically-link a program that does the above (just a >> call to execl("/bin/lowdown", NULL); may be enough) and use that. > > Thanks Omar, I like this approach! I'm pretty green to C so this is > what I have (which doesn't work): > > #include <unistd.h> > int main(void) { > execl("/bin/lowdown", NULL); > } > > There is no HTML render but at least no errors, but cgit expects the > resulting HTML printed to STDOUT, so I wonder whether this requires a > return? Assuming that the shell script you posted actually works yes, that snippet (with a small tweak[0]) should work. Make sure it's statically linked. For reference, here's how I would do it $ cat <<EOF > my-cgit-filter.c #include <unistd.h> int main(void) { execl("/bin/lowdown", "lowdown", NULL); return 1; } EOF $ cc my-cgit-filter.c -o my-cgit-filter.c -static $ # check that it's actually statically linked $ ldd my-cgit-filter my-cgit-filter: Start End Type Open Ref GrpRef Name 000005196d856000 000005196d87b000 dlib 1 0 0 /tmp/my-cgit-filter -- Cheers [0]: if you compile your snippet, clang should warning about a missing sentinel, something along the lines of > warning: not enough variable arguments in 'execl' declaration to fit a > sentinel [-Wsentinel] > execl("/bin/lowdown", NULL); which should suggest the use of > execl("/bin/lowdown", "lowdown", NULL);
