Return EISDIR when trying to create a path ending in / with open

[hoodmane]

If we open a path that in a / and we're about to create a file, instead return EISDIR.

[sbc100]

lgtm % comments

[dschuff]

It looks like this test is failing with ASan:
https://logs.chromium.org/logs/emscripten-releases/buildbucket/cr-buildbucket/8728149317242328273/+/u/Emscripten_testsuite__ASan_/stdout
(and SAFE_HEAP, I imagine it's the same issue: https://logs.chromium.org/logs/emscripten-releases/buildbucket/cr-buildbucket/8728149317242328273/+/u/Emscripten_testsuite__SAFE_HEAP_/stdout)

It looks like there's a null deref in open(). It may very well be pre-existing, but just exposed by this test.

[hoodmane]

I'll look into it (unless someone else fixes it first).

[hoodmane]

This is enough to reproduce the asan failure:

#include <fcntl.h>

int main() {
  open("./does-not-exist/", O_CREAT);
}

[sbc100]

This is enough to reproduce the asan failure:

#include <fcntl.h>

int main() {
  open("./does-not-exist/", O_CREAT);
}

Can you share the command line flags needed?

[sbc100]

Oh thats because if you specify O_CREAT you also need to specify that mode argument. If you don't the open syscall will read the mode from uninitialized memory.

open is actually variadic. So specifying O_CREAT with a mode is like using print without enough argments.

[sbc100]

From https://man7.org/linux/man-pages/man2/open.2.html:

The mode argument must be supplied if O_CREAT or O_TMPFILE is
specified in flags; if it is not supplied, some arbitrary
bytes from the stack will be applied as the file mode.