[PATCH] exec: Check __FMODE_EXEC instead of in_execve for LSMs

[Jann Horn]

On Wed, Jan 24, 2024 at 8:22 PM Kees Cook <keescook at chromium.org> wrote:
> After commit 978ffcbf00d8 ("execve: open the executable file before
> doing anything else"), current->in_execve was no longer in sync with the
> open(). This broke AppArmor and TOMOYO which depend on this flag to
> distinguish "open" operations from being "exec" operations.
>
> Instead of moving around in_execve, switch to using __FMODE_EXEC, which
> is where the "is this an exec?" intent is stored. Note that TOMOYO still
> uses in_execve around cred handling.

I think this is wrong. When CONFIG_USELIB is enabled, the uselib()
syscall will open a file with __FMODE_EXEC but without going through
execve(). From what I can tell, there are no bprm hooks on this path.

I don't know if it _matters_ much, given that it'll only let you
read/execute stuff from files with valid ELF headers, but still.