Date: Mon, 18 Sep 2023 23:38:18 +0200 From: Yuri <yuri@aetern.org> To: freebsd-hackers@freebsd.org Subject: Re: Error while building a kernel module with mkdir(2) Message-ID: <36d29d5c-43cd-4e77-9406-e786d08a79e2@aetern.org> In-Reply-To: <trinity-2c27b4d2-a301-466b-941e-2577e4886a49-1695071577376@3c-app-mailcom-lxa16> References: <trinity-2c27b4d2-a301-466b-941e-2577e4886a49-1695071577376@3c-app-mailcom-lxa16>
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Rocky Hotas wrote: > Hello! > I hope this is the right ML to discuss about this issue. I am trying to > build the example kernel module presented in paragraph 2.1 of > > Designing BSD Rootkits: An Introduction to Kernel Hacking > by Joseph Kong > > However, I get this error: > > mkdir_hook.c:42:9: error: implicit declaration of function 'mkdir' is invalid in C99 [-Werror,-Wimplicit-function-declaration] > return(mkdir(td, syscall_args)); > ^ > mkdir_hook.c:57:45: error: use of undeclared identifier 'mkdir' > sysent[SYS_mkdir].sy_call = (sy_call_t *)mkdir; > > mkdir(2) requires `#include <sys/stat.h>' and I added it (while it was > not in the code from the book), but nothing changes. That include is for userland that needs mkdir(2). Your wrapper likely wants to override the in-kernel sys_mkdir() defined in <sys/sysproto.h>. > What's still wrong? > > After this text, I paste the code and the Makefile (written following > https://docs.freebsd.org/en/books/arch-handbook/driverbasics/). > > Bye! > > Rocky > > > > === code: mkdir_hook.c === > > #include <sys/types.h> > #include <sys/param.h> /* defines used in kernel.h */ > #include <sys/proc.h> > #include <sys/module.h> > #include <sys/sysent.h> > #include <sys/kernel.h> /* types used in module initialization */ > #include <sys/systm.h> /* uprintf */ > #include <sys/syscall.h> > #include <sys/sysproto.h> > #include <sys/stat.h> /* mkdir(2) */ > > > /* mkdir system call hook. */ > static int > mkdir_hook(struct thread *td, void *syscall_args) > { > struct mkdir_args /* { > char *path; > int mode; > } */ *uap; > > uap = (struct mkdir_args *)syscall_args; > char path[255]; > size_t done; > int error; > error = copyinstr(uap->path, path, 255, &done); > > if (error != 0) > return(error); > /* Print a debug message. */ > uprintf("The directory \"%s\" will be created with the following" > " permissions: %o\n", path, uap->mode); > > return(mkdir(td, syscall_args)); > } > > /* The function called at load/unload. */ > static int > load(struct module *module, int cmd, void *arg) > { > int error = 0; > switch (cmd) { > case MOD_LOAD: > /* Replace mkdir with mkdir_hook. */ > sysent[SYS_mkdir].sy_call = (sy_call_t *)mkdir_hook; > break; > case MOD_UNLOAD: > /* Change everything back to normal. */ > sysent[SYS_mkdir].sy_call = (sy_call_t *)mkdir; > break; > > default: > error = EOPNOTSUPP; > break; > } > > return(error); > } > > static moduledata_t > mkdir_hook_mod = { > "mkdir_hook", /* module name */ > load, /* event handler */ > NULL /* extra data */ > }; > > DECLARE_MODULE(mkdir_hook, mkdir_hook_mod, SI_SUB_DRIVERS, SI_ORDER_MIDDLE); > > > > === Makefile === > > KMOD=mkdir_hook > SRCS=mkdir_hook.c > .include <bsd.kmod.mk> >
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