Messages in this thread | | | Subject | 2.4.18-14smp sys_call_table not found by the LKM loader | Date | Mon, 21 Oct 2002 23:23:16 -0400 (EDT) | From | Haizhi Xu <> |
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Hi, Friends: I use linux kernel 2.4.18-14smp. I am trying a kernel module with a reference to sys_call_table as: extern void *sys_call_table[]; However, when loading the module into the kernel, the loader reports: unresolved symbol sys_call_table I read the following and related messages. My question is: Is it true that I can NOT reference sys_call_table[] from a kernel loadable module in 2.4.18-14smp or higher version kernels? Then if I need to intercept system calls, how should I do it? Thanks a lot for answers. Hai
Re: Two fixes for 2.4.19-pre5-ac3 Erik Tews (erik.tews@gmx.net) Mon, 8 Apr 2002 01:31:22 +0200
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On Sun, Apr 07, 2002 at 06:42:05PM +0100, Alan Cox wrote: > > And, unless this is reversed the OpenAFS kernel module won't load (it > > needs sys_call_table.): > > Correct. There was agreement a very long time ago that code should not patch > the syscall table (for one its not safe). AFS probably needs fixing so the > AFS syscall hook is exported portably and nicely in the syscall code.
I am really not an expert on kernel-programming but I remember that there was a security-hole in the ptrace-code with which one a local user could gain root access. And there was a little kernel-modul with a wrapper-function for the ptrace-syscall that made traces only possible if the user who was calling this syscall was root. So if I understand right if we don't export the syscall-table it is impossible to write such syscall-wrapper-functions and it requires to recompile the kernel and reboot the machiene to fix such an security-hole.
So wouldn't it be better to export the syscall-table and just write into the documentation that it is not a good idea to manipulate syscalls or write a compiler-makro that gives out a warning when such a module is beeing compiled.
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