Re-visiting SKIP_TEST_BOGUS_ADDR in tests/ipc_msg.c

[Dylan Jhung]

On Sat, Sep 12, 2020 at 07:19:00PM +0800, Dmitry V. Levin wrote:
> On Fri, Sep 11, 2020 at 06:10:35PM +0800, Ruinland ChuanTzu Tsai wrote:
> > Hi all,
> > 
> > In glibc's 2.32 implementation, the syscall wrapper code now will ac-
> > cess the `buf` for transforming data types into kernel desired ones :
> > 
> > https://sourceware.org/git/?p=glibc.git;a=blob;f=sysdeps/unix/sysv/linux/msgctl.c;h=0776472d5e01dea3d4a90e5f025f5074e10d0250;hb=HEAD
> > 
> > which is introduced in the commit 3283f711 :
> > https://sourceware.org/git/?p=glibc.git;a=commit;f=sysdeps/unix/sysv/linux/msgctl.c;h=3283f711132eaadc4f04bd8c1d84c910c29ba066
> > 
> > This will definitely triggers the segmentation fault in user space
> > first instead of triggering EFAULT inside Linux kernel on _every_
> > platform.
> 
> Apparently, the conversion happens only on those architectures where
> glibc supports 32-bit time_t, that is, where __TIMESIZE == 32.
> 
> On these architectures disabling of TEST_MSGCTL_BOGUS_ADDR cures the
> segfault, but sadly it isn't enough to fix the test because glibc
> performs the time_t conversion and passes a structure at a different
> address in memory to the system call.
> 
> 
> -- 
> ldv

Hi ldv,

In my opinion, I think that we should remove the "TEST_MSGCTL_BOGUS_ADDR" test case in ipc_msg.c.
And just like you said in the paragraph above, 
this test case fails because that glibc will access the parameter and make some conversion of that parameter.

Accessing the parameter is totally a valid thing that glibc can do.
So, if we want to test the kernel behavior, we should use syscall(), instead.
https://man7.org/linux/man-pages/man2/syscall.2.html

This issue had already been pointed out when this test case was created.
We could find the ref below:
https://lists.strace.io/pipermail/strace-devel/2016-September/005612.html

If you are agree with that, I can come up with a patch to fix this issue.

Best,
Dylan Jhong