Re: [RFC][PATCH] sysctl: Remove the sysctl system call

[Jann Horn]

+Kostya (code owner for LLVM sanitizer_common) as FYI

On Wed, Oct 2, 2019 at 12:54 AM Eric W. Biederman <ebiederm@xxxxxxxxxxxx> wrote:
> Kees Cook <keescook@xxxxxxxxxxxx> writes:
> > On Tue, Oct 01, 2019 at 01:36:32PM -0500, Eric W. Biederman wrote:
[...]
> > I think you can actually take this further and remove (or at least
> > empty) the uapi/linux/sysctl.h file too.
[...]
> I would make it a followup that removes uapi/linux/sysctl.h.  I don't
> see anything in it that isn't about the sysctl system call.  I will keep
> it a separate patch as I can imagine something silly that needs the
> header file to compile.  A separate patch would make a revert easier
> if we find something like that.

Unfortunately, I think that header (or at least parts of it) has to
stay around for now:

Looking through the search results for linux/sysctl.h (ignoring
glibc's sys/sysctl.h, which pulls in linux/sysctl.h, because almost
all of those hits are conditional includes for BSD systems) on
codesearch.debian.net, I noticed that e.g. the ASAN code that GCC and
LLVM use pulls in linux/sysctl.h and uses things from it:

https://github.com/llvm-mirror/compiler-rt/blob/124fd5d9aff57cf47bf077df81ad939b289acc6e/lib/sanitizer_common/sanitizer_platform_limits_posix.cpp#L1063

And indeed, after replacing /usr/include/linux/sysctl.h with an empty
file, a build of LLVM's runtime library component (compiler-rt) (git
HEAD version) falls over with error spew about __sysctl_args:

====================
$ cmake -G Ninja -DCMAKE_BUILD_TYPE=Release
-DLLVM_ENABLE_PROJECTS='clang;compiler-rt' -DCMAKE_C_COMPILER=clang-7
-DCMAKE_CXX_COMPILER=clang++-7 -DLLVM_TARGETS_TO_BUILD="X86"
-DLLVM_USE_LINKER=lld-7 -DBUILD_SHARED_LIBS=Off ../llvm
[...]
$ ninja -j64
FAILED: projects/compiler-rt/lib/sanitizer_common/CMakeFiles/RTSanitizerCommonNoTermination.i386.dir/sanitizer_platform_limits_posix.cpp.o
[...]
[...]/compiler-rt/lib/sanitizer_common/sanitizer_platform_limits_posix.cpp:1063:17:
error: use of undeclared identifier '__sysctl_args'
CHECK_TYPE_SIZE(__sysctl_args);
                ^
[...]/compiler-rt/lib/sanitizer_common/sanitizer_platform_limits_posix.cpp:1064:23:
error: use of undeclared identifier '__sysctl_args'
CHECK_SIZE_AND_OFFSET(__sysctl_args, name);
                      ^
[...]/compiler-rt/lib/sanitizer_common/sanitizer_platform_limits_posix.cpp:1064:1:
error: expected expression
CHECK_SIZE_AND_OFFSET(__sysctl_args, name);
^
[...]/compiler-rt/lib/sanitizer_common/sanitizer_platform_limits_posix.h:1438:34:
note: expanded from macro 'CHECK_SIZE_AND_OFFSET'
                 sizeof(((CLASS *)NULL)->MEMBER));                \
                                 ^
[...]/compiler-rt/lib/sanitizer_common/sanitizer_platform_limits_posix.cpp:1064:23:
error: unknown type name '__sysctl_args'
CHECK_SIZE_AND_OFFSET(__sysctl_args, name);
                      ^
====================