[ Upstream commit a4fa458950b40d3849946daa32466392811a3716 ]

Make sure 'pos' is initialized to zero before calling kernel_write().

Fixes: d2ba09c17a06 ("net: add skeleton of bpfilter kernel module")
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Daniel Borkmann says:

====================
pull-request: bpf 2020-07-31

The following pull-request contains BPF updates for your *net* tree.

We've added 5 non-merge commits during the last 21 day(s) which contain
a total of 5 files changed, 126 insertions(+), 18 deletions(-).

The main changes are:

1) Fix a map element leak in HASH_OF_MAPS map type, from Andrii Nakryiko.

2) Fix a NULL pointer dereference in __btf_resolve_helper_id() when no
   btf_vmlinux is available, from Peilin Ye.

3) Init pos variable in __bpfilter_process_sockopt(), from Christoph Hellwig.

4) Fix a cgroup sockopt verifier test by specifying expected attach type,
   from Jean-Philippe Brucker.

Note that when net gets merged into net-next later on, there is a small
merge conflict in kernel/bpf/btf.c between commit 5b801dfb7feb ("bpf: Fix
NULL pointer dereference in __btf_resolve_helper_id()") from the bpf tree
and commit 138b9a0511c7 ("bpf: Remove btf_id helpers resolving") from the
net-next tree.

Resolve as follows: remove the old hunk with the __btf_resolve_helper_id()
function. Change the btf_resolve_helper_id() so it actually tests for a
NULL btf_vmlinux and bails out:

int btf_resolve_helper_id(struct bpf_verifier_log *log,
                          const struct bpf_func_proto *fn, int arg)
{
        int id;

        if (fn->arg_type[arg] != ARG_PTR_TO_BTF_ID || !btf_vmlinux)
                return -EINVAL;
        id = fn->btf_id[arg];
        if (!id || id > btf_vmlinux->nr_types)
                return -EINVAL;
        return id;
}

Let me know if you run into any others issues (CC'ing Jiri Olsa so he's in
the loop with regards to merge conflict resolution).
====================

Signed-off-by: David S. Miller <davem@davemloft.net>

__bpfilter_process_sockopt never initialized the pos variable passed
to the pipe write. This has been mostly harmless in the past as pipes
ignore the offset, but the switch to kernel_write now verified the
position, which can lead to a failure depending on the exact stack
initialization pattern. Initialize the variable to zero to make
rw_verify_area happy.

Fixes: 6955a76fbcd5 ("bpfilter: switch to kernel_write")
Reported-by: Christian Brauner <christian.brauner@ubuntu.com>
Reported-by: Rodrigo Madera <rodrigo.madera@gmail.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: Rodrigo Madera <rodrigo.madera@gmail.com>
Tested-by: Christian Brauner <christian.brauner@ubuntu.com>
Reviewed-by: Christian Brauner <christian.brauner@ubuntu.com>
Link: https://lore.kernel.org/bpf/20200730160900.187157-1-hch@lst.de

While pipes don't really need sb_writers projection, __kernel_write is an
interface better kept private, and the additional rw_verify_area does not
hurt here.

Signed-off-by: Christoph Hellwig <hch@lst.de>

It's not intuitively obvious that bpfilter_umh is a statically linked binary.
Mention the toolchain requirement in the Kconfig help, so people
have an easier time figuring out what's needed.

Signed-off-by: Valdis Kletnieks <valdis.kletnieks@vt.edu>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

The user mode helper should be compiled for the same architecture as
the kernel.

This Makefile reused the 'hostprogs' syntax by overriding HOSTCC with CC.
Use the new syntax 'userprogs' to fix the Makefile mess.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Acked-by: Sam Ravnborg <sam@ravnborg.org>

On Fedora, linking static glibc requires the glibc-static RPM package,
which is not part of the glibc-devel package.

CONFIG_CC_CAN_LINK does not check the capability of static linking,
so you can enable CONFIG_BPFILTER_UMH, then fail to build:

    HOSTLD  net/bpfilter/bpfilter_umh
  /usr/bin/ld: cannot find -lc
  collect2: error: ld returned 1 exit status

Add CONFIG_CC_CAN_LINK_STATIC, and make CONFIG_BPFILTER_UMH depend
on it.

Reported-by: Valdis Kletnieks <valdis.kletnieks@vt.edu>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Acked-by: Alexei Starovoitov <ast@kernel.org>

bpfilter_umh is built for the default machine bit of the compiler,
which may not match to the bit size of the kernel.

This happens in the scenario below:

You can use biarch GCC that defaults to 64-bit for building the 32-bit
kernel. In this case, Kbuild passes -m32 to teach the compiler to
produce 32-bit kernel space objects. However, it is missing when
building bpfilter_umh. It is built as a 64-bit ELF, and then embedded
into the 32-bit kernel.

The 32-bit kernel and 64-bit umh is a bad combination.

In theory, we can have 32-bit umh running on 64-bit kernel, but we do
not have a good reason to support such a usecase.

The best is to match the bit size between them.

Pass -m32 or -m64 to the umh build command if it is found in
$(KBUILD_CFLAGS). Evaluate CC_CAN_LINK against the kernel bit-size.

Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>

Pull SPDX updates from Greg KH:
 "Here are three SPDX patches for 5.7-rc1.

  One fixes up the SPDX tag for a single driver, while the other two go
  through the tree and add SPDX tags for all of the .gitignore files as
  needed.

  Nothing too complex, but you will get a merge conflict with your
  current tree, that should be trivial to handle (one file modified by
  two things, one file deleted.)

  All three of these have been in linux-next for a while, with no
  reported issues other than the merge conflict"

* tag 'spdx-5.7-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/spdx:
  ASoC: MT6660: make spdxcheck.py happy
  .gitignore: add SPDX License Identifier
  .gitignore: remove too obvious comments

A testing message was brought by 13d0f7b814d9 ("net/bpfilter: fix dprintf
usage for /dev/kmsg") but should've been deleted before patch submission.
Although it doesn't cause any harm to the code or functionality itself, it's
totally unpleasant to have it displayed on every loop iteration with no real
use case. Thus remove it unconditionally.

Fixes: 13d0f7b814d9 ("net/bpfilter: fix dprintf usage for /dev/kmsg")
Signed-off-by: Bruno Meneguele <bmeneg@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>