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Subject[PATCH v3 net-next 0/2] bpfilter
Date
Hi All,

v2->v3:
- followed Luis's suggestion and significantly simplied first patch
with shmem_kernel_file_setup+kernel_write. Added kdoc for new helper
- fixed typos and race to access pipes with mutex
- tested with bpfilter being 'builtin'. CONFIG_BPFILTER_UMH=y|m both work.
Interesting to see a usermode executable being embedded inside vmlinux.
- it doesn't hurt to enable bpfilter in .config.
ip_setsockopt commands sent to usermode via pipes and -ENOPROTOOPT is
returned from userspace, so kernel falls back to original iptables code

v1->v2:
this patch set is almost a full rewrite of the earlier umh modules approach
The v1 of patches and follow up discussion was covered by LWN:
https://lwn.net/Articles/749108/

I believe the v2 addresses all issues brought up by Andy and others.
Mainly there are zero changes to kernel/module.c
Instead of teaching module loading logic to recognize special
umh module, let normal kernel modules execute part of its own
.init.rodata as a new user space process (Andy's idea)
Patch 1 introduces this new helper:
int fork_usermode_blob(void *data, size_t len, struct umh_info *info);
Input:
data + len == executable file
Output:
struct umh_info {
struct file *pipe_to_umh;
struct file *pipe_from_umh;
pid_t pid;
};

Advantages vs v1:
- the embedded user mode executable is stored as .init.rodata inside
normal kernel module. These pages are freed when .ko finishes loading
- the elf file is copied into tmpfs file. The user mode process is swappable.
- the communication between user mode process and 'parent' kernel module
is done via two unix pipes, hence protocol is not exposed to
user space
- impossible to launch umh on its own (that was the main issue of v1)
and impossible to be man-in-the-middle due to pipes
- bpfilter.ko consists of tiny kernel part that passes the data
between kernel and umh via pipes and much bigger umh part that
doing all the work
- 'lsmod' shows bpfilter.ko as usual.
'rmmod bpfilter' removes kernel module and kills corresponding umh
- signed bpfilter.ko covers the whole image including umh code

Few issues:
- the user can still attach to the process and debug it with
'gdb /proc/pid/exe pid', but 'gdb -p pid' doesn't work.
(a bit worse comparing to v1)
- tinyconfig will notice a small increase in .text
+766 | TEXT | 7c8b94806bec umh: introduce fork_usermode_blob() helper

Alexei Starovoitov (2):
umh: introduce fork_usermode_blob() helper
net: add skeleton of bpfilter kernel module

fs/exec.c | 38 ++++++++++---
include/linux/binfmts.h | 1 +
include/linux/bpfilter.h | 15 +++++
include/linux/umh.h | 12 ++++
include/uapi/linux/bpfilter.h | 21 +++++++
kernel/umh.c | 125 +++++++++++++++++++++++++++++++++++++++++-
net/Kconfig | 2 +
net/Makefile | 1 +
net/bpfilter/Kconfig | 16 ++++++
net/bpfilter/Makefile | 30 ++++++++++
net/bpfilter/bpfilter_kern.c | 111 +++++++++++++++++++++++++++++++++++++
net/bpfilter/main.c | 63 +++++++++++++++++++++
net/bpfilter/msgfmt.h | 17 ++++++
net/ipv4/Makefile | 2 +
net/ipv4/bpfilter/Makefile | 2 +
net/ipv4/bpfilter/sockopt.c | 42 ++++++++++++++
net/ipv4/ip_sockglue.c | 17 ++++++
17 files changed, 503 insertions(+), 12 deletions(-)
create mode 100644 include/linux/bpfilter.h
create mode 100644 include/uapi/linux/bpfilter.h
create mode 100644 net/bpfilter/Kconfig
create mode 100644 net/bpfilter/Makefile
create mode 100644 net/bpfilter/bpfilter_kern.c
create mode 100644 net/bpfilter/main.c
create mode 100644 net/bpfilter/msgfmt.h
create mode 100644 net/ipv4/bpfilter/Makefile
create mode 100644 net/ipv4/bpfilter/sockopt.c

--
2.9.5

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