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51b82141ff
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Kumar Kartikeya Dwivedi 51b82141ff bpf: Fix UAF due to race between btf_try_get_module and load_module 
[ Upstream commit 18688de203 ]

While working on code to populate kfunc BTF ID sets for module BTF from
its initcall, I noticed that by the time the initcall is invoked, the
module BTF can already be seen by userspace (and the BPF verifier). The
existing btf_try_get_module calls try_module_get which only fails if
mod->state == MODULE_STATE_GOING, i.e. it can increment module reference
when module initcall is happening in parallel.

Currently, BTF parsing happens from MODULE_STATE_COMING notifier
callback. At this point, the module initcalls have not been invoked.
The notifier callback parses and prepares the module BTF, allocates an
ID, which publishes it to userspace, and then adds it to the btf_modules
list allowing the kernel to invoke btf_try_get_module for the BTF.

However, at this point, the module has not been fully initialized (i.e.
its initcalls have not finished). The code in module.c can still fail
and free the module, without caring for other users. However, nothing
stops btf_try_get_module from succeeding between the state transition
from MODULE_STATE_COMING to MODULE_STATE_LIVE.

This leads to a use-after-free issue when BPF program loads
successfully in the state transition, load_module's do_init_module call
fails and frees the module, and BPF program fd on close calls module_put
for the freed module. Future patch has test case to verify we don't
regress in this area in future.

There are multiple points after prepare_coming_module (in load_module)
where failure can occur and module loading can return error. We
illustrate and test for the race using the last point where it can
practically occur (in module __init function).

An illustration of the race:

CPU 0                           CPU 1
			  load_module
			    notifier_call(MODULE_STATE_COMING)
			      btf_parse_module
			      btf_alloc_id	// Published to userspace
			      list_add(&btf_mod->list, btf_modules)
			    mod->init(...)
...				^
bpf_check		        |
check_pseudo_btf_id             |
  btf_try_get_module            |
    returns true                |  ...
...                             |  module __init in progress
return prog_fd                  |  ...
...                             V
			    if (ret < 0)
			      free_module(mod)
			    ...
close(prog_fd)
 ...
 bpf_prog_free_deferred
  module_put(used_btf.mod) // use-after-free

We fix this issue by setting a flag BTF_MODULE_F_LIVE, from the notifier
callback when MODULE_STATE_LIVE state is reached for the module, so that
we return NULL from btf_try_get_module for modules that are not fully
formed. Since try_module_get already checks that module is not in
MODULE_STATE_GOING state, and that is the only transition a live module
can make before being removed from btf_modules list, this is enough to
close the race and prevent the bug.

A later selftest patch crafts the race condition artifically to verify
that it has been fixed, and that verifier fails to load program (with
ENXIO).

Lastly, a couple of comments:

 1. Even if this race didn't exist, it seems more appropriate to only
    access resources (ksyms and kfuncs) of a fully formed module which
    has been initialized completely.

 2. This patch was born out of need for synchronization against module
    initcall for the next patch, so it is needed for correctness even
    without the aforementioned race condition. The BTF resources
    initialized by module initcall are set up once and then only looked
    up, so just waiting until the initcall has finished ensures correct
    behavior.

Fixes: 541c3bad8d ("bpf: Support BPF ksym variables in kernel modules")
Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20220114163953.1455836-2-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
2022-04-08 14:23:24 +02:00
arch ARM: configs: multi_v5_defconfig: re-enable DRM_PANEL and FB_xxx 2022-04-08 14:23:23 +02:00
block block: don't delete queue kobject before its children 2022-04-08 14:23:07 +02:00
certs certs: Add support for using elliptic curve keys for signing modules 2021-08-23 19:55:42 +03:00
crypto crypto: authenc - Fix sleep in atomic context in decrypt_tail 2022-04-08 14:23:05 +02:00
Documentation vsprintf: Fix %pK with kptr_restrict == 0 2022-04-08 14:23:18 +02:00
drivers udmabuf: validate ubuf->pagecount 2022-04-08 14:23:24 +02:00
fs f2fs: fix compressed file start atomic write may cause data corruption 2022-04-08 14:23:11 +02:00
include firmware: ti_sci: Fix compilation failure when CONFIG_TI_SCI_PROTOCOL is not defined 2022-04-08 14:23:16 +02:00
init init: make unknown command line param message clearer 2021-11-18 19:17:11 +01:00
ipc ipc/sem: do not sleep with a spin lock held 2022-02-08 18:34:03 +01:00
kernel bpf: Fix UAF due to race between btf_try_get_module and load_module 2022-04-08 14:23:24 +02:00
lib vsprintf: Fix %pK with kptr_restrict == 0 2022-04-08 14:23:18 +02:00
LICENSES LICENSES/dual/CC-BY-4.0: Git rid of "smart quotes" 2021-07-15 06:31:24 -06:00
mm mm/kmemleak: reset tag when compare object pointer 2022-04-08 14:22:56 +02:00
net rfkill: make new event layout opt-in 2022-04-08 14:23:00 +02:00
samples samples/landlock: Fix path_list memory leak 2022-04-08 14:22:59 +02:00
scripts kconfig: fix failing to generate auto.conf 2022-02-23 12:03:20 +01:00
security KEYS: trusted: Avoid calling null function trusted_key_exit 2022-04-08 14:23:09 +02:00
sound ASoC: amd: Fix reference to PCM buffer address 2022-04-08 14:23:22 +02:00
tools bpftool: Only set obj->skeleton on complete success 2022-04-08 14:23:24 +02:00
usr usr/include/Makefile: add linux/nfc.h to the compile-test coverage 2022-02-01 17:27:15 +01:00
virt KVM: Fix lockdep false negative during host resume 2022-03-16 14:23:40 +01:00
.clang-format clang-format: Update with the latest for_each macro list 2021-05-12 23:32:39 +02:00
.cocciconfig
.get_maintainer.ignore
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: ignore only top-level modules.builtin 2021-05-02 00:43:35 +09:00
.mailmap mailmap: add Andrej Shadura 2021-10-18 20:22:03 -10:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Daniel Drake to credits 2021-09-21 08:34:58 +03:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS MAINTAINERS: adjust file entry for of_net.c after movement 2022-03-08 19:12:53 +01:00
Makefile Linux 5.15.32 2022-03-28 09:58:46 +02:00
README

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.