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Jakub Sitnicki 2576f87066 bpf, netns: Fix use-after-free in pernet pre_exit callback
Iterating over BPF links attached to network namespace in pre_exit hook is
not safe, even if there is just one. Once link gets auto-detached, that is
its back-pointer to net object is set to NULL, the link can be released and
freed without waiting on netns_bpf_mutex, effectively causing the list
element we are operating on to be freed.

This leads to use-after-free when trying to access the next element on the
list, as reported by KASAN. Bug can be triggered by destroying a network
namespace, while also releasing a link attached to this network namespace.

| ==================================================================
| BUG: KASAN: use-after-free in netns_bpf_pernet_pre_exit+0xd9/0x130
| Read of size 8 at addr ffff888119e0d778 by task kworker/u8:2/177
|
| CPU: 3 PID: 177 Comm: kworker/u8:2 Not tainted 5.8.0-rc1-00197-ga0c04c9d1008-dirty #776
| Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS ?-20190727_073836-buildvm-ppc64le-16.ppc.fedoraproject.org-3.fc31 04/01/2014
| Workqueue: netns cleanup_net
| Call Trace:
|  dump_stack+0x9e/0xe0
|  print_address_description.constprop.0+0x3a/0x60
|  ? netns_bpf_pernet_pre_exit+0xd9/0x130
|  kasan_report.cold+0x1f/0x40
|  ? netns_bpf_pernet_pre_exit+0xd9/0x130
|  netns_bpf_pernet_pre_exit+0xd9/0x130
|  cleanup_net+0x30b/0x5b0
|  ? unregister_pernet_device+0x50/0x50
|  ? rcu_read_lock_bh_held+0xb0/0xb0
|  ? _raw_spin_unlock_irq+0x24/0x50
|  process_one_work+0x4d1/0xa10
|  ? lock_release+0x3e0/0x3e0
|  ? pwq_dec_nr_in_flight+0x110/0x110
|  ? rwlock_bug.part.0+0x60/0x60
|  worker_thread+0x7a/0x5c0
|  ? process_one_work+0xa10/0xa10
|  kthread+0x1e3/0x240
|  ? kthread_create_on_node+0xd0/0xd0
|  ret_from_fork+0x1f/0x30
|
| Allocated by task 280:
|  save_stack+0x1b/0x40
|  __kasan_kmalloc.constprop.0+0xc2/0xd0
|  netns_bpf_link_create+0xfe/0x650
|  __do_sys_bpf+0x153a/0x2a50
|  do_syscall_64+0x59/0x300
|  entry_SYSCALL_64_after_hwframe+0x44/0xa9
|
| Freed by task 198:
|  save_stack+0x1b/0x40
|  __kasan_slab_free+0x12f/0x180
|  kfree+0xed/0x350
|  process_one_work+0x4d1/0xa10
|  worker_thread+0x7a/0x5c0
|  kthread+0x1e3/0x240
|  ret_from_fork+0x1f/0x30
|
| The buggy address belongs to the object at ffff888119e0d700
|  which belongs to the cache kmalloc-192 of size 192
| The buggy address is located 120 bytes inside of
|  192-byte region [ffff888119e0d700, ffff888119e0d7c0)
| The buggy address belongs to the page:
| page:ffffea0004678340 refcount:1 mapcount:0 mapping:0000000000000000 index:0x0
| flags: 0x2fffe0000000200(slab)
| raw: 02fffe0000000200 ffffea00045ba8c0 0000000600000006 ffff88811a80ea80
| raw: 0000000000000000 0000000000100010 00000001ffffffff 0000000000000000
| page dumped because: kasan: bad access detected
|
| Memory state around the buggy address:
|  ffff888119e0d600: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
|  ffff888119e0d680: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
| >ffff888119e0d700: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
|                                                                 ^
|  ffff888119e0d780: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc
|  ffff888119e0d800: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
| ==================================================================

Remove the "fast-path" for releasing a link that got auto-detached by a
dying network namespace to fix it. This way as long as link is on the list
and netns_bpf mutex is held, we have a guarantee that link memory can be
accessed.

An alternative way to fix this issue would be to safely iterate over the
list of links and ensure there is no access to link object after detaching
it. But, at the moment, optimizing synchronization overhead on link release
without a workload in mind seems like an overkill.

Fixes: ab53cad90e ("bpf, netns: Keep a list of attached bpf_link's")
Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Yonghong Song <yhs@fb.com>
Link: https://lore.kernel.org/bpf/20200630164541.1329993-1-jakub@cloudflare.com
2020-06-30 10:53:42 -07:00
arch flexible-array member conversion patches for 5.8-rc2 2020-06-16 17:23:57 -07:00
block block: Replace zero-length array with flexible-array 2020-06-15 23:08:32 -05:00
certs .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
crypto Merge branch 'rwonce/rework' of git://git.kernel.org/pub/scm/linux/kernel/git/will/linux 2020-06-10 14:46:54 -07:00
Documentation dma-mapping: Add a new dma_need_sync API 2020-06-30 15:44:03 +02:00
drivers r8169: fix firmware not resetting tp->ocp_base 2020-06-20 17:31:26 -07:00
fs AFS fixes 2020-06-16 17:40:51 -07:00
include bpf: sockmap: Require attach_bpf_fd when detaching a program 2020-06-30 10:46:39 -07:00
init Kbuild updates for v5.8 (2nd) 2020-06-13 13:29:16 -07:00
ipc mmap locking API: use coccinelle to convert mmap_sem rwsem call sites 2020-06-09 09:39:14 -07:00
kernel bpf, netns: Fix use-after-free in pernet pre_exit callback 2020-06-30 10:53:42 -07:00
lib test_objagg: Fix potential memory leak in error handling 2020-06-15 13:32:11 -07:00
LICENSES LICENSES: Rename other to deprecated 2019-05-03 06:34:32 -06:00
mm Kbuild updates for v5.8 (2nd) 2020-06-13 13:29:16 -07:00
net bpf: sockmap: Require attach_bpf_fd when detaching a program 2020-06-30 10:46:39 -07:00
samples Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf 2020-06-17 13:26:55 -07:00
scripts scripts/decode_stacktrace: warn when modpath is needed but is unset 2020-06-15 15:37:24 -07:00
security ima: Replace zero-length array with flexible-array 2020-06-15 23:08:32 -05:00
sound ASoC: SOF: Replace zero-length array with flexible-array 2020-06-15 23:08:32 -05:00
tools selftests: bpf: Pass program to bpf_prog_detach in flow_dissector 2020-06-30 10:46:39 -07:00
usr bpfilter: match bit size of bpfilter_umh to that of the kernel 2020-05-17 18:52:01 +09:00
virt MIPS: 2020-06-12 11:05:52 -07:00
.clang-format block: add bio_for_each_bvec_all() 2020-05-25 11:25:24 +02:00
.cocciconfig
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore modpost: generate vmlinux.symvers and reuse it for the second modpost 2020-06-06 23:38:12 +09:00
.mailmap A fair amount of stuff this time around, dominated by yet another massive 2020-06-01 15:45:27 -07:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS mailmap: change email for Ricardo Ribalda 2020-05-25 18:59:59 -06:00
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: update email address for Felix Fietkau 2020-06-22 12:57:11 -07:00
Makefile Linux 5.8-rc1 2020-06-14 12:45:04 -07:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

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.