Subject: CVE-2021-47247: net/mlx5e: Fix use-after-free of encap entry in neigh update handler

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

net/mlx5e: Fix use-after-free of encap entry in neigh update handler

Function mlx5e_rep_neigh_update() wasn't updated to accommodate rtnl lock
removal from TC filter update path and properly handle concurrent encap
entry insertion/deletion which can lead to following use-after-free:

 [23827.464923] ==================================================================
 [23827.469446] BUG: KASAN: use-after-free in mlx5e_encap_take+0x72/0x140 [mlx5_core]
 [23827.470971] Read of size 4 at addr ffff8881d132228c by task kworker/u20:6/21635
 [23827.472251]
 [23827.472615] CPU: 9 PID: 21635 Comm: kworker/u20:6 Not tainted 5.13.0-rc3+ #5
 [23827.473788] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
 [23827.475639] Workqueue: mlx5e mlx5e_rep_neigh_update [mlx5_core]
 [23827.476731] Call Trace:
 [23827.477260]  dump_stack+0xbb/0x107
 [23827.477906]  print_address_description.constprop.0+0x18/0x140
 [23827.478896]  ? mlx5e_encap_take+0x72/0x140 [mlx5_core]
 [23827.479879]  ? mlx5e_encap_take+0x72/0x140 [mlx5_core]
 [23827.480905]  kasan_report.cold+0x7c/0xd8
 [23827.481701]  ? mlx5e_encap_take+0x72/0x140 [mlx5_core]
 [23827.482744]  kasan_check_range+0x145/0x1a0
 [23827.493112]  mlx5e_encap_take+0x72/0x140 [mlx5_core]
 [23827.494054]  ? mlx5e_tc_tun_encap_info_equal_generic+0x140/0x140 [mlx5_core]
 [23827.495296]  mlx5e_rep_neigh_update+0x41e/0x5e0 [mlx5_core]
 [23827.496338]  ? mlx5e_rep_neigh_entry_release+0xb80/0xb80 [mlx5_core]
 [23827.497486]  ? read_word_at_a_time+0xe/0x20
 [23827.498250]  ? strscpy+0xa0/0x2a0
 [23827.498889]  process_one_work+0x8ac/0x14e0
 [23827.499638]  ? lockdep_hardirqs_on_prepare+0x400/0x400
 [23827.500537]  ? pwq_dec_nr_in_flight+0x2c0/0x2c0
 [23827.501359]  ? rwlock_bug.part.0+0x90/0x90
 [23827.502116]  worker_thread+0x53b/0x1220
 [23827.502831]  ? process_one_work+0x14e0/0x14e0
 [23827.503627]  kthread+0x328/0x3f0
 [23827.504254]  ? _raw_spin_unlock_irq+0x24/0x40
 [23827.505065]  ? __kthread_bind_mask+0x90/0x90
 [23827.505912]  ret_from_fork+0x1f/0x30
 [23827.506621]
 [23827.506987] Allocated by task 28248:
 [23827.507694]  kasan_save_stack+0x1b/0x40
 [23827.508476]  __kasan_kmalloc+0x7c/0x90
 [23827.509197]  mlx5e_attach_encap+0xde1/0x1d40 [mlx5_core]
 [23827.510194]  mlx5e_tc_add_fdb_flow+0x397/0xc40 [mlx5_core]
 [23827.511218]  __mlx5e_add_fdb_flow+0x519/0xb30 [mlx5_core]
 [23827.512234]  mlx5e_configure_flower+0x191c/0x4870 [mlx5_core]
 [23827.513298]  tc_setup_cb_add+0x1d5/0x420
 [23827.514023]  fl_hw_replace_filter+0x382/0x6a0 [cls_flower]
 [23827.514975]  fl_change+0x2ceb/0x4a51 [cls_flower]
 [23827.515821]  tc_new_tfilter+0x89a/0x2070
 [23827.516548]  rtnetlink_rcv_msg+0x644/0x8c0
 [23827.517300]  netlink_rcv_skb+0x11d/0x340
 [23827.518021]  netlink_unicast+0x42b/0x700
 [23827.518742]  netlink_sendmsg+0x743/0xc20
 [23827.519467]  sock_sendmsg+0xb2/0xe0
 [23827.520131]  ____sys_sendmsg+0x590/0x770
 [23827.520851]  ___sys_sendmsg+0xd8/0x160
 [23827.521552]  __sys_sendmsg+0xb7/0x140
 [23827.522238]  do_syscall_64+0x3a/0x70
 [23827.522907]  entry_SYSCALL_64_after_hwframe+0x44/0xae
 [23827.523797]
 [23827.524163] Freed by task 25948:
 [23827.524780]  kasan_save_stack+0x1b/0x40
 [23827.525488]  kasan_set_track+0x1c/0x30
 [23827.526187]  kasan_set_free_info+0x20/0x30
 [23827.526968]  __kasan_slab_free+0xed/0x130
 [23827.527709]  slab_free_freelist_hook+0xcf/0x1d0
 [23827.528528]  kmem_cache_free_bulk+0x33a/0x6e0
 [23827.529317]  kfree_rcu_work+0x55f/0xb70
 [23827.530024]  process_one_work+0x8ac/0x14e0
 [23827.530770]  worker_thread+0x53b/0x1220
 [23827.531480]  kthread+0x328/0x3f0
 [23827.532114]  ret_from_fork+0x1f/0x30
 [23827.532785]
 [23827.533147] Last potentially related work creation:
 [23827.534007]  kasan_save_stack+0x1b/0x40
 [23827.534710]  kasan_record_aux_stack+0xab/0xc0
 [23827.535492]  kvfree_call_rcu+0x31/0x7b0
 [23827.536206]  mlx5e_tc_del_fdb_flow+0x577/0xef0 [mlx5_core]
 [23827.537305]  mlx5e_flow_put+0x49/0x80 [mlx5_core]
 [23827.538290]  mlx5e_delete_flower+0x6d1/0xe60 [mlx5_core]
 [23827.539300]  tc_setup_cb_destroy+0x18e/0x2f0
 [23827.540144]  fl_hw_destroy_filter+0x1d2/0x310 [cls_flower]
 [23827.541148]  __fl_delete+0x4dc/0x660 [cls_flower]
 [23827.541985]  fl_delete+0x97/0x160 [cls_flower]
 [23827.542782]  tc_del_tfilter+0x7ab/0x13d0
 [23827.543503]  rtnetlink_rcv_msg+0x644/0x8c0
 [23827.544257]  netlink_rcv_skb+0x11d/0x340
 [23827.544981]  netlink_unicast+0x42b/0x700
 [23827.545700]  netlink_sendmsg+0x743/0xc20
 [23827.546424]  sock_sendmsg+0xb2/0xe0
 [23827.547084]  ____sys_sendmsg+0x590/0x770
 [23827.547850]  ___sys_sendmsg+0xd8/0x160
 [23827.548606]  __sys_sendmsg+0xb7/0x140
 [23827.549303]  do_syscall_64+0x3a/0x70
 [23827.549969]  entry_SYSCALL_64_after_hwframe+0x44/0xae
 [23827.550853]
 [23827.551217] The buggy address belongs to the object at ffff8881d1322200
 [23827.551217]  which belongs to the cache kmalloc-256 of size 256
 [23827.553341] The buggy address is located 140 bytes inside of
 [23827.553341]  256-byte region [ffff8881d1322200, ffff8881d1322300)
 [23827.555747] The buggy address belongs to the page:
 [23827.556847] page:00000000898762aa refcount:1 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x1d1320
 [23827.558651] head:00000000898762aa order:2 compound_mapcount:0 compound_pincount:0
 [23827.559961] flags: 0x2ffff800010200(slab|head|node=0|zone=2|lastcpupid=0x1ffff)
 [23827.561243] raw: 002ffff800010200 dead000000000100 dead000000000122 ffff888100042b40
 [23827.562653] raw: 0000000000000000 0000000000200020 00000001ffffffff 0000000000000000
 [23827.564112] page dumped because: kasan: bad access detected
 [23827.565439]
 [23827.565932] Memory state around the buggy address:
 [23827.566917]  ffff8881d1322180: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 [23827.568485]  ffff8881d1322200: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 [23827.569818] >ffff8881d1322280: fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb
 [23827.571143]                       ^
 [23827.571879]  ffff8881d1322300: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 [23827.573283]  ffff8881d1322380: fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc fc
 [23827.574654] ==================================================================

Most of the necessary logic is already correctly implemented by
mlx5e_get_next_valid_encap() helper that is used in neigh stats update
handler. Make the handler generic by renaming it to
mlx5e_get_next_matching_encap() and use callback to test whether flow is
matching instead of hardcoded check for 'valid' flag value. Implement
mlx5e_get_next_valid_encap() by calling mlx5e_get_next_matching_encap()
with callback that tests encap MLX5_ENCAP_ENTRY_VALID flag. Implement new
mlx5e_get_next_init_encap() helper by calling
mlx5e_get_next_matching_encap() with callback that tests encap completion
result to be non-error and use it in mlx5e_rep_neigh_update() to safely
iterate over nhe->encap_list.

Remove encap completion logic from mlx5e_rep_update_flows() since the encap
entries passed to this function are already guaranteed to be properly
initialized by similar code in mlx5e_get_next_init_encap().

The Linux kernel CVE team has assigned CVE-2021-47247 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 5.4 with commit 2a1f1768fa17 and fixed in 5.12.13 with commit b6447b72aca5
	Issue introduced in 5.4 with commit 2a1f1768fa17 and fixed in 5.13 with commit fb1a3132ee1a

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2021-47247
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	drivers/net/ethernet/mellanox/mlx5/core/en/rep/neigh.c
	drivers/net/ethernet/mellanox/mlx5/core/en/rep/tc.c
	drivers/net/ethernet/mellanox/mlx5/core/en/tc_tun_encap.c
	drivers/net/ethernet/mellanox/mlx5/core/en_tc.h

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/b6447b72aca571632e71bb73a797118d5ce46a93
	https://git.kernel.org/stable/c/fb1a3132ee1ac968316e45d21a48703a6db0b6c3