CVE-2021-47402

In the Linux kernel, the following vulnerability has been resolved: net:
sched: flower: protect fl_walk() with rcu Patch that refactored fl_walk()
to use idr_for_each_entry_continue_ul() also removed rcu protection of
individual filters which causes following use-after-free when filter is
deleted concurrently. Fix fl_walk() to obtain rcu read lock while iterating
and taking the filter reference and temporary release the lock while
calling arg->fn() callback that can sleep. KASAN trace: [ 352.773640]
================================================================== [
352.775041] BUG: KASAN: use-after-free in fl_walk+0x159/0x240 [cls_flower]
[ 352.776304] Read of size 4 at addr ffff8881c8251480 by task tc/2987 [
352.777862] CPU: 3 PID: 2987 Comm: tc Not tainted 5.15.0-rc2+ #2 [
352.778980] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS
rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014 [ 352.781022] Call
Trace: [ 352.781573] dump_stack_lvl+0x46/0x5a [ 352.782332]
print_address_description.constprop.0+0x1f/0x140 [ 352.783400] ?
fl_walk+0x159/0x240 [cls_flower] [ 352.784292] ? fl_walk+0x159/0x240
[cls_flower] [ 352.785138] kasan_report.cold+0x83/0xdf [ 352.785851] ?
fl_walk+0x159/0x240 [cls_flower] [ 352.786587]
kasan_check_range+0x145/0x1a0 [ 352.787337] fl_walk+0x159/0x240
[cls_flower] [ 352.788163] ? fl_put+0x10/0x10 [cls_flower] [ 352.789007] ?
__mutex_unlock_slowpath.constprop.0+0x220/0x220 [ 352.790102]
tcf_chain_dump+0x231/0x450 [ 352.790878] ?
tcf_chain_tp_delete_empty+0x170/0x170 [ 352.791833] ?
__might_sleep+0x2e/0xc0 [ 352.792594] ? tfilter_notify+0x170/0x170 [
352.793400] ? __mutex_unlock_slowpath.constprop.0+0x220/0x220 [ 352.794477]
tc_dump_tfilter+0x385/0x4b0 [ 352.795262] ? tc_new_tfilter+0x1180/0x1180 [
352.796103] ? __mod_node_page_state+0x1f/0xc0 [ 352.796974] ?
__build_skb_around+0x10e/0x130 [ 352.797826] netlink_dump+0x2c0/0x560 [
352.798563] ? netlink_getsockopt+0x430/0x430 [ 352.799433] ?
__mutex_unlock_slowpath.constprop.0+0x220/0x220 [ 352.800542]
__netlink_dump_start+0x356/0x440 [ 352.801397]
rtnetlink_rcv_msg+0x3ff/0x550 [ 352.802190] ? tc_new_tfilter+0x1180/0x1180
[ 352.802872] ? rtnl_calcit.isra.0+0x1f0/0x1f0 [ 352.803668] ?
tc_new_tfilter+0x1180/0x1180 [ 352.804344] ?
_copy_from_iter_nocache+0x800/0x800 [ 352.805202] ?
kasan_set_track+0x1c/0x30 [ 352.805900] netlink_rcv_skb+0xc6/0x1f0 [
352.806587] ? rht_deferred_worker+0x6b0/0x6b0 [ 352.807455] ?
rtnl_calcit.isra.0+0x1f0/0x1f0 [ 352.808324] ? netlink_ack+0x4d0/0x4d0 [
352.809086] ? netlink_deliver_tap+0x62/0x3d0 [ 352.809951]
netlink_unicast+0x353/0x480 [ 352.810744] ? netlink_attachskb+0x430/0x430 [
352.811586] ? __alloc_skb+0xd7/0x200 [ 352.812349]
netlink_sendmsg+0x396/0x680 [ 352.813132] ? netlink_unicast+0x480/0x480 [
352.813952] ? __import_iovec+0x192/0x210 [ 352.814759] ?
netlink_unicast+0x480/0x480 [ 352.815580] sock_sendmsg+0x6c/0x80 [
352.816299] ____sys_sendmsg+0x3a5/0x3c0 [ 352.817096] ?
kernel_sendmsg+0x30/0x30 [ 352.817873] ? __ia32_sys_recvmmsg+0x150/0x150 [
352.818753] ___sys_sendmsg+0xd8/0x140 [ 352.819518] ?
sendmsg_copy_msghdr+0x110/0x110 [ 352.820402] ? ___sys_recvmsg+0xf4/0x1a0 [
352.821110] ? __copy_msghdr_from_user+0x260/0x260 [ 352.821934] ?
_raw_spin_lock+0x81/0xd0 [ 352.822680] ? __handle_mm_fault+0xef3/0x1b20 [
352.823549] ? rb_insert_color+0x2a/0x270 [ 352.824373] ?
copy_page_range+0x16b0/0x16b0 [ 352.825209] ?
perf_event_update_userpage+0x2d0/0x2d0 [ 352.826190] ?
__fget_light+0xd9/0xf0 [ 352.826941] __sys_sendmsg+0xb3/0x130 [ 352.827613]
? __sys_sendmsg_sock+0x20/0x20 [ 352.828377] ?
do_user_addr_fault+0x2c5/0x8a0 [ 352.829184] ?
fpregs_assert_state_consistent+0x52/0x60 [ 352.830001] ?
exit_to_user_mode_prepare+0x32/0x160 [ 352.830845] do_syscall_64+0x35/0x80
[ 352.831445] entry_SYSCALL_64_after_hwframe+0x44/0xae [ 352.832331] RIP:
0033:0x7f7bee973c17 [ —truncated—