[PATCH 5.16 102/227] ipv6: fix data-race in fib6_info_hw_flags_set / fib6_purge_rt

Greg Kroah-Hartman
2022-02-21T09:53:11Z

From: Eric Dumazet <edumazet@google.com>

commit d95d6320ba7a51d61c097ffc3bcafcf70283414e upstream.

Because fib6_info_hw_flags_set() is called without any synchronization,
all accesses to gi6->offload, fi->trap and fi->offload_failed
need some basic protection like READ_ONCE()/WRITE_ONCE().

BUG: KCSAN: data-race in fib6_info_hw_flags_set / fib6_purge_rt

read to 0xffff8881087d5886 of 1 bytes by task 13953 on cpu 0:
fib6_drop_pcpu_from net/ipv6/ip6_fib.c:1007 [inline]
fib6_purge_rt+0x4f/0x580 net/ipv6/ip6_fib.c:1033
fib6_del_route net/ipv6/ip6_fib.c:1983 [inline]
fib6_del+0x696/0x890 net/ipv6/ip6_fib.c:2028
__ip6_del_rt net/ipv6/route.c:3876 [inline]
ip6_del_rt+0x83/0x140 net/ipv6/route.c:3891
__ipv6_dev_ac_dec+0x2b5/0x370 net/ipv6/anycast.c:374
ipv6_dev_ac_dec net/ipv6/anycast.c:387 [inline]
__ipv6_sock_ac_close+0x141/0x200 net/ipv6/anycast.c:207
ipv6_sock_ac_close+0x79/0x90 net/ipv6/anycast.c:220
inet6_release+0x32/0x50 net/ipv6/af_inet6.c:476
__sock_release net/socket.c:650 [inline]
sock_close+0x6c/0x150 net/socket.c:1318
__fput+0x295/0x520 fs/file_table.c:280
____fput+0x11/0x20 fs/file_table.c:313
task_work_run+0x8e/0x110 kernel/task_work.c:164
tracehook_notify_resume include/linux/tracehook.h:189 [inline]
exit_to_user_mode_loop kernel/entry/common.c:175 [inline]
exit_to_user_mode_prepare+0x160/0x190 kernel/entry/common.c:207
__syscall_exit_to_user_mode_work kernel/entry/common.c:289 [inline]
syscall_exit_to_user_mode+0x20/0x40 kernel/entry/common.c:300
do_syscall_64+0x50/0xd0 arch/x86/entry/common.c:86
entry_SYSCALL_64_after_hwframe+0x44/0xae

write to 0xffff8881087d5886 of 1 bytes by task 1912 on cpu 1:
fib6_info_hw_flags_set+0x155/0x3b0 net/ipv6/route.c:6230
nsim_fib6_rt_hw_flags_set drivers/net/netdevsim/fib.c:668 [inline]
nsim_fib6_rt_add drivers/net/netdevsim/fib.c:691 [inline]
nsim_fib6_rt_insert drivers/net/netdevsim/fib.c:756 [inline]
nsim_fib6_event drivers/net/netdevsim/fib.c:853 [inline]
nsim_fib_event drivers/net/netdevsim/fib.c:886 [inline]
nsim_fib_event_work+0x284f/0x2cf0 drivers/net/netdevsim/fib.c:1477
process_one_work+0x3f6/0x960 kernel/workqueue.c:2307
worker_thread+0x616/0xa70 kernel/workqueue.c:2454
kthread+0x2c7/0x2e0 kernel/kthread.c:327
ret_from_fork+0x1f/0x30

value changed: 0x22 -> 0x2a

Reported by Kernel Concurrency Sanitizer on:
CPU: 1 PID: 1912 Comm: kworker/1:3 Not tainted 5.16.0-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events nsim_fib_event_work

Fixes: 0c5fcf9e249e ("IPv6: Add "offload failed" indication to routes")
Fixes: bb3c4ab93e44 ("ipv6: Add "offload" and "trap" indications to routes")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Amit Cohen <amcohen@nvidia.com>
Cc: Ido Schimmel <idosch@nvidia.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Link: https://lore.kernel.org/r/20220216173217.3792411-2-eric.dumazet@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
drivers/net/netdevsim/fib.c | 4 ++--
include/net/ip6_fib.h | 10 ++++++----
net/ipv6/route.c | 19 ++++++++++---------
3 files changed, 18 insertions(+), 15 deletions(-)

--- a/drivers/net/netdevsim/fib.c
+++ b/drivers/net/netdevsim/fib.c
@@ -623,14 +623,14 @@ static int nsim_fib6_rt_append(struct ns
if (err)
goto err_fib6_rt_nh_del;

- fib6_event->rt_arr[i]->trap = true;
+ WRITE_ONCE(fib6_event->rt_arr[i]->trap, true);
}

return 0;

err_fib6_rt_nh_del:
for (i--; i >= 0; i--) {
- fib6_event->rt_arr[i]->trap = false;
+ WRITE_ONCE(fib6_event->rt_arr[i]->trap, false);
nsim_fib6_rt_nh_del(fib6_rt, fib6_event->rt_arr[i]);
}
return err;
--- a/include/net/ip6_fib.h
+++ b/include/net/ip6_fib.h
@@ -189,14 +189,16 @@ struct fib6_info {
u32 fib6_metric;
u8 fib6_protocol;
u8 fib6_type;
+
+ u8 offload;
+ u8 trap;
+ u8 offload_failed;
+
u8 should_flush:1,
dst_nocount:1,
dst_nopolicy:1,
fib6_destroying:1,
- offload:1,
- trap:1,
- offload_failed:1,
- unused:1;
+ unused:4;

struct rcu_head rcu;
struct nexthop *nh;
--- a/net/ipv6/route.c
+++ b/net/ipv6/route.c
@@ -5767,11 +5767,11 @@ static int rt6_fill_node(struct net *net
}

if (!dst) {
- if (rt->offload)
+ if (READ_ONCE(rt->offload))
rtm->rtm_flags |= RTM_F_OFFLOAD;
- if (rt->trap)
+ if (READ_ONCE(rt->trap))
rtm->rtm_flags |= RTM_F_TRAP;
- if (rt->offload_failed)
+ if (READ_ONCE(rt->offload_failed))
rtm->rtm_flags |= RTM_F_OFFLOAD_FAILED;
}

@@ -6229,19 +6229,20 @@ void fib6_info_hw_flags_set(struct net *
struct sk_buff *skb;
int err;

- if (f6i->offload == offload && f6i->trap == trap &&
- f6i->offload_failed == offload_failed)
+ if (READ_ONCE(f6i->offload) == offload &&
+ READ_ONCE(f6i->trap) == trap &&
+ READ_ONCE(f6i->offload_failed) == offload_failed)
return;

- f6i->offload = offload;
- f6i->trap = trap;
+ WRITE_ONCE(f6i->offload, offload);
+ WRITE_ONCE(f6i->trap, trap);

/* 2 means send notifications only if offload_failed was changed. */
if (net->ipv6.sysctl.fib_notify_on_flag_change == 2 &&
- f6i->offload_failed == offload_failed)
+ READ_ONCE(f6i->offload_failed) == offload_failed)
return;

- f6i->offload_failed = offload_failed;
+ WRITE_ONCE(f6i->offload_failed, offload_failed);

if (!rcu_access_pointer(f6i->fib6_node))
/* The route was removed from the tree, do not send