[PATCH 5.16 101/227] ipv4: fix data races in fib_alias_hw_flags_set

Greg Kroah-Hartman
2022-02-21T09:52:33Z

From: Eric Dumazet <edumazet@google.com>

commit 9fcf986cc4bc6a3a39f23fbcbbc3a9e52d3c24fd upstream.

fib_alias_hw_flags_set() can be used by concurrent threads,
and is only RCU protected.

We need to annotate accesses to following fields of struct fib_alias:

offload, trap, offload_failed

Because of READ_ONCE()WRITE_ONCE() limitations, make these
field u8.

BUG: KCSAN: data-race in fib_alias_hw_flags_set / fib_alias_hw_flags_set

read to 0xffff888134224a6a of 1 bytes by task 2013 on cpu 1:
fib_alias_hw_flags_set+0x28a/0x470 net/ipv4/fib_trie.c:1050
nsim_fib4_rt_hw_flags_set drivers/net/netdevsim/fib.c:350 [inline]
nsim_fib4_rt_add drivers/net/netdevsim/fib.c:367 [inline]
nsim_fib4_rt_insert drivers/net/netdevsim/fib.c:429 [inline]
nsim_fib4_event drivers/net/netdevsim/fib.c:461 [inline]
nsim_fib_event drivers/net/netdevsim/fib.c:881 [inline]
nsim_fib_event_work+0x1852/0x2cf0 drivers/net/netdevsim/fib.c:1477
process_one_work+0x3f6/0x960 kernel/workqueue.c:2307
process_scheduled_works kernel/workqueue.c:2370 [inline]
worker_thread+0x7df/0xa70 kernel/workqueue.c:2456
kthread+0x1bf/0x1e0 kernel/kthread.c:377
ret_from_fork+0x1f/0x30

write to 0xffff888134224a6a of 1 bytes by task 4872 on cpu 0:
fib_alias_hw_flags_set+0x2d5/0x470 net/ipv4/fib_trie.c:1054
nsim_fib4_rt_hw_flags_set drivers/net/netdevsim/fib.c:350 [inline]
nsim_fib4_rt_add drivers/net/netdevsim/fib.c:367 [inline]
nsim_fib4_rt_insert drivers/net/netdevsim/fib.c:429 [inline]
nsim_fib4_event drivers/net/netdevsim/fib.c:461 [inline]
nsim_fib_event drivers/net/netdevsim/fib.c:881 [inline]
nsim_fib_event_work+0x1852/0x2cf0 drivers/net/netdevsim/fib.c:1477
process_one_work+0x3f6/0x960 kernel/workqueue.c:2307
process_scheduled_works kernel/workqueue.c:2370 [inline]
worker_thread+0x7df/0xa70 kernel/workqueue.c:2456
kthread+0x1bf/0x1e0 kernel/kthread.c:377
ret_from_fork+0x1f/0x30

value changed: 0x00 -> 0x02

Reported by Kernel Concurrency Sanitizer on:
CPU: 0 PID: 4872 Comm: kworker/0:0 Not tainted 5.17.0-rc3-syzkaller-00188-g1d41d2e82623-dirty #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events nsim_fib_event_work

Fixes: 90b93f1b31f8 ("ipv4: Add "offload" and "trap" indications to routes")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: syzbot <syzkaller@googlegroups.com>
Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Link: https://lore.kernel.org/r/20220216173217.3792411-1-eric.dumazet@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/ipv4/fib_lookup.h | 7 +++----
net/ipv4/fib_semantics.c | 6 +++---
net/ipv4/fib_trie.c | 22 +++++++++++++---------
net/ipv4/route.c | 4 ++--
4 files changed, 21 insertions(+), 18 deletions(-)

--- a/net/ipv4/fib_lookup.h
+++ b/net/ipv4/fib_lookup.h
@@ -16,10 +16,9 @@ struct fib_alias {
u8 fa_slen;
u32 tb_id;
s16 fa_default;
- u8 offload:1,
- trap:1,
- offload_failed:1,
- unused:5;
+ u8 offload;
+ u8 trap;
+ u8 offload_failed;
struct rcu_head rcu;
};

--- a/net/ipv4/fib_semantics.c
+++ b/net/ipv4/fib_semantics.c
@@ -524,9 +524,9 @@ void rtmsg_fib(int event, __be32 key, st
fri.dst_len = dst_len;
fri.tos = fa->fa_tos;
fri.type = fa->fa_type;
- fri.offload = fa->offload;
- fri.trap = fa->trap;
- fri.offload_failed = fa->offload_failed;
+ fri.offload = READ_ONCE(fa->offload);
+ fri.trap = READ_ONCE(fa->trap);
+ fri.offload_failed = READ_ONCE(fa->offload_failed);
err = fib_dump_info(skb, info->portid, seq, event, &fri, nlm_flags);
if (err < 0) {
/* -EMSGSIZE implies BUG in fib_nlmsg_size() */
--- a/net/ipv4/fib_trie.c
+++ b/net/ipv4/fib_trie.c
@@ -1047,19 +1047,23 @@ void fib_alias_hw_flags_set(struct net *
if (!fa_match)
goto out;

- if (fa_match->offload == fri->offload && fa_match->trap == fri->trap &&
- fa_match->offload_failed == fri->offload_failed)
+ /* These are paired with the WRITE_ONCE() happening in this function.
+ * The reason is that we are only protected by RCU at this point.
+ */
+ if (READ_ONCE(fa_match->offload) == fri->offload &&
+ READ_ONCE(fa_match->trap) == fri->trap &&
+ READ_ONCE(fa_match->offload_failed) == fri->offload_failed)
goto out;

- fa_match->offload = fri->offload;
- fa_match->trap = fri->trap;
+ WRITE_ONCE(fa_match->offload, fri->offload);
+ WRITE_ONCE(fa_match->trap, fri->trap);

/* 2 means send notifications only if offload_failed was changed. */
if (net->ipv4.sysctl_fib_notify_on_flag_change == 2 &&
- fa_match->offload_failed == fri->offload_failed)
+ READ_ONCE(fa_match->offload_failed) == fri->offload_failed)
goto out;

- fa_match->offload_failed = fri->offload_failed;
+ WRITE_ONCE(fa_match->offload_failed, fri->offload_failed);

if (!net->ipv4.sysctl_fib_notify_on_flag_change)
goto out;
@@ -2297,9 +2301,9 @@ static int fn_trie_dump_leaf(struct key_
fri.dst_len = KEYLENGTH - fa->fa_slen;
fri.tos = fa->fa_tos;
fri.type = fa->fa_type;
- fri.offload = fa->offload;
- fri.trap = fa->trap;
- fri.offload_failed = fa->offload_failed;
+ fri.offload = READ_ONCE(fa->offload);
+ fri.trap = READ_ONCE(fa->trap);
+ fri.offload_failed = READ_ONCE(fa->offload_failed);
err = fib_dump_info(skb,
NETLINK_CB(cb->skb).portid,
cb->nlh->nlmsg_seq,
--- a/net/ipv4/route.c
+++ b/net/ipv4/route.c
@@ -3393,8 +3393,8 @@ static int inet_rtm_getroute(struct sk_b
fa->fa_tos == fri.tos &&
fa->fa_info == res.fi &&
fa->fa_type == fri.type) {
- fri.offload = fa->offload;
- fri.trap = fa->trap;
+ fri.offload = READ_ONCE(fa->offload);
+ fri.trap = READ_ONCE(fa->trap);
break;
}
}