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ipv4: fix data races in fib_alias_hw_flags_set
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commit 9fcf986 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: 90b93f1 ("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>
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@gregkh
Eric Dumazet authored and gregkh committed Feb 23, 2022
1 parent 5dc653e commit db33369
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Showing 4 changed files with 21 additions and 18 deletions.
7 changes: 3 additions & 4 deletions net/ipv4/fib_lookup.h
View file
Expand Up @@ -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;
};

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6 changes: 3 additions & 3 deletions net/ipv4/fib_semantics.c
View file
Expand Up @@ -524,9 +524,9 @@ void rtmsg_fib(int event, __be32 key, struct fib_alias *fa,
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() */
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22 changes: 13 additions & 9 deletions net/ipv4/fib_trie.c
View file
Expand Up @@ -1047,19 +1047,23 @@ void fib_alias_hw_flags_set(struct net *net, const struct fib_rt_info *fri)
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;
Expand Down Expand Up @@ -2297,9 +2301,9 @@ static int fn_trie_dump_leaf(struct key_vector *l, struct fib_table *tb,
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,
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4 changes: 2 additions & 2 deletions net/ipv4/route.c
View file
Expand Up @@ -3401,8 +3401,8 @@ static int inet_rtm_getroute(struct sk_buff *in_skb, struct nlmsghdr *nlh,
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;
}
}
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