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Subject[PATCH] ipv4: fix a RCU-list bug in inet_dump_fib()
Date
There is a place,

inet_dump_fib()
fib_table_dump
fn_trie_dump_leaf()
hlist_for_each_entry_rcu()

without rcu_read_lock() triggers a warning,

WARNING: suspicious RCU usage
-----------------------------
net/ipv4/fib_trie.c:2216 RCU-list traversed in non-reader section!!

other info that might help us debug this:

rcu_scheduler_active = 2, debug_locks = 1
1 lock held by ip/1923:
#0: ffffffff8ce76e40 (rtnl_mutex){+.+.}, at: netlink_dump+0xd6/0x840

Call Trace:
dump_stack+0xa1/0xea
lockdep_rcu_suspicious+0x103/0x10d
fn_trie_dump_leaf+0x581/0x590
fib_table_dump+0x15f/0x220
inet_dump_fib+0x4ad/0x5d0
netlink_dump+0x350/0x840
__netlink_dump_start+0x315/0x3e0
rtnetlink_rcv_msg+0x4d1/0x720
netlink_rcv_skb+0xf0/0x220
rtnetlink_rcv+0x15/0x20
netlink_unicast+0x306/0x460
netlink_sendmsg+0x44b/0x770
__sys_sendto+0x259/0x270
__x64_sys_sendto+0x80/0xa0
do_syscall_64+0x69/0xf4
entry_SYSCALL_64_after_hwframe+0x49/0xb3

Signed-off-by: Qian Cai <cai@lca.pw>
---
net/ipv4/fib_frontend.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/ipv4/fib_frontend.c b/net/ipv4/fib_frontend.c
index 577db1d50a24..5e441282d647 100644
--- a/net/ipv4/fib_frontend.c
+++ b/net/ipv4/fib_frontend.c
@@ -987,6 +987,8 @@ static int inet_dump_fib(struct sk_buff *skb, struct netlink_callback *cb)
if (filter.flags & RTM_F_PREFIX)
return skb->len;

+ rcu_read_lock();
+
if (filter.table_id) {
tb = fib_get_table(net, filter.table_id);
if (!tb) {
@@ -1004,8 +1006,6 @@ static int inet_dump_fib(struct sk_buff *skb, struct netlink_callback *cb)
s_h = cb->args[0];
s_e = cb->args[1];

- rcu_read_lock();
-
for (h = s_h; h < FIB_TABLE_HASHSZ; h++, s_e = 0) {
e = 0;
head = &net->ipv4.fib_table_hash[h];
--
2.21.0 (Apple Git-122.2)
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