5.4-stable review patch. If anyone has any objections, please let me know.
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From: Kuniyuki Iwashima kuniyu@google.com
[ Upstream commit 6dbb0d97c5096072c78a6abffe393584e57ae945 ]
As syzbot reported [0], mpls_route_input_rcu() can be called from mpls_getroute(), where is under RTNL.
net->mpls.platform_label is only updated under RTNL.
Let's use rcu_dereference_rtnl() in mpls_route_input_rcu() to silence the splat.
[0]: WARNING: suspicious RCU usage 6.15.0-rc7-syzkaller-00082-g5cdb2c77c4c3 #0 Not tainted ---------------------------- net/mpls/af_mpls.c:84 suspicious rcu_dereference_check() usage!
other info that might help us debug this:
rcu_scheduler_active = 2, debug_locks = 1 1 lock held by syz.2.4451/17730: #0: ffffffff9012a3e8 (rtnl_mutex){+.+.}-{4:4}, at: rtnl_lock net/core/rtnetlink.c:80 [inline] #0: ffffffff9012a3e8 (rtnl_mutex){+.+.}-{4:4}, at: rtnetlink_rcv_msg+0x371/0xe90 net/core/rtnetlink.c:6961
stack backtrace: CPU: 1 UID: 0 PID: 17730 Comm: syz.2.4451 Not tainted 6.15.0-rc7-syzkaller-00082-g5cdb2c77c4c3 #0 PREEMPT(full) Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/07/2025 Call Trace: <TASK> __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0x16c/0x1f0 lib/dump_stack.c:120 lockdep_rcu_suspicious+0x166/0x260 kernel/locking/lockdep.c:6865 mpls_route_input_rcu+0x1d4/0x200 net/mpls/af_mpls.c:84 mpls_getroute+0x621/0x1ea0 net/mpls/af_mpls.c:2381 rtnetlink_rcv_msg+0x3c9/0xe90 net/core/rtnetlink.c:6964 netlink_rcv_skb+0x16d/0x440 net/netlink/af_netlink.c:2534 netlink_unicast_kernel net/netlink/af_netlink.c:1313 [inline] netlink_unicast+0x53a/0x7f0 net/netlink/af_netlink.c:1339 netlink_sendmsg+0x8d1/0xdd0 net/netlink/af_netlink.c:1883 sock_sendmsg_nosec net/socket.c:712 [inline] __sock_sendmsg net/socket.c:727 [inline] ____sys_sendmsg+0xa98/0xc70 net/socket.c:2566 ___sys_sendmsg+0x134/0x1d0 net/socket.c:2620 __sys_sendmmsg+0x200/0x420 net/socket.c:2709 __do_sys_sendmmsg net/socket.c:2736 [inline] __se_sys_sendmmsg net/socket.c:2733 [inline] __x64_sys_sendmmsg+0x9c/0x100 net/socket.c:2733 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xcd/0x230 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f0a2818e969 Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007f0a28f52038 EFLAGS: 00000246 ORIG_RAX: 0000000000000133 RAX: ffffffffffffffda RBX: 00007f0a283b5fa0 RCX: 00007f0a2818e969 RDX: 0000000000000003 RSI: 0000200000000080 RDI: 0000000000000003 RBP: 00007f0a28210ab1 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 0000000000000000 R14: 00007f0a283b5fa0 R15: 00007ffce5e9f268 </TASK>
Fixes: 0189197f4416 ("mpls: Basic routing support") Reported-by: syzbot+8a583bdd1a5cc0b0e068@syzkaller.appspotmail.com Closes: https://lore.kernel.org/netdev/68507981.a70a0220.395abc.01ef.GAE@google.com/ Signed-off-by: Kuniyuki Iwashima kuniyu@google.com Link: https://patch.msgid.link/20250616201532.1036568-1-kuni1840@gmail.com Signed-off-by: Jakub Kicinski kuba@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- net/mpls/af_mpls.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/net/mpls/af_mpls.c b/net/mpls/af_mpls.c index 3a55a392e0218..bac87a6b7e5b9 100644 --- a/net/mpls/af_mpls.c +++ b/net/mpls/af_mpls.c @@ -80,8 +80,8 @@ static struct mpls_route *mpls_route_input_rcu(struct net *net, unsigned index)
if (index < net->mpls.platform_labels) { struct mpls_route __rcu **platform_label = - rcu_dereference(net->mpls.platform_label); - rt = rcu_dereference(platform_label[index]); + rcu_dereference_rtnl(net->mpls.platform_label); + rt = rcu_dereference_rtnl(platform_label[index]); } return rt; }