From: Wei Wang <weiwan@xxxxxxxxxx>
[ Upstream commit 28259bac7f1dde06d8ba324e222bbec9d4e92f2b ]
Syzbot reported the suspecious RCU usage in nexthop_fib6_nh() when
called from ipv6_route_seq_show(). The reason is ipv6_route_seq_start()
calls rcu_read_lock_bh(), while nexthop_fib6_nh() calls
rcu_dereference_rtnl().
The fix proposed is to add a variant of nexthop_fib6_nh() to use
rcu_dereference_bh_rtnl() for ipv6_route_seq_show().
The reported trace is as follows:
./include/net/nexthop.h:416 suspicious rcu_dereference_check() usage!
other info that might help us debug this:
rcu_scheduler_active = 2, debug_locks = 1
2 locks held by syz-executor.0/17895:
at: seq_read+0x71/0x12a0 fs/seq_file.c:169
at: seq_file_net include/linux/seq_file_net.h:19 [inline]
at: ipv6_route_seq_start+0xaf/0x300 net/ipv6/ip6_fib.c:2616
stack backtrace:
CPU: 1 PID: 17895 Comm: syz-executor.0 Not tainted 4.15.0-syzkaller #0
Call Trace:
[<ffffffff849edf9e>] __dump_stack lib/dump_stack.c:17 [inline]
[<ffffffff849edf9e>] dump_stack+0xd8/0x147 lib/dump_stack.c:53
[<ffffffff8480b7fa>] lockdep_rcu_suspicious+0x153/0x15d kernel/locking/lockdep.c:5745
[<ffffffff8459ada6>] nexthop_fib6_nh include/net/nexthop.h:416 [inline]
[<ffffffff8459ada6>] ipv6_route_native_seq_show net/ipv6/ip6_fib.c:2488 [inline]
[<ffffffff8459ada6>] ipv6_route_seq_show+0x436/0x7a0 net/ipv6/ip6_fib.c:2673
[<ffffffff81c556df>] seq_read+0xccf/0x12a0 fs/seq_file.c:276
[<ffffffff81dbc62c>] proc_reg_read+0x10c/0x1d0 fs/proc/inode.c:231
[<ffffffff81bc28ae>] do_loop_readv_writev fs/read_write.c:714 [inline]
[<ffffffff81bc28ae>] do_loop_readv_writev fs/read_write.c:701 [inline]
[<ffffffff81bc28ae>] do_iter_read+0x49e/0x660 fs/read_write.c:935
[<ffffffff81bc81ab>] vfs_readv+0xfb/0x170 fs/read_write.c:997
[<ffffffff81c88847>] kernel_readv fs/splice.c:361 [inline]
[<ffffffff81c88847>] default_file_splice_read+0x487/0x9c0 fs/splice.c:416
[<ffffffff81c86189>] do_splice_to+0x129/0x190 fs/splice.c:879
[<ffffffff81c86f66>] splice_direct_to_actor+0x256/0x890 fs/splice.c:951
[<ffffffff81c8777d>] do_splice_direct+0x1dd/0x2b0 fs/splice.c:1060
[<ffffffff81bc4747>] do_sendfile+0x597/0xce0 fs/read_write.c:1459
[<ffffffff81bca205>] SYSC_sendfile64 fs/read_write.c:1520 [inline]
[<ffffffff81bca205>] SyS_sendfile64+0x155/0x170 fs/read_write.c:1506
[<ffffffff81015fcf>] do_syscall_64+0x1ff/0x310 arch/x86/entry/common.c:305
[<ffffffff84a00076>] entry_SYSCALL_64_after_hwframe+0x42/0xb7
Fixes: f88d8ea67fbdb ("ipv6: Plumb support for nexthop object in a fib6_info")
Reported-by: syzbot <syzkaller@xxxxxxxxxxxxxxxx>
Signed-off-by: Wei Wang <weiwan@xxxxxxxxxx>
Cc: David Ahern <dsahern@xxxxxxxxxx>
Cc: Ido Schimmel <idosch@xxxxxxxxxx>
Cc: Petr Machata <petrm@xxxxxxxxxx>
Cc: Eric Dumazet <edumazet@xxxxxxxxxx>
Reviewed-by: Ido Schimmel <idosch@xxxxxxxxxx>
Reviewed-by: David Ahern <dsahern@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
include/net/nexthop.h | 24 ++++++++++++++++++++++++
net/ipv6/ip6_fib.c | 2 +-
2 files changed, 25 insertions(+), 1 deletion(-)
diff --git a/include/net/nexthop.h b/include/net/nexthop.h
index 2fd76a9b6dc8..4c8c9fe9a3f0 100644
--- a/include/net/nexthop.h
+++ b/include/net/nexthop.h
@@ -362,6 +362,7 @@ static inline struct fib_nh *fib_info_nh(struct fib_info *fi, int nhsel)
int fib6_check_nexthop(struct nexthop *nh, struct fib6_config *cfg,
struct netlink_ext_ack *extack);
+/* Caller should either hold rcu_read_lock(), or RTNL. */
static inline struct fib6_nh *nexthop_fib6_nh(struct nexthop *nh)
{
struct nh_info *nhi;
@@ -382,6 +383,29 @@ static inline struct fib6_nh *nexthop_fib6_nh(struct nexthop *nh)
return NULL;
}
+/* Variant of nexthop_fib6_nh().
+ * Caller should either hold rcu_read_lock_bh(), or RTNL.
+ */
+static inline struct fib6_nh *nexthop_fib6_nh_bh(struct nexthop *nh)
+{
+ struct nh_info *nhi;
+
+ if (nh->is_group) {
+ struct nh_group *nh_grp;
+
+ nh_grp = rcu_dereference_bh_rtnl(nh->nh_grp);
+ nh = nexthop_mpath_select(nh_grp, 0);
+ if (!nh)
+ return NULL;
+ }
+
+ nhi = rcu_dereference_bh_rtnl(nh->nh_info);
+ if (nhi->family == AF_INET6)
+ return &nhi->fib6_nh;
+
+ return NULL;
+}
+
static inline struct net_device *fib6_info_nh_dev(struct fib6_info *f6i)
{
struct fib6_nh *fib6_nh;
diff --git a/net/ipv6/ip6_fib.c b/net/ipv6/ip6_fib.c
index f43e27555725..1fb79dbde0cb 100644
--- a/net/ipv6/ip6_fib.c
+++ b/net/ipv6/ip6_fib.c
@@ -2485,7 +2485,7 @@ static int ipv6_route_native_seq_show(struct seq_file *seq, void *v)
const struct net_device *dev;
if (rt->nh)
- fib6_nh = nexthop_fib6_nh(rt->nh);
+ fib6_nh = nexthop_fib6_nh_bh(rt->nh);
seq_printf(seq, "%pi6 %02x ", &rt->fib6_dst.addr, rt->fib6_dst.plen);
--
2.30.1
