net/sched: flower: fix fl_change() error recovery path

The two "goto errout;" paths in fl_change() became wrong
after cited commit.

Indeed we only must not call __fl_put() until the net pointer
has been set in tcf_exts_init_ex()

This is a minimal fix. We might in the future validate TCA_FLOWER_FLAGS
before we allocate @fnew.

BUG: KASAN: null-ptr-deref in instrument_atomic_read include/linux/instrumented.h:72 [inline]
BUG: KASAN: null-ptr-deref in atomic_read include/linux/atomic/atomic-instrumented.h:27 [inline]
BUG: KASAN: null-ptr-deref in refcount_read include/linux/refcount.h:147 [inline]
BUG: KASAN: null-ptr-deref in __refcount_add_not_zero include/linux/refcount.h:152 [inline]
BUG: KASAN: null-ptr-deref in __refcount_inc_not_zero include/linux/refcount.h:227 [inline]
BUG: KASAN: null-ptr-deref in refcount_inc_not_zero include/linux/refcount.h:245 [inline]
BUG: KASAN: null-ptr-deref in maybe_get_net include/net/net_namespace.h:269 [inline]
BUG: KASAN: null-ptr-deref in tcf_exts_get_net include/net/pkt_cls.h:260 [inline]
BUG: KASAN: null-ptr-deref in __fl_put net/sched/cls_flower.c:513 [inline]
BUG: KASAN: null-ptr-deref in __fl_put+0x13e/0x3b0 net/sched/cls_flower.c:508
Read of size 4 at addr 000000000000014c by task syz-executor548/5082

CPU: 0 PID: 5082 Comm: syz-executor548 Not tainted 6.2.0-syzkaller-05251-g5b7c4cabbb65 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/21/2023
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0xd9/0x150 lib/dump_stack.c:106
print_report mm/kasan/report.c:420 [inline]
kasan_report+0xec/0x130 mm/kasan/report.c:517
check_region_inline mm/kasan/generic.c:183 [inline]
kasan_check_range+0x141/0x190 mm/kasan/generic.c:189
instrument_atomic_read include/linux/instrumented.h:72 [inline]
atomic_read include/linux/atomic/atomic-instrumented.h:27 [inline]
refcount_read include/linux/refcount.h:147 [inline]
__refcount_add_not_zero include/linux/refcount.h:152 [inline]
__refcount_inc_not_zero include/linux/refcount.h:227 [inline]
refcount_inc_not_zero include/linux/refcount.h:245 [inline]
maybe_get_net include/net/net_namespace.h:269 [inline]
tcf_exts_get_net include/net/pkt_cls.h:260 [inline]
__fl_put net/sched/cls_flower.c:513 [inline]
__fl_put+0x13e/0x3b0 net/sched/cls_flower.c:508
fl_change+0x101b/0x4ab0 net/sched/cls_flower.c:2341
tc_new_tfilter+0x97c/0x2290 net/sched/cls_api.c:2310
rtnetlink_rcv_msg+0x996/0xd50 net/core/rtnetlink.c:6165
netlink_rcv_skb+0x165/0x440 net/netlink/af_netlink.c:2574
netlink_unicast_kernel net/netlink/af_netlink.c:1339 [inline]
netlink_unicast+0x547/0x7f0 net/netlink/af_netlink.c:1365
netlink_sendmsg+0x925/0xe30 net/netlink/af_netlink.c:1942
sock_sendmsg_nosec net/socket.c:722 [inline]
sock_sendmsg+0xde/0x190 net/socket.c:745
____sys_sendmsg+0x334/0x900 net/socket.c:2504
___sys_sendmsg+0x110/0x1b0 net/socket.c:2558
__sys_sendmmsg+0x18f/0x460 net/socket.c:2644
__do_sys_sendmmsg net/socket.c:2673 [inline]
__se_sys_sendmmsg net/socket.c:2670 [inline]
__x64_sys_sendmmsg+0x9d/0x100 net/socket.c:2670

Fixes: 08a0063df3 ("net/sched: flower: Move filter handle initialization earlier")
Reported-by: syzbot+baabf3efa7c1e57d28b2@syzkaller.appspotmail.com
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Paul Blakey <paulb@nvidia.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/sched/cls_flower.c

@@ -2200,8 +2200,9 @@ static int fl_change(struct net *net, struct sk_buff *in_skb,
 		fnew->flags = nla_get_u32(tb[TCA_FLOWER_FLAGS]);
 
 		if (!tc_flags_valid(fnew->flags)) {
+			kfree(fnew);
 			err = -EINVAL;
-			goto errout;
+			goto errout_tb;
 		}
 	}
 
@@ -2226,8 +2227,10 @@ static int fl_change(struct net *net, struct sk_buff *in_skb,
 		}
 		spin_unlock(&tp->lock);
 
-		if (err)
-			goto errout;
+		if (err) {
+			kfree(fnew);
+			goto errout_tb;
+		}
 	}
 	fnew->handle = handle;
 
@@ -2337,7 +2340,6 @@ errout_mask:
 	fl_mask_put(head, fnew->mask);
 errout_idr:
 	idr_remove(&head->handle_idr, fnew->handle);
-errout:
 	__fl_put(fnew);
 errout_tb:
 	kfree(tb);