WARNING in xfrm_policy_inexact_list_reinsert

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: 4010b622 Merge branch 'dax-fix-5.3-rc3' of git://git.kerne..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13e2829fa00000
kernel config: https://syzkaller.appspot.com/x/.config?x=e397351d2615e10
dashboard link: https://syzkaller.appspot.com/bug?extid=8cc27ace5f6972910b31
compiler: clang version 9.0.0 (/home/glider/llvm/clang
80fee25776c2fb61e74c1ecb1a523375c2500b69)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+8cc27a...@syzkaller.appspotmail.com

WARNING: CPU: 1 PID: 6756 at net/xfrm/xfrm_policy.c:877
xfrm_policy_inexact_list_reinsert+0x625/0x6e0 net/xfrm/xfrm_policy.c:877
Kernel panic - not syncing: panic_on_warn set ...
CPU: 1 PID: 6756 Comm: syz-executor.1 Not tainted 5.3.0-rc2+ #57
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Call Trace:
__dump_stack lib/dump_stack.c:77 [inline]
dump_stack+0x1d8/0x2f8 lib/dump_stack.c:113
panic+0x29b/0x7d9 kernel/panic.c:219
__warn+0x22f/0x230 kernel/panic.c:576
report_bug+0x190/0x290 lib/bug.c:186
fixup_bug arch/x86/kernel/traps.c:179 [inline]
do_error_trap+0xd7/0x440 arch/x86/kernel/traps.c:272
do_invalid_op+0x36/0x40 arch/x86/kernel/traps.c:291
invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1026
RIP: 0010:xfrm_policy_inexact_list_reinsert+0x625/0x6e0
net/xfrm/xfrm_policy.c:877
Code: ef e8 6f 32 0f fb 4d 8b 6d 00 4c 39 6d 90 0f 85 81 fa ff ff e9 b0 00
00 00 e8 c7 87 d4 fa 0f 0b e9 fa fa ff ff e8 bb 87 d4 fa <0f> 0b e9 75 ff
ff ff e8 af 87 d4 fa 0f 0b eb a9 44 89 f1 80 e1 07
RSP: 0018:ffff888052caf080 EFLAGS: 00010283
RAX: ffffffff86a35975 RBX: 00000000ffffff20 RCX: 0000000000040000
RDX: ffffc9000816a000 RSI: 00000000000005cd RDI: 00000000000005ce
RBP: ffff888052caf110 R08: ffffffff86a358ac R09: ffffffff86a3514c
R10: ffff88805914c380 R11: 0000000000000002 R12: 0000000000000000
R13: ffff888092fa6aa0 R14: 000000000000007e R15: 000000000000000a
xfrm_policy_inexact_node_reinsert net/xfrm/xfrm_policy.c:922 [inline]
xfrm_policy_inexact_node_merge net/xfrm/xfrm_policy.c:958 [inline]
xfrm_policy_inexact_insert_node+0x537/0xb50 net/xfrm/xfrm_policy.c:1023
xfrm_policy_inexact_alloc_chain+0x62b/0xbd0 net/xfrm/xfrm_policy.c:1139
xfrm_policy_inexact_insert+0xe8/0x1540 net/xfrm/xfrm_policy.c:1182
xfrm_policy_insert+0xdf/0xce0 net/xfrm/xfrm_policy.c:1574
xfrm_add_policy+0x4cf/0x9b0 net/xfrm/xfrm_user.c:1670
xfrm_user_rcv_msg+0x46b/0x720 net/xfrm/xfrm_user.c:2676
netlink_rcv_skb+0x1f0/0x460 net/netlink/af_netlink.c:2477
xfrm_netlink_rcv+0x74/0x90 net/xfrm/xfrm_user.c:2684
netlink_unicast_kernel net/netlink/af_netlink.c:1302 [inline]
netlink_unicast+0x809/0x9a0 net/netlink/af_netlink.c:1328
netlink_sendmsg+0xa70/0xd30 net/netlink/af_netlink.c:1917
sock_sendmsg_nosec net/socket.c:637 [inline]
sock_sendmsg net/socket.c:657 [inline]
___sys_sendmsg+0x66b/0x9a0 net/socket.c:2311
__sys_sendmsg net/socket.c:2356 [inline]
__do_sys_sendmsg net/socket.c:2365 [inline]
__se_sys_sendmsg net/socket.c:2363 [inline]
__x64_sys_sendmsg+0x1cf/0x290 net/socket.c:2363
do_syscall_64+0xfe/0x140 arch/x86/entry/common.c:296
entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x459829
Code: fd b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 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 0f 83 cb b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f16cc51ec78 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 0000000000459829
RDX: 0000000000000000 RSI: 0000000020000080 RDI: 0000000000000003
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f16cc51f6d4
R13: 00000000004c776b R14: 00000000004dceb8 R15: 00000000ffffffff
Kernel Offset: disabled
Rebooting in 86400 seconds..


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[Florian Westphal]

syzbot reported a splat:
xfrm_policy_inexact_list_reinsert+0x625/0x6e0 net/xfrm/xfrm_policy.c:877

CPU: 1 PID: 6756 Comm: syz-executor.1 Not tainted 5.3.0-rc2+ #57

Call Trace:

xfrm_policy_inexact_node_reinsert net/xfrm/xfrm_policy.c:922 [inline]
xfrm_policy_inexact_node_merge net/xfrm/xfrm_policy.c:958 [inline]
xfrm_policy_inexact_insert_node+0x537/0xb50 net/xfrm/xfrm_policy.c:1023
xfrm_policy_inexact_alloc_chain+0x62b/0xbd0 net/xfrm/xfrm_policy.c:1139
xfrm_policy_inexact_insert+0xe8/0x1540 net/xfrm/xfrm_policy.c:1182
xfrm_policy_insert+0xdf/0xce0 net/xfrm/xfrm_policy.c:1574
xfrm_add_policy+0x4cf/0x9b0 net/xfrm/xfrm_user.c:1670
xfrm_user_rcv_msg+0x46b/0x720 net/xfrm/xfrm_user.c:2676
netlink_rcv_skb+0x1f0/0x460 net/netlink/af_netlink.c:2477
xfrm_netlink_rcv+0x74/0x90 net/xfrm/xfrm_user.c:2684
netlink_unicast_kernel net/netlink/af_netlink.c:1302 [inline]
netlink_unicast+0x809/0x9a0 net/netlink/af_netlink.c:1328
netlink_sendmsg+0xa70/0xd30 net/netlink/af_netlink.c:1917
sock_sendmsg_nosec net/socket.c:637 [inline]
sock_sendmsg net/socket.c:657 [inline]

There is no reproducer, however, the warning can be reproduced
by adding rules with ever smaller prefixes.

The sanity check ("does the policy match the node") uses the prefix value
of the node before its updated to the smaller value.

To fix this, update the prefix earlier. The bug has no impact on tree
correctness, this is only to prevent a false warning.

Reported-by: syzbot+8cc27a...@syzkaller.appspotmail.com
Signed-off-by: Florian Westphal <f...@strlen.de>
---
net/xfrm/xfrm_policy.c | 6 ++++--
tools/testing/selftests/net/xfrm_policy.sh | 7 +++++++
2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/net/xfrm/xfrm_policy.c b/net/xfrm/xfrm_policy.c
index 8ca637a72697..0fa7c5ce3b2c 100644
--- a/net/xfrm/xfrm_policy.c
+++ b/net/xfrm/xfrm_policy.c
@@ -912,6 +912,7 @@ static void xfrm_policy_inexact_node_reinsert(struct net *net,
} else if (delta > 0) {
p = &parent->rb_right;
} else {
+ bool same_prefixlen = node->prefixlen == n->prefixlen;
struct xfrm_policy *tmp;

hlist_for_each_entry(tmp, &n->hhead, bydst) {
@@ -919,9 +920,11 @@ static void xfrm_policy_inexact_node_reinsert(struct net *net,
hlist_del_rcu(&tmp->bydst);
}

+ node->prefixlen = prefixlen;
+
xfrm_policy_inexact_list_reinsert(net, node, family);

- if (node->prefixlen == n->prefixlen) {
+ if (same_prefixlen) {
kfree_rcu(n, rcu);
return;
}
@@ -929,7 +932,6 @@ static void xfrm_policy_inexact_node_reinsert(struct net *net,
rb_erase(*p, new);
kfree_rcu(n, rcu);
n = node;
- n->prefixlen = prefixlen;
goto restart;
}
}
diff --git a/tools/testing/selftests/net/xfrm_policy.sh b/tools/testing/selftests/net/xfrm_policy.sh
index 5445943bf07f..7a1bf94c5bd3 100755
--- a/tools/testing/selftests/net/xfrm_policy.sh
+++ b/tools/testing/selftests/net/xfrm_policy.sh
@@ -106,6 +106,13 @@ do_overlap()
#
# 10.0.0.0/24 and 10.0.1.0/24 nodes have been merged as 10.0.0.0/23.
ip -net $ns xfrm policy add src 10.1.0.0/24 dst 10.0.0.0/23 dir fwd priority 200 action block
+
+ # similar to above: add policies (with partially random address), with shrinking prefixes.
+ for p in 29 28 27;do
+ for k in $(seq 1 32); do
+ ip -net $ns xfrm policy add src 10.253.1.$((RANDOM%255))/$p dst 10.254.1.$((RANDOM%255))/$p dir fwd priority $((200+k)) action block 2>/dev/null
+ done
+ done
}

do_esp_policy_get_check() {
--
2.21.0

[Steffen Klassert]

Applied, thanks Florian!