[PATCH 5.0 017/117] net/sched: act_sample: fix divide by zero in the traffic path

Greg Kroah-Hartman
2019-04-15T19:19:32Z

[ Upstream commit fae2708174ae95d98d19f194e03d6e8f688ae195 ]

the control path of 'sample' action does not validate the value of 'rate'
provided by the user, but then it uses it as divisor in the traffic path.
Validate it in tcf_sample_init(), and return -EINVAL with a proper extack
message in case that value is zero, to fix a splat with the script below:

# tc f a dev test0 egress matchall action sample rate 0 group 1 index 2
# tc -s a s action sample
total acts 1

action order 0: sample rate 1/0 group 1 pipe
index 2 ref 1 bind 1 installed 19 sec used 19 sec
Action statistics:
Sent 0 bytes 0 pkt (dropped 0, overlimits 0 requeues 0)
backlog 0b 0p requeues 0
# ping 192.0.2.1 -I test0 -c1 -q

divide error: 0000 [#1] SMP PTI
CPU: 1 PID: 6192 Comm: ping Not tainted 5.1.0-rc2.diag2+ #591
Hardware name: Red Hat KVM, BIOS 0.5.1 01/01/2011
RIP: 0010:tcf_sample_act+0x9e/0x1e0 [act_sample]
Code: 6a f1 85 c0 74 0d 80 3d 83 1a 00 00 00 0f 84 9c 00 00 00 4d 85 e4 0f 84 85 00 00 00 e8 9b d7 9c f1 44 8b 8b e0 00 00 00 31 d2 <41> f7 f1 85 d2 75 70 f6 85 83 00 00 00 10 48 8b 45 10 8b 88 08 01
RSP: 0018:ffffae320190ba30 EFLAGS: 00010246
RAX: 00000000b0677d21 RBX: ffff8af1ed9ec000 RCX: 0000000059a9fe49
RDX: 0000000000000000 RSI: 000000000c7e33b7 RDI: ffff8af23daa0af0
RBP: ffff8af1ee11b200 R08: 0000000074fcaf7e R09: 0000000000000000
R10: 0000000000000050 R11: ffffffffb3088680 R12: ffff8af232307f80
R13: 0000000000000003 R14: ffff8af1ed9ec000 R15: 0000000000000000
FS: 00007fe9c6d2f740(0000) GS:ffff8af23da80000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fff6772f000 CR3: 00000000746a2004 CR4: 00000000001606e0
Call Trace:
tcf_action_exec+0x7c/0x1c0
tcf_classify+0x57/0x160
__dev_queue_xmit+0x3dc/0xd10
ip_finish_output2+0x257/0x6d0
ip_output+0x75/0x280
ip_send_skb+0x15/0x40
raw_sendmsg+0xae3/0x1410
sock_sendmsg+0x36/0x40
__sys_sendto+0x10e/0x140
__x64_sys_sendto+0x24/0x30
do_syscall_64+0x60/0x210
entry_SYSCALL_64_after_hwframe+0x49/0xbe
[...]
Kernel panic - not syncing: Fatal exception in interrupt

Add a TDC selftest to document that 'rate' is now being validated.

Reported-by: Matteo Croce <mcroce@redhat.com>
Fixes: 5c5670fae430 ("net/sched: Introduce sample tc action")
Signed-off-by: Davide Caratti <dcaratti@redhat.com>
Acked-by: Yotam Gigi <yotam.gi@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/sched/act_sample.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/net/sched/act_sample.c b/net/sched/act_sample.c
index 1a0c682fd734..fd62fe6c8e73 100644
--- a/net/sched/act_sample.c
+++ b/net/sched/act_sample.c
@@ -43,8 +43,8 @@ static int tcf_sample_init(struct net *net, struct nlattr *nla,
struct tc_action_net *tn = net_generic(net, sample_net_id);
struct nlattr *tb[TCA_SAMPLE_MAX + 1];
struct psample_group *psample_group;
+ u32 psample_group_num, rate;
struct tc_sample *parm;
- u32 psample_group_num;
struct tcf_sample *s;
bool exists = false;
int ret, err;
@@ -80,6 +80,12 @@ static int tcf_sample_init(struct net *net, struct nlattr *nla,
return -EEXIST;
}

+ rate = nla_get_u32(tb[TCA_SAMPLE_RATE]);
+ if (!rate) {
+ NL_SET_ERR_MSG(extack, "invalid sample rate");
+ tcf_idr_release(*a, bind);
+ return -EINVAL;
+ }
psample_group_num = nla_get_u32(tb[TCA_SAMPLE_PSAMPLE_GROUP]);
psample_group = psample_group_get(net, psample_group_num);
if (!psample_group) {
@@ -91,7 +97,7 @@ static int tcf_sample_init(struct net *net, struct nlattr *nla,

spin_lock_bh(&s->tcf_lock);
s->tcf_action = parm->action;
- s->rate = nla_get_u32(tb[TCA_SAMPLE_RATE]);
+ s->rate = rate;
s->psample_group_num = psample_group_num;
RCU_INIT_POINTER(s->psample_group, psample_group);

--
2.19.1