[PATCH 5.3 114/135] net: psample: fix skb_over_panic

From: Greg Kroah-Hartman
Date: Tue Dec 03 2019 - 17:44:09 EST

From: Nikolay Aleksandrov <nikolay@xxxxxxxxxxxxxxxxxxx>

[ Upstream commit 7eb9d7675c08937cd11d32b0b40442d4d731c5ee ]

We need to calculate the skb size correctly otherwise we risk triggering
skb_over_panic[1]. The issue is that data_len is added to the skb in a
nl attribute, but we don't account for its header size (nlattr 4 bytes)
and alignment. We account for it when calculating the total size in
the > PSAMPLE_MAX_PACKET_SIZE comparison correctly, but not when
allocating after that. The fix is simple - use nla_total_size() for
data_len when allocating.

To reproduce:
$ tc qdisc add dev eth1 clsact
$ tc filter add dev eth1 egress matchall action sample rate 1 group 1 trunc 129
$ mausezahn eth1 -b bcast -a rand -c 1 -p 129
< skb_over_panic BUG(), tail is 4 bytes past skb->end >

[1] Trace:
[ 50.459526][ T3480] skbuff: skb_over_panic: text:(____ptrval____) len:196 put:136 head:(____ptrval____) data:(____ptrval____) tail:0xc4 end:0xc0 dev:<NULL>
[ 50.474339][ T3480] ------------[ cut here ]------------
[ 50.481132][ T3480] kernel BUG at net/core/skbuff.c:108!
[ 50.486059][ T3480] invalid opcode: 0000 [#1] PREEMPT SMP
[ 50.489463][ T3480] CPU: 3 PID: 3480 Comm: mausezahn Not tainted 5.4.0-rc7 #108
[ 50.492844][ T3480] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.12.0-2.fc30 04/01/2014
[ 50.496551][ T3480] RIP: 0010:skb_panic+0x79/0x7b
[ 50.498261][ T3480] Code: bc 00 00 00 41 57 4c 89 e6 48 c7 c7 90 29 9a 83 4c 8b 8b c0 00 00 00 50 8b 83 b8 00 00 00 50 ff b3 c8 00 00 00 e8 ae ef c0 fe <0f> 0b e8 2f df c8 fe 48 8b 55 08 44 89 f6 4c 89 e7 48 c7 c1 a0 22
[ 50.504111][ T3480] RSP: 0018:ffffc90000447a10 EFLAGS: 00010282
[ 50.505835][ T3480] RAX: 0000000000000087 RBX: ffff888039317d00 RCX: 0000000000000000
[ 50.507900][ T3480] RDX: 0000000000000000 RSI: ffffffff812716e1 RDI: 00000000ffffffff
[ 50.509820][ T3480] RBP: ffffc90000447a60 R08: 0000000000000001 R09: 0000000000000000
[ 50.511735][ T3480] R10: ffffffff81d4f940 R11: 0000000000000000 R12: ffffffff834a22b0
[ 50.513494][ T3480] R13: ffffffff82c10433 R14: 0000000000000088 R15: ffffffff838a8084
[ 50.515222][ T3480] FS: 00007f3536462700(0000) GS:ffff88803eac0000(0000) knlGS:0000000000000000
[ 50.517135][ T3480] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[ 50.518583][ T3480] CR2: 0000000000442008 CR3: 000000003b222000 CR4: 00000000000006e0
[ 50.520723][ T3480] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
[ 50.522709][ T3480] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
[ 50.524450][ T3480] Call Trace:
[ 50.525214][ T3480] skb_put.cold+0x1b/0x1b
[ 50.526171][ T3480] psample_sample_packet+0x1d3/0x340
[ 50.527307][ T3480] tcf_sample_act+0x178/0x250
[ 50.528339][ T3480] tcf_action_exec+0xb1/0x190
[ 50.529354][ T3480] mall_classify+0x67/0x90
[ 50.530332][ T3480] tcf_classify+0x72/0x160
[ 50.531286][ T3480] __dev_queue_xmit+0x3db/0xd50
[ 50.532327][ T3480] dev_queue_xmit+0x18/0x20
[ 50.533299][ T3480] packet_sendmsg+0xee7/0x2090
[ 50.534331][ T3480] sock_sendmsg+0x54/0x70
[ 50.535271][ T3480] __sys_sendto+0x148/0x1f0
[ 50.536252][ T3480] ? tomoyo_file_ioctl+0x23/0x30
[ 50.537334][ T3480] ? ksys_ioctl+0x5e/0xb0
[ 50.540068][ T3480] __x64_sys_sendto+0x2a/0x30
[ 50.542810][ T3480] do_syscall_64+0x73/0x1f0
[ 50.545383][ T3480] entry_SYSCALL_64_after_hwframe+0x44/0xa9
[ 50.548477][ T3480] RIP: 0033:0x7f35357d6fb3
[ 50.551020][ T3480] Code: 48 8b 0d 18 90 20 00 f7 d8 64 89 01 48 83 c8 ff c3 66 0f 1f 44 00 00 83 3d f9 d3 20 00 00 75 13 49 89 ca b8 2c 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 34 c3 48 83 ec 08 e8 eb f6 ff ff 48 89 04 24
[ 50.558547][ T3480] RSP: 002b:00007ffe0c7212c8 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
[ 50.561870][ T3480] RAX: ffffffffffffffda RBX: 0000000001dac010 RCX: 00007f35357d6fb3
[ 50.565142][ T3480] RDX: 0000000000000082 RSI: 0000000001dac2a2 RDI: 0000000000000003
[ 50.568469][ T3480] RBP: 00007ffe0c7212f0 R08: 00007ffe0c7212d0 R09: 0000000000000014
[ 50.571731][ T3480] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000082
[ 50.574961][ T3480] R13: 0000000001dac2a2 R14: 0000000000000001 R15: 0000000000000003
[ 50.578170][ T3480] Modules linked in: sch_ingress virtio_net
[ 50.580976][ T3480] ---[ end trace 61a515626a595af6 ]---

CC: Yotam Gigi <yotamg@xxxxxxxxxxxx>
CC: Jiri Pirko <jiri@xxxxxxxxxxxx>
CC: Jamal Hadi Salim <jhs@xxxxxxxxxxxx>
CC: Simon Horman <simon.horman@xxxxxxxxxxxxx>
CC: Roopa Prabhu <roopa@xxxxxxxxxxxxxxxxxxx>
Fixes: 6ae0a6286171 ("net: Introduce psample, a new genetlink channel for packet sampling")
Signed-off-by: Nikolay Aleksandrov <nikolay@xxxxxxxxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
net/psample/psample.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/net/psample/psample.c
+++ b/net/psample/psample.c
@@ -221,7 +221,7 @@ void psample_sample_packet(struct psampl
data_len = PSAMPLE_MAX_PACKET_SIZE - meta_len - NLA_HDRLEN
- NLA_ALIGNTO;

- nl_skb = genlmsg_new(meta_len + data_len, GFP_ATOMIC);
+ nl_skb = genlmsg_new(meta_len + nla_total_size(data_len), GFP_ATOMIC);
if (unlikely(!nl_skb))
return;