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net/tap: fix eBPF handling of non-RSS flows

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The eBPF classifier (section "cls_q" in tap_bpf_program.c) is tracing
marked packets in which skb->cb[1] contains an RSS queue number, and
redirects those packets to the matched queue.
It is expected that skb->cb[1] has been previously set with a valid RSS
queue number during an eBPF action (section "l3_l4" in tap_bpf_program.c).
However, for non-RSS flows, skb->cb[1] may contain a random unset value,
which could falsely be interpreted as a valid RSS queue.
To avoid this potential error, tap_bpf_program.c has been updated as
follows:
1. After calculating the RSS queue number, it is added a unique offset in
order to uniquely identify it as a valid RSS queue number.
2. After matching an RSS queue to a packet, skb->cb[1] is set to 0.

Fixes: cdc07e83bb24 ("net/tap: add eBPF program file")
Fixes: aabe70df73a3 ("net/tap: add eBPF bytes code")

Signed-off-by: Ophir Munk <ophirmu@mellanox.com>
Acked-by: Pascal Mazon <pascal.mazon@6wind.com>
This commit is contained in:
Ophir Munk 2018-02-05 14:40:42 +00:00 committed by Ferruh Yigit
parent 9abaad8d68
commit 54aad2f231
2 changed files with 19 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

23
drivers/net/tap/tap_bpf_insns.h
View File

@ -6,17 +6,20 @@
/* bpf_insn array matching cls_q section. See tap_bpf_program.c file */
struct bpf_insn cls_q_insns[] = {
{0x61, 1, 1, 52, 0x00000000},
{0x18, 2, 0, 0, 0xdeadbeef},
{0x61, 2, 1, 52, 0x00000000},
{0x18, 3, 0, 0, 0xdeadbeef},
{0x00, 0, 0, 0, 0x00000000},
{0x63, 10, 2, -4, 0x00000000},
{0x61, 2, 10, -4, 0x00000000},
{0x07, 2, 0, 0, 0x00000001},
{0x67, 2, 0, 0, 0x00000020},
{0x77, 2, 0, 0, 0x00000020},
{0xb7, 0, 0, 0, 0xffffffff},
{0x1d, 1, 2, 1, 0x00000000},
{0x63, 10, 3, -4, 0x00000000},
{0xb7, 0, 0, 0, 0x00000000},
{0x61, 3, 10, -4, 0x00000000},
{0x07, 3, 0, 0, 0x7cafe800},
{0x67, 3, 0, 0, 0x00000020},
{0x77, 3, 0, 0, 0x00000020},
{0x5d, 2, 3, 4, 0x00000000},
{0xb7, 2, 0, 0, 0x00000000},
{0x63, 1, 2, 52, 0x00000000},
{0x18, 0, 0, 0, 0xffffffff},
{0x00, 0, 0, 0, 0x00000000},
{0x95, 0, 0, 0, 0x00000000},
};
@ -1685,7 +1688,7 @@ struct bpf_insn l3_l4_hash_insns[] = {
{0x4f, 3, 2, 0, 0x00000000},
{0x67, 3, 0, 0, 0x00000010},
{0x4f, 3, 1, 0, 0x00000000},
{0x07, 3, 0, 0, 0x00000001},
{0x07, 3, 0, 0, 0x7cafe800},
{0x63, 5, 3, 52, 0x00000000},
{0xb7, 7, 0, 0, 0x00000001},
{0xbf, 0, 7, 0, 0x00000000},

9
drivers/net/tap/tap_bpf_program.c
View File

@ -28,10 +28,10 @@
((b) & 0xff))
/*
* The queue number is offset by 1, to distinguish packets that have
* gone through this rule (skb->cb[1] != 0) from others.
* The queue number is offset by a unique QUEUE_OFFSET, to distinguish
* packets that have gone through this rule (skb->cb[1] != 0) from others.
*/
#define QUEUE_OFFSET 1
#define QUEUE_OFFSET 0x7cafe800
#define PIN_GLOBAL_NS 2
#define KEY_IDX 0
@ -63,6 +63,9 @@ match_q(struct __sk_buff *skb)
if (queue != match_queue)
return TC_ACT_OK;
/* queue match */
skb->cb[1] = 0;
return TC_ACT_UNSPEC;
}