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bpf: cleanup bpf_prog_run_{save,clear}_cb helpers 

Move the details behind the cb[] access into a small helper to decouple
and make them generic for bpf_prog_run_save_cb()/bpf_prog_run_clear_cb()
that was introduced via commit ff936a04e5 ("bpf: fix cb access in socket
filter programs"). Also add a comment to better clarify what is done in
bpf_skb_cb().

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Daniel Borkmann 2016-01-06 22:32:16 +01:00 committed by David S. Miller
parent b351a0633e
commit 01dd194c38
1 changed files with 29 additions and 10 deletions
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39
include/linux/filter.h
View File

@ -350,25 +350,43 @@ struct sk_filter {
#define BPF_PROG_RUN(filter, ctx) (*filter->bpf_func)(ctx, filter->insnsi)
#define BPF_SKB_CB_LEN QDISC_CB_PRIV_LEN
static inline u8 *bpf_skb_cb(struct sk_buff *skb)
{
/* eBPF programs may read/write skb->cb[] area to transfer meta
* data between tail calls. Since this also needs to work with
* tc, that scratch memory is mapped to qdisc_skb_cb's data area.
*
* In some socket filter cases, the cb unfortunately needs to be
* saved/restored so that protocol specific skb->cb[] data won't
* be lost. In any case, due to unpriviledged eBPF programs
* attached to sockets, we need to clear the bpf_skb_cb() area
* to not leak previous contents to user space.
*/
BUILD_BUG_ON(FIELD_SIZEOF(struct __sk_buff, cb) != BPF_SKB_CB_LEN);
BUILD_BUG_ON(FIELD_SIZEOF(struct __sk_buff, cb) !=
FIELD_SIZEOF(struct qdisc_skb_cb, data));
return qdisc_skb_cb(skb)->data;
}
static inline u32 bpf_prog_run_save_cb(const struct bpf_prog *prog,
struct sk_buff *skb)
{
u8 *cb_data = qdisc_skb_cb(skb)->data;
u8 saved_cb[QDISC_CB_PRIV_LEN];
u8 *cb_data = bpf_skb_cb(skb);
u8 cb_saved[BPF_SKB_CB_LEN];
u32 res;
BUILD_BUG_ON(FIELD_SIZEOF(struct __sk_buff, cb) !=
QDISC_CB_PRIV_LEN);
if (unlikely(prog->cb_access)) {
memcpy(saved_cb, cb_data, sizeof(saved_cb));
memset(cb_data, 0, sizeof(saved_cb));
memcpy(cb_saved, cb_data, sizeof(cb_saved));
memset(cb_data, 0, sizeof(cb_saved));
}
res = BPF_PROG_RUN(prog, skb);
if (unlikely(prog->cb_access))
memcpy(cb_data, saved_cb, sizeof(saved_cb));
memcpy(cb_data, cb_saved, sizeof(cb_saved));
return res;
}
@ -376,10 +394,11 @@ static inline u32 bpf_prog_run_save_cb(const struct bpf_prog *prog,
static inline u32 bpf_prog_run_clear_cb(const struct bpf_prog *prog,
struct sk_buff *skb)
{
u8 *cb_data = qdisc_skb_cb(skb)->data;
u8 *cb_data = bpf_skb_cb(skb);
if (unlikely(prog->cb_access))
memset(cb_data, 0, QDISC_CB_PRIV_LEN);
memset(cb_data, 0, BPF_SKB_CB_LEN);
return BPF_PROG_RUN(prog, skb);
}