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authorJohn Fastabend <john.fastabend@gmail.com>2017-10-27 09:45:34 -0700
committerDavid S. Miller <davem@davemloft.net>2017-10-29 11:18:48 +0900
commit8108a77515126f6db4374e8593956e20430307c0 (patch)
tree0c6e1ae0c05ad353f1fa675edcdaad6cf9b333b3
parentdea6e19f4ef746aa18b4c33d1a7fed54356796ed (diff)
downloadlinux-stericsson-8108a77515126f6db4374e8593956e20430307c0.tar.gz
bpf: bpf_compute_data uses incorrect cb structure
SK_SKB program types use bpf_compute_data to store the end of the packet data. However, bpf_compute_data assumes the cb is stored in the qdisc layer format. But, for SK_SKB this is the wrong layer of the stack for this type. It happens to work (sort of!) because in most cases nothing happens to be overwritten today. This is very fragile and error prone. Fortunately, we have another hole in tcp_skb_cb we can use so lets put the data_end value there. Note, SK_SKB program types do not use data_meta, they are failed by sk_skb_is_valid_access(). Signed-off-by: John Fastabend <john.fastabend@gmail.com> Acked-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: David S. Miller <davem@davemloft.net>
-rw-r--r--include/net/tcp.h1
-rw-r--r--kernel/bpf/sockmap.c12
-rw-r--r--net/core/filter.c27
3 files changed, 37 insertions, 3 deletions
diff --git a/include/net/tcp.h b/include/net/tcp.h
index b1ef98ebce53..33599d17522d 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -844,6 +844,7 @@ struct tcp_skb_cb {
__u32 key;
__u32 flags;
struct bpf_map *map;
+ void *data_end;
} bpf;
};
};
diff --git a/kernel/bpf/sockmap.c b/kernel/bpf/sockmap.c
index 2b6eb35ae5d3..6778fb773934 100644
--- a/kernel/bpf/sockmap.c
+++ b/kernel/bpf/sockmap.c
@@ -93,6 +93,14 @@ static inline struct smap_psock *smap_psock_sk(const struct sock *sk)
return rcu_dereference_sk_user_data(sk);
}
+/* compute the linear packet data range [data, data_end) for skb when
+ * sk_skb type programs are in use.
+ */
+static inline void bpf_compute_data_end_sk_skb(struct sk_buff *skb)
+{
+ TCP_SKB_CB(skb)->bpf.data_end = skb->data + skb_headlen(skb);
+}
+
static int smap_verdict_func(struct smap_psock *psock, struct sk_buff *skb)
{
struct bpf_prog *prog = READ_ONCE(psock->bpf_verdict);
@@ -108,7 +116,7 @@ static int smap_verdict_func(struct smap_psock *psock, struct sk_buff *skb)
*/
TCP_SKB_CB(skb)->bpf.map = NULL;
skb->sk = psock->sock;
- bpf_compute_data_end(skb);
+ bpf_compute_data_end_sk_skb(skb);
preempt_disable();
rc = (*prog->bpf_func)(skb, prog->insnsi);
preempt_enable();
@@ -368,7 +376,7 @@ static int smap_parse_func_strparser(struct strparser *strp,
* any socket yet.
*/
skb->sk = psock->sock;
- bpf_compute_data_end(skb);
+ bpf_compute_data_end_sk_skb(skb);
rc = (*prog->bpf_func)(skb, prog->insnsi);
skb->sk = NULL;
rcu_read_unlock();
diff --git a/net/core/filter.c b/net/core/filter.c
index aa0265997f93..68eaa2f81a8e 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -4243,6 +4243,31 @@ static u32 sock_ops_convert_ctx_access(enum bpf_access_type type,
return insn - insn_buf;
}
+static u32 sk_skb_convert_ctx_access(enum bpf_access_type type,
+ const struct bpf_insn *si,
+ struct bpf_insn *insn_buf,
+ struct bpf_prog *prog, u32 *target_size)
+{
+ struct bpf_insn *insn = insn_buf;
+ int off;
+
+ switch (si->off) {
+ case offsetof(struct __sk_buff, data_end):
+ off = si->off;
+ off -= offsetof(struct __sk_buff, data_end);
+ off += offsetof(struct sk_buff, cb);
+ off += offsetof(struct tcp_skb_cb, bpf.data_end);
+ *insn++ = BPF_LDX_MEM(BPF_SIZEOF(void *), si->dst_reg,
+ si->src_reg, off);
+ break;
+ default:
+ return bpf_convert_ctx_access(type, si, insn_buf, prog,
+ target_size);
+ }
+
+ return insn - insn_buf;
+}
+
const struct bpf_verifier_ops sk_filter_prog_ops = {
.get_func_proto = sk_filter_func_proto,
.is_valid_access = sk_filter_is_valid_access,
@@ -4301,7 +4326,7 @@ const struct bpf_verifier_ops sock_ops_prog_ops = {
const struct bpf_verifier_ops sk_skb_prog_ops = {
.get_func_proto = sk_skb_func_proto,
.is_valid_access = sk_skb_is_valid_access,
- .convert_ctx_access = bpf_convert_ctx_access,
+ .convert_ctx_access = sk_skb_convert_ctx_access,
.gen_prologue = sk_skb_prologue,
};