This is a note to let you know that I've just added the patch titled bpf: sockmap, strparser, and tls are reusing qdisc_skb_cb and colliding to the 5.10-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: bpf-sockmap-strparser-and-tls-are-reusing-qdisc_skb_.patch and it can be found in the queue-5.10 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 338bbd8f2fce5081b96a16531ccb07e62475b087 Author: John Fastabend <john.fastabend@xxxxxxxxx> Date: Wed Nov 3 13:47:35 2021 -0700 bpf: sockmap, strparser, and tls are reusing qdisc_skb_cb and colliding [ Upstream commit e0dc3b93bd7bcff8c3813d1df43e0908499c7cf0 ] Strparser is reusing the qdisc_skb_cb struct to stash the skb message handling progress, e.g. offset and length of the skb. First this is poorly named and inherits a struct from qdisc that doesn't reflect the actual usage of cb[] at this layer. But, more importantly strparser is using the following to access its metadata. (struct _strp_msg *)((void *)skb->cb + offsetof(struct qdisc_skb_cb, data)) Where _strp_msg is defined as: struct _strp_msg { struct strp_msg strp; /* 0 8 */ int accum_len; /* 8 4 */ /* size: 12, cachelines: 1, members: 2 */ /* last cacheline: 12 bytes */ }; So we use 12 bytes of ->data[] in struct. However in BPF code running parser and verdict the user has read capabilities into the data[] array as well. Its not too problematic, but we should not be exposing internal state to BPF program. If its really needed then we can use the probe_read() APIs which allow reading kernel memory. And I don't believe cb[] layer poses any API breakage by moving this around because programs can't depend on cb[] across layers. In order to fix another issue with a ctx rewrite we need to stash a temp variable somewhere. To make this work cleanly this patch builds a cb struct for sk_skb types called sk_skb_cb struct. Then we can use this consistently in the strparser, sockmap space. Additionally we can start allowing ->cb[] write access after this. Fixes: 604326b41a6fb ("bpf, sockmap: convert to generic sk_msg interface") Signed-off-by: John Fastabend <john.fastabend@xxxxxxxxx> Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx> Tested-by: Jussi Maki <joamaki@xxxxxxxxx> Reviewed-by: Jakub Sitnicki <jakub@xxxxxxxxxxxxxx> Link: https://lore.kernel.org/bpf/20211103204736.248403-5-john.fastabend@xxxxxxxxx Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/include/net/strparser.h b/include/net/strparser.h index 1d20b98493a10..bec1439bd3be6 100644 --- a/include/net/strparser.h +++ b/include/net/strparser.h @@ -54,10 +54,24 @@ struct strp_msg { int offset; }; +struct _strp_msg { + /* Internal cb structure. struct strp_msg must be first for passing + * to upper layer. + */ + struct strp_msg strp; + int accum_len; +}; + +struct sk_skb_cb { +#define SK_SKB_CB_PRIV_LEN 20 + unsigned char data[SK_SKB_CB_PRIV_LEN]; + struct _strp_msg strp; +}; + static inline struct strp_msg *strp_msg(struct sk_buff *skb) { return (struct strp_msg *)((void *)skb->cb + - offsetof(struct qdisc_skb_cb, data)); + offsetof(struct sk_skb_cb, strp)); } /* Structure for an attached lower socket */ diff --git a/net/core/filter.c b/net/core/filter.c index 7ea752af7894d..abd58dce49bbc 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -9493,6 +9493,27 @@ static u32 sk_skb_convert_ctx_access(enum bpf_access_type type, *insn++ = BPF_LDX_MEM(BPF_SIZEOF(void *), si->dst_reg, si->src_reg, off); break; + case offsetof(struct __sk_buff, cb[0]) ... + offsetofend(struct __sk_buff, cb[4]) - 1: + BUILD_BUG_ON(sizeof_field(struct sk_skb_cb, data) < 20); + BUILD_BUG_ON((offsetof(struct sk_buff, cb) + + offsetof(struct sk_skb_cb, data)) % + sizeof(__u64)); + + prog->cb_access = 1; + off = si->off; + off -= offsetof(struct __sk_buff, cb[0]); + off += offsetof(struct sk_buff, cb); + off += offsetof(struct sk_skb_cb, data); + if (type == BPF_WRITE) + *insn++ = BPF_STX_MEM(BPF_SIZE(si->code), si->dst_reg, + si->src_reg, off); + else + *insn++ = BPF_LDX_MEM(BPF_SIZE(si->code), si->dst_reg, + si->src_reg, off); + break; + + default: return bpf_convert_ctx_access(type, si, insn_buf, prog, target_size); diff --git a/net/strparser/strparser.c b/net/strparser/strparser.c index b3815c1e8f2ea..cd9954c4ad808 100644 --- a/net/strparser/strparser.c +++ b/net/strparser/strparser.c @@ -27,18 +27,10 @@ static struct workqueue_struct *strp_wq; -struct _strp_msg { - /* Internal cb structure. struct strp_msg must be first for passing - * to upper layer. - */ - struct strp_msg strp; - int accum_len; -}; - static inline struct _strp_msg *_strp_msg(struct sk_buff *skb) { return (struct _strp_msg *)((void *)skb->cb + - offsetof(struct qdisc_skb_cb, data)); + offsetof(struct sk_skb_cb, strp)); } /* Lower lock held */