From e0dc3b93bd7bcff8c3813d1df43e0908499c7cf0 Mon Sep 17 00:00:00 2001 From: John Fastabend Date: Wed, 3 Nov 2021 13:47:35 -0700 Subject: bpf: sockmap, strparser, and tls are reusing qdisc_skb_cb and colliding 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 Signed-off-by: Daniel Borkmann Tested-by: Jussi Maki Reviewed-by: Jakub Sitnicki Link: https://lore.kernel.org/bpf/20211103204736.248403-5-john.fastabend@gmail.com --- net/strparser/strparser.c | 10 +--------- 1 file changed, 1 insertion(+), 9 deletions(-) (limited to 'net/strparser') diff --git a/net/strparser/strparser.c b/net/strparser/strparser.c index 9c0343568d2a..1a72c67afed5 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 */ -- cgit v1.2.3