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authorJohn Fastabend <john.fastabend@gmail.com>2021-11-03 13:47:35 -0700
committerDaniel Borkmann <daniel@iogearbox.net>2021-11-09 01:05:28 +0100
commite0dc3b93bd7bcff8c3813d1df43e0908499c7cf0 (patch)
treebd7c01abcf6ac456283db72e6fb92d691d357e89 /net/strparser
parentc5d2177a72a1659554922728fc407f59950aa929 (diff)
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 <john.fastabend@gmail.com> Signed-off-by: Daniel Borkmann <daniel@iogearbox.net> Tested-by: Jussi Maki <joamaki@gmail.com> Reviewed-by: Jakub Sitnicki <jakub@cloudflare.com> Link: https://lore.kernel.org/bpf/20211103204736.248403-5-john.fastabend@gmail.com
Diffstat (limited to 'net/strparser')
-rw-r--r--net/strparser/strparser.c10
1 files changed, 1 insertions, 9 deletions
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 */