On 7/12/22 6:58 PM, sdf@xxxxxxxxxx wrote:
On 07/12, Zhengchao Shao wrote:
Syzbot found an issue [1]: fq_codel_drop() try to drop a flow whitout any
skbs, that is, the flow->head is null.
The root cause, as the [2] says, is because that bpf_prog_test_run_skb()
run a bpf prog which redirects empty skbs.
So we should determine whether the length of the packet modified by bpf
prog or others like bpf_prog_test is valid before forwarding it directly.
LINK: [1] https://syzkaller.appspot.com/bug?id=0b84da80c2917757915afa89f7738a9d16ec96c5
LINK: [2] https://www.spinics.net/lists/netdev/msg777503.html
Reported-by: syzbot+7a12909485b94426aceb@xxxxxxxxxxxxxxxxxxxxxxxxx
Signed-off-by: Zhengchao Shao <shaozhengchao@xxxxxxxxxx>
---
net/core/filter.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/net/core/filter.c b/net/core/filter.c
index 4ef77ec5255e..27801b314960 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -2122,6 +2122,11 @@ static int __bpf_redirect_no_mac(struct sk_buff *skb, struct net_device *dev,
{
unsigned int mlen = skb_network_offset(skb);
+ if (unlikely(skb->len == 0)) {
+ kfree_skb(skb);
+ return -EINVAL;
+ }
+
if (mlen) {
__skb_pull(skb, mlen);
@@ -2143,7 +2148,9 @@ static int __bpf_redirect_common(struct sk_buff *skb, struct net_device *dev,
u32 flags)
{
/* Verify that a link layer header is carried */
- if (unlikely(skb->mac_header >= skb->network_header)) {
+ if (unlikely(skb->mac_header >= skb->network_header) ||
+ (min_t(u32, skb_mac_header_len(skb), skb->len) <
+ (u32)dev->min_header_len)) {
Why check skb->len != 0 above but skb->len < dev->min_header_len here?
I guess it doesn't make sense in __bpf_redirect_no_mac because we know
that mac is empty, but why do we care in __bpf_redirect_common?
Why not put this check in the common __bpf_redirect?
Also, it's still not clear to me whether we should bake it into the core
stack vs having some special checks from test_prog_run only. I'm
assuming the issue is that we can construct illegal skbs with that
test_prog_run interface, so maybe start by fixing that?
Agree, ideally we can prevent it right at the source rather than adding
more tests into the fast-path.
Did you have a chance to look at the reproducer more closely? What
exactly is it doing?
kfree_skb(skb);
return -ERANGE;
}
--
2.17.1
