Sashiko pointed out [1]: The hdr pointer passed to bpf_lwt_push_ip_encap() can point to concurrently mutable memory such as a BPF map value.
So, the memory of hdr pointer can be updated after skb_postpush_rcsum(). To fix it, memcpy() the hdr to a local buffer, which will be used for the following checks and updates. [1] https://lore.kernel.org/bpf/[email protected]/ Fixes: 52f278774e79 ("bpf: implement BPF_LWT_ENCAP_IP mode in bpf_lwt_push_encap") Signed-off-by: Leon Hwang <[email protected]> --- net/core/lwt_bpf.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/net/core/lwt_bpf.c b/net/core/lwt_bpf.c index f71ef82a5f3d..8009e427851f 100644 --- a/net/core/lwt_bpf.c +++ b/net/core/lwt_bpf.c @@ -599,6 +599,7 @@ static int handle_gso_encap(struct sk_buff *skb, bool ipv4, int encap_len) int bpf_lwt_push_ip_encap(struct sk_buff *skb, void *hdr, u32 len, bool ingress) { + u8 buff[LWT_BPF_MAX_HEADROOM]; struct iphdr *iph; bool ipv4; int err; @@ -606,8 +607,10 @@ int bpf_lwt_push_ip_encap(struct sk_buff *skb, void *hdr, u32 len, bool ingress) if (unlikely(len < sizeof(struct iphdr) || len > LWT_BPF_MAX_HEADROOM)) return -EINVAL; + memcpy(buff, hdr, len); + /* validate protocol and length */ - iph = (struct iphdr *)hdr; + iph = (struct iphdr *)buff; if (iph->version == 4) { ipv4 = true; if (unlikely(len < iph->ihl * 4)) @@ -637,7 +640,7 @@ int bpf_lwt_push_ip_encap(struct sk_buff *skb, void *hdr, u32 len, bool ingress) if (ingress) skb_postpush_rcsum(skb, iph, len); skb_reset_network_header(skb); - memcpy(skb_network_header(skb), hdr, len); + memcpy(skb_network_header(skb), buff, len); bpf_compute_data_pointers(skb); skb_clear_hash(skb); -- 2.54.0
