From: Jesper Dangaard Brouer Date: Tue, 9 Feb 2021 13:38:09 +0000 (+0100) Subject: bpf: Remove MTU check in __bpf_skb_max_len X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=c2ef87b75fe771671d2d2af8fa245eebc0f348b6;p=GitHub%2FLineageOS%2Fandroid_kernel_motorola_exynos9610.git bpf: Remove MTU check in __bpf_skb_max_len commit 6306c1189e77a513bf02720450bb43bd4ba5d8ae upstream. Multiple BPF-helpers that can manipulate/increase the size of the SKB uses __bpf_skb_max_len() as the max-length. This function limit size against the current net_device MTU (skb->dev->mtu). When a BPF-prog grow the packet size, then it should not be limited to the MTU. The MTU is a transmit limitation, and software receiving this packet should be allowed to increase the size. Further more, current MTU check in __bpf_skb_max_len uses the MTU from ingress/current net_device, which in case of redirects uses the wrong net_device. This patch keeps a sanity max limit of SKB_MAX_ALLOC (16KiB). The real limit is elsewhere in the system. Jesper's testing[1] showed it was not possible to exceed 8KiB when expanding the SKB size via BPF-helper. The limiting factor is the define KMALLOC_MAX_CACHE_SIZE which is 8192 for SLUB-allocator (CONFIG_SLUB) in-case PAGE_SIZE is 4096. This define is in-effect due to this being called from softirq context see code __gfp_pfmemalloc_flags() and __do_kmalloc_node(). Jakub's testing showed that frames above 16KiB can cause NICs to reset (but not crash). Keep this sanity limit at this level as memory layer can differ based on kernel config. [1] https://github.com/xdp-project/bpf-examples/tree/master/MTU-tests Signed-off-by: Jesper Dangaard Brouer Signed-off-by: Daniel Borkmann Acked-by: John Fastabend Link: https://lore.kernel.org/bpf/161287788936.790810.2937823995775097177.stgit@firesoul Signed-off-by: Greg Kroah-Hartman --- diff --git a/net/core/filter.c b/net/core/filter.c index 912a4cfb4384..e4c48941d83e 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -2279,17 +2279,14 @@ static int bpf_skb_net_shrink(struct sk_buff *skb, u32 len_diff) return 0; } -static u32 __bpf_skb_max_len(const struct sk_buff *skb) -{ - return skb->dev->mtu + skb->dev->hard_header_len; -} +#define BPF_SKB_MAX_LEN SKB_MAX_ALLOC static int bpf_skb_adjust_net(struct sk_buff *skb, s32 len_diff) { bool trans_same = skb->transport_header == skb->network_header; u32 len_cur, len_diff_abs = abs(len_diff); u32 len_min = bpf_skb_net_base_len(skb); - u32 len_max = __bpf_skb_max_len(skb); + u32 len_max = BPF_SKB_MAX_LEN; __be16 proto = skb->protocol; bool shrink = len_diff < 0; int ret; @@ -2368,7 +2365,7 @@ static int bpf_skb_trim_rcsum(struct sk_buff *skb, unsigned int new_len) BPF_CALL_3(bpf_skb_change_tail, struct sk_buff *, skb, u32, new_len, u64, flags) { - u32 max_len = __bpf_skb_max_len(skb); + u32 max_len = BPF_SKB_MAX_LEN; u32 min_len = __bpf_skb_min_len(skb); int ret; @@ -2419,7 +2416,7 @@ static const struct bpf_func_proto bpf_skb_change_tail_proto = { BPF_CALL_3(bpf_skb_change_head, struct sk_buff *, skb, u32, head_room, u64, flags) { - u32 max_len = __bpf_skb_max_len(skb); + u32 max_len = BPF_SKB_MAX_LEN; u32 new_len = skb->len + head_room; int ret;