diff options
| author | Jesper Dangaard Brouer <brouer@redhat.com> | 2021-02-09 16:38:09 +0300 |
|---|---|---|
| committer | Daniel Borkmann <daniel@iogearbox.net> | 2021-02-13 03:14:08 +0300 |
| commit | 6306c1189e77a513bf02720450bb43bd4ba5d8ae (patch) | |
| tree | c7fdb60d6d7ec0a2d2ba83c4ec3c698bb9dd7895 /net | |
| parent | 7d4553b69fb335496c597c31590e982485ebe071 (diff) | |
| download | linux-6306c1189e77a513bf02720450bb43bd4ba5d8ae.tar.xz | |
bpf: Remove MTU check in __bpf_skb_max_len
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 <brouer@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/161287788936.790810.2937823995775097177.stgit@firesoul
Diffstat (limited to 'net')
| -rw-r--r-- | net/core/filter.c | 12 |
1 files changed, 4 insertions, 8 deletions
diff --git a/net/core/filter.c b/net/core/filter.c index 57aaed478362..27022168fd78 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -3552,11 +3552,7 @@ static int bpf_skb_net_shrink(struct sk_buff *skb, u32 off, u32 len_diff, return 0; } -static u32 __bpf_skb_max_len(const struct sk_buff *skb) -{ - return skb->dev ? skb->dev->mtu + skb->dev->hard_header_len : - SKB_MAX_ALLOC; -} +#define BPF_SKB_MAX_LEN SKB_MAX_ALLOC BPF_CALL_4(sk_skb_adjust_room, struct sk_buff *, skb, s32, len_diff, u32, mode, u64, flags) @@ -3605,7 +3601,7 @@ BPF_CALL_4(bpf_skb_adjust_room, struct sk_buff *, skb, s32, len_diff, { 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; u32 off; @@ -3688,7 +3684,7 @@ static int bpf_skb_trim_rcsum(struct sk_buff *skb, unsigned int new_len) static inline int __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; @@ -3764,7 +3760,7 @@ static const struct bpf_func_proto sk_skb_change_tail_proto = { static inline int __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; |