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| author | Jesper Dangaard Brouer <brouer@redhat.com> | 2021-02-09 16:38:09 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2021-04-07 13:05:40 +0300 |
| commit | 1636af9e8a8840f5696ad2c01130832411986af4 (patch) | |
| tree | 2b4df68d31619aea2cfffa30141451b2819ec268 | |
| parent | 963d1af3e064f256e38752cb5a9bfd7a81369066 (diff) | |
| download | linux-1636af9e8a8840f5696ad2c01130832411986af4.tar.xz | |
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 <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
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | net/core/filter.c | 7 |
1 files changed, 2 insertions, 5 deletions
diff --git a/net/core/filter.c b/net/core/filter.c index e8c89d2d2bc0..94bf897485db 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -2120,10 +2120,7 @@ static u32 __bpf_skb_min_len(const struct sk_buff *skb) return min_len; } -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_grow_rcsum(struct sk_buff *skb, unsigned int new_len) { @@ -2144,7 +2141,7 @@ 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; |