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author | Shmulik Ladkani <shmulik@metanetworks.com> | 2019-09-06 12:23:50 +0300 |
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committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2019-09-21 08:14:02 +0300 |
commit | 162a5a8c3aff15c449e6b38355cdf80ab4f77a5a (patch) | |
tree | 4514add64ed273714dc4be100ba8cbffe4de8709 /net | |
parent | 905bf350353153b0c3ef60bdc4604c0c8a83d6c3 (diff) | |
download | linux-162a5a8c3aff15c449e6b38355cdf80ab4f77a5a.tar.xz |
net: gso: Fix skb_segment splat when splitting gso_size mangled skb having linear-headed frag_list
[ Upstream commit 3dcbdb134f329842a38f0e6797191b885ab00a00 ]
Historically, support for frag_list packets entering skb_segment() was
limited to frag_list members terminating on exact same gso_size
boundaries. This is verified with a BUG_ON since commit 89319d3801d1
("net: Add frag_list support to skb_segment"), quote:
As such we require all frag_list members terminate on exact MSS
boundaries. This is checked using BUG_ON.
As there should only be one producer in the kernel of such packets,
namely GRO, this requirement should not be difficult to maintain.
However, since commit 6578171a7ff0 ("bpf: add bpf_skb_change_proto helper"),
the "exact MSS boundaries" assumption no longer holds:
An eBPF program using bpf_skb_change_proto() DOES modify 'gso_size', but
leaves the frag_list members as originally merged by GRO with the
original 'gso_size'. Example of such programs are bpf-based NAT46 or
NAT64.
This lead to a kernel BUG_ON for flows involving:
- GRO generating a frag_list skb
- bpf program performing bpf_skb_change_proto() or bpf_skb_adjust_room()
- skb_segment() of the skb
See example BUG_ON reports in [0].
In commit 13acc94eff12 ("net: permit skb_segment on head_frag frag_list skb"),
skb_segment() was modified to support the "gso_size mangling" case of
a frag_list GRO'ed skb, but *only* for frag_list members having
head_frag==true (having a page-fragment head).
Alas, GRO packets having frag_list members with a linear kmalloced head
(head_frag==false) still hit the BUG_ON.
This commit adds support to skb_segment() for a 'head_skb' packet having
a frag_list whose members are *non* head_frag, with gso_size mangled, by
disabling SG and thus falling-back to copying the data from the given
'head_skb' into the generated segmented skbs - as suggested by Willem de
Bruijn [1].
Since this approach involves the penalty of skb_copy_and_csum_bits()
when building the segments, care was taken in order to enable this
solution only when required:
- untrusted gso_size, by testing SKB_GSO_DODGY is set
(SKB_GSO_DODGY is set by any gso_size mangling functions in
net/core/filter.c)
- the frag_list is non empty, its item is a non head_frag, *and* the
headlen of the given 'head_skb' does not match the gso_size.
[0]
https://lore.kernel.org/netdev/20190826170724.25ff616f@pixies/
https://lore.kernel.org/netdev/9265b93f-253d-6b8c-f2b8-4b54eff1835c@fb.com/
[1]
https://lore.kernel.org/netdev/CA+FuTSfVsgNDi7c=GUU8nMg2hWxF2SjCNLXetHeVPdnxAW5K-w@mail.gmail.com/
Fixes: 6578171a7ff0 ("bpf: add bpf_skb_change_proto helper")
Suggested-by: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Alexander Duyck <alexander.duyck@gmail.com>
Signed-off-by: Shmulik Ladkani <shmulik.ladkani@gmail.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Reviewed-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'net')
-rw-r--r-- | net/core/skbuff.c | 19 |
1 files changed, 19 insertions, 0 deletions
diff --git a/net/core/skbuff.c b/net/core/skbuff.c index 4a71d78d0c6a..7164569c1ec8 100644 --- a/net/core/skbuff.c +++ b/net/core/skbuff.c @@ -3094,6 +3094,25 @@ struct sk_buff *skb_segment(struct sk_buff *head_skb, int pos; int dummy; + if (list_skb && !list_skb->head_frag && skb_headlen(list_skb) && + (skb_shinfo(head_skb)->gso_type & SKB_GSO_DODGY)) { + /* gso_size is untrusted, and we have a frag_list with a linear + * non head_frag head. + * + * (we assume checking the first list_skb member suffices; + * i.e if either of the list_skb members have non head_frag + * head, then the first one has too). + * + * If head_skb's headlen does not fit requested gso_size, it + * means that the frag_list members do NOT terminate on exact + * gso_size boundaries. Hence we cannot perform skb_frag_t page + * sharing. Therefore we must fallback to copying the frag_list + * skbs; we do so by disabling SG. + */ + if (mss != GSO_BY_FRAGS && mss != skb_headlen(head_skb)) + features &= ~NETIF_F_SG; + } + __skb_push(head_skb, doffset); proto = skb_network_protocol(head_skb, &dummy); if (unlikely(!proto)) |