79 lines
2.5 KiB
Diff
79 lines
2.5 KiB
Diff
From: Mathias Krause <minipli@googlemail.com>
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Date: Sun, 13 Apr 2014 18:23:33 +0200
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Subject: filter: prevent nla extensions to peek beyond the end of the message
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Origin: https://git.kernel.org/linus/05ab8f2647e4221cbdb3856dd7d32bd5407316b3
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The BPF_S_ANC_NLATTR and BPF_S_ANC_NLATTR_NEST extensions fail to check
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for a minimal message length before testing the supplied offset to be
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within the bounds of the message. This allows the subtraction of the nla
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header to underflow and therefore -- as the data type is unsigned --
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allowing far to big offset and length values for the search of the
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netlink attribute.
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The remainder calculation for the BPF_S_ANC_NLATTR_NEST extension is
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also wrong. It has the minuend and subtrahend mixed up, therefore
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calculates a huge length value, allowing to overrun the end of the
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message while looking for the netlink attribute.
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The following three BPF snippets will trigger the bugs when attached to
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a UNIX datagram socket and parsing a message with length 1, 2 or 3.
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,-[ PoC for missing size check in BPF_S_ANC_NLATTR ]--
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| ld #0x87654321
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| ldx #42
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| ld #nla
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| ret a
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`---
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,-[ PoC for the same bug in BPF_S_ANC_NLATTR_NEST ]--
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| ld #0x87654321
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| ldx #42
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| ld #nlan
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| ret a
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`---
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,-[ PoC for wrong remainder calculation in BPF_S_ANC_NLATTR_NEST ]--
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| ; (needs a fake netlink header at offset 0)
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| ld #0
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| ldx #42
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| ld #nlan
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| ret a
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`---
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Fix the first issue by ensuring the message length fulfills the minimal
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size constrains of a nla header. Fix the second bug by getting the math
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for the remainder calculation right.
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Fixes: 4738c1db15 ("[SKFILTER]: Add SKF_ADF_NLATTR instruction")
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Fixes: d214c7537b ("filter: add SKF_AD_NLATTR_NEST to look for nested..")
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Cc: Patrick McHardy <kaber@trash.net>
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Cc: Pablo Neira Ayuso <pablo@netfilter.org>
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Signed-off-by: Mathias Krause <minipli@googlemail.com>
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Acked-by: Daniel Borkmann <dborkman@redhat.com>
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Signed-off-by: David S. Miller <davem@davemloft.net>
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[bwh: Backported to 3.14: This code is all in sk_run_filter(), not
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separate functions]
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---
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net/core/filter.c | 8 +++++++-
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1 file changed, 7 insertions(+), 1 deletion(-)
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--- a/net/core/filter.c
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+++ b/net/core/filter.c
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@@ -371,11 +371,15 @@ load_b:
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if (skb_is_nonlinear(skb))
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return 0;
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+ if (skb->len < sizeof(struct nlattr))
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+ return 0;
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+ if (skb->len < sizeof(struct nlattr))
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+ return 0;
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if (A > skb->len - sizeof(struct nlattr))
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return 0;
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nla = (struct nlattr *)&skb->data[A];
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- if (nla->nla_len > A - skb->len)
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+ if (nla->nla_len > skb->len - A)
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return 0;
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nla = nla_find_nested(nla, X);
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