Messages in this thread Patch in this message | | | From | Ben Hutchings <> | Date | Sat, 07 Jun 2014 02:26:28 +0100 | Subject | [PATCH 3.2 12/92] filter: prevent nla extensions to peek beyond the end of the message |
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3.2.60-rc1 review patch. If anyone has any objections, please let me know.
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From: Mathias Krause <minipli@googlemail.com>
[ Upstream commit 05ab8f2647e4221cbdb3856dd7d32bd5407316b3 ]
The BPF_S_ANC_NLATTR and BPF_S_ANC_NLATTR_NEST extensions fail to check for a minimal message length before testing the supplied offset to be within the bounds of the message. This allows the subtraction of the nla header to underflow and therefore -- as the data type is unsigned -- allowing far to big offset and length values for the search of the netlink attribute.
The remainder calculation for the BPF_S_ANC_NLATTR_NEST extension is also wrong. It has the minuend and subtrahend mixed up, therefore calculates a huge length value, allowing to overrun the end of the message while looking for the netlink attribute.
The following three BPF snippets will trigger the bugs when attached to a UNIX datagram socket and parsing a message with length 1, 2 or 3.
,-[ PoC for missing size check in BPF_S_ANC_NLATTR ]-- | ld #0x87654321 | ldx #42 | ld #nla | ret a `---
,-[ PoC for the same bug in BPF_S_ANC_NLATTR_NEST ]-- | ld #0x87654321 | ldx #42 | ld #nlan | ret a `---
,-[ PoC for wrong remainder calculation in BPF_S_ANC_NLATTR_NEST ]-- | ; (needs a fake netlink header at offset 0) | ld #0 | ldx #42 | ld #nlan | ret a `---
Fix the first issue by ensuring the message length fulfills the minimal size constrains of a nla header. Fix the second bug by getting the math for the remainder calculation right.
Fixes: 4738c1db15 ("[SKFILTER]: Add SKF_ADF_NLATTR instruction") Fixes: d214c7537b ("filter: add SKF_AD_NLATTR_NEST to look for nested..") Cc: Patrick McHardy <kaber@trash.net> Cc: Pablo Neira Ayuso <pablo@netfilter.org> Signed-off-by: Mathias Krause <minipli@googlemail.com> Acked-by: Daniel Borkmann <dborkman@redhat.com> Signed-off-by: David S. Miller <davem@davemloft.net> [bwh: Fix misplacement of the first check due to a bug in the patch program] Signed-off-by: Ben Hutchings <ben@decadent.org.uk> --- net/core/filter.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-)
--- a/net/core/filter.c +++ b/net/core/filter.c @@ -320,6 +320,8 @@ load_b: if (skb_is_nonlinear(skb)) return 0; + if (skb->len < sizeof(struct nlattr)) + return 0; if (A > skb->len - sizeof(struct nlattr)) return 0; @@ -336,11 +338,13 @@ load_b: if (skb_is_nonlinear(skb)) return 0; + if (skb->len < sizeof(struct nlattr)) + return 0; if (A > skb->len - sizeof(struct nlattr)) return 0; nla = (struct nlattr *)&skb->data[A]; - if (nla->nla_len > A - skb->len) + if (nla->nla_len > skb->len - A) return 0; nla = nla_find_nested(nla, X);
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