| From foo@baz Wed May 28 21:03:54 PDT 2014 |
| From: Mathias Krause <minipli@googlemail.com> |
| Date: Sun, 13 Apr 2014 18:23:33 +0200 |
| Subject: filter: prevent nla extensions to peek beyond the end of the message |
| |
| 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> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| --- |
| net/core/filter.c | 6 +++++- |
| 1 file changed, 5 insertions(+), 1 deletion(-) |
| |
| --- a/net/core/filter.c |
| +++ b/net/core/filter.c |
| @@ -355,6 +355,8 @@ 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; |
| |
| @@ -371,11 +373,13 @@ 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); |