| Message ID | 1397406213-15452-1-git-send-email-minipli@googlemail.com |
|---|---|
| State | Accepted, archived |
| Delegated to: | David Miller |
| Headers | show |
On 04/13/2014 06:23 PM, Mathias Krause wrote: > 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 und 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> -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
From: Mathias Krause <minipli@googlemail.com> Date: Sun, 13 Apr 2014 18:23:33 +0200 > 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 und subtrahend mixed up, therefore I translated the German into English here, re: und --> and :-) > 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> > --- > Backporters will find the code in question in the switch block of > sk_run_filter(). Thanks, applied and queued up for -stable. -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 14 April 2014 05:33, David Miller <davem@davemloft.net> wrote: > From: Mathias Krause <minipli@googlemail.com> > Date: Sun, 13 Apr 2014 18:23:33 +0200 > >> 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 und subtrahend mixed up, therefore > > I translated the German into English here, re: und --> and :-) > Ups! :D Thanks for the review! Cheers, Mathias -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/net/core/filter.c b/net/core/filter.c index e08b3822c7..0e0856f5d7 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -600,6 +600,9 @@ static u64 __skb_get_nlattr(u64 ctx, u64 A, u64 X, u64 r4, u64 r5) if (skb_is_nonlinear(skb)) return 0; + if (skb->len < sizeof(struct nlattr)) + return 0; + if (A > skb->len - sizeof(struct nlattr)) return 0; @@ -618,11 +621,14 @@ static u64 __skb_get_nlattr_nest(u64 ctx, u64 A, u64 X, u64 r4, u64 r5) 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);
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 und 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> --- Backporters will find the code in question in the switch block of sk_run_filter(). net/core/filter.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)