From: Mathias Krause Date: Sun, 13 Apr 2014 16:23:33 +0000 (+0200) Subject: filter: prevent nla extensions to peek beyond the end of the message X-Git-Url: http://git.efficios.com/?p=deliverable%2Flinux.git;a=commitdiff_plain;h=05ab8f2647e4221cbdb3856dd7d32bd5407316b3 filter: prevent nla extensions to peek beyond the end of the message 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 Cc: Pablo Neira Ayuso Signed-off-by: Mathias Krause Acked-by: Daniel Borkmann Signed-off-by: David S. Miller --- diff --git a/net/core/filter.c b/net/core/filter.c index e08b3822c72a..0e0856f5d708 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);