| Message ID | 20200820190550.7736-1-fw@strlen.de |
|---|---|
| State | Accepted |
| Delegated to: | Pablo Neira |
| Headers | show |
| Series | [nf,v2] netfilter: nf_tables: fix destination register zeroing | expand |
On Thu, Aug 20, 2020 at 09:05:50PM +0200, Florian Westphal wrote: > Following bug was reported via irc: > nft list ruleset > set knock_candidates_ipv4 { > type ipv4_addr . inet_service > size 65535 > elements = { 127.0.0.1 . 123, > 127.0.0.1 . 123 } > } > .. > udp dport 123 add @knock_candidates_ipv4 { ip saddr . 123 } > udp dport 123 add @knock_candidates_ipv4 { ip saddr . udp dport } > > It should not have been possible to add a duplicate set entry. > > After some debugging it turned out that the problem is the immediate > value (123) in the second-to-last rule. > > Concatenations use 32bit registers, i.e. the elements are 8 bytes each, > not 6 and it turns out the kernel inserted > > inet firewall @knock_candidates_ipv4 > element 0100007f ffff7b00 : 0 [end] > element 0100007f 00007b00 : 0 [end] > > Note the non-zero upper bits of the first element. It turns out that > nft_immediate doesn't zero the destination register, but this is needed > when the length isn't a multiple of 4. > > Furthermore, the zeroing in nft_payload is broken. We can't use > [len / 4] = 0 -- if len is a multiple of 4, index is off by one. > > Skip zeroing in this case and use a conditional instead of (len -1) / 4. Applied, thanks.
diff --git a/include/net/netfilter/nf_tables.h b/include/net/netfilter/nf_tables.h index bf9491b77d16..224d194ad29d 100644 --- a/include/net/netfilter/nf_tables.h +++ b/include/net/netfilter/nf_tables.h @@ -143,6 +143,8 @@ static inline u64 nft_reg_load64(const u32 *sreg) static inline void nft_data_copy(u32 *dst, const struct nft_data *src, unsigned int len) { + if (len % NFT_REG32_SIZE) + dst[len / NFT_REG32_SIZE] = 0; memcpy(dst, src, len); } diff --git a/net/netfilter/nft_payload.c b/net/netfilter/nft_payload.c index ed7cb9f747f6..7a2e59638499 100644 --- a/net/netfilter/nft_payload.c +++ b/net/netfilter/nft_payload.c @@ -87,7 +87,9 @@ void nft_payload_eval(const struct nft_expr *expr, u32 *dest = ®s->data[priv->dreg]; int offset; - dest[priv->len / NFT_REG32_SIZE] = 0; + if (priv->len % NFT_REG32_SIZE) + dest[priv->len / NFT_REG32_SIZE] = 0; + switch (priv->base) { case NFT_PAYLOAD_LL_HEADER: if (!skb_mac_header_was_set(skb))
Following bug was reported via irc: nft list ruleset set knock_candidates_ipv4 { type ipv4_addr . inet_service size 65535 elements = { 127.0.0.1 . 123, 127.0.0.1 . 123 } } .. udp dport 123 add @knock_candidates_ipv4 { ip saddr . 123 } udp dport 123 add @knock_candidates_ipv4 { ip saddr . udp dport } It should not have been possible to add a duplicate set entry. After some debugging it turned out that the problem is the immediate value (123) in the second-to-last rule. Concatenations use 32bit registers, i.e. the elements are 8 bytes each, not 6 and it turns out the kernel inserted inet firewall @knock_candidates_ipv4 element 0100007f ffff7b00 : 0 [end] element 0100007f 00007b00 : 0 [end] Note the non-zero upper bits of the first element. It turns out that nft_immediate doesn't zero the destination register, but this is needed when the length isn't a multiple of 4. Furthermore, the zeroing in nft_payload is broken. We can't use [len / 4] = 0 -- if len is a multiple of 4, index is off by one. Skip zeroing in this case and use a conditional instead of (len -1) / 4. Fixes: 49499c3e6e18 ("netfilter: nf_tables: switch registers to 32 bit addressing") Signed-off-by: Florian Westphal <fw@strlen.de> --- v2: revisit commit message. No other changes. include/net/netfilter/nf_tables.h | 2 ++ net/netfilter/nft_payload.c | 4 +++- 2 files changed, 5 insertions(+), 1 deletion(-)