[PATCH 5.4 019/154] netfilter: nft_exthdr: fix offset with ipv4_find_option()

Greg Kroah-Hartman
2025-04-08T12:03:03Z

From: Alexey Kashavkin <akashavkin@gmail.com>

[ Upstream commit 6edd78af9506bb182518da7f6feebd75655d9a0e ]

There is an incorrect calculation in the offset variable which causes
the nft_skb_copy_to_reg() function to always return -EFAULT. Adding the
start variable is redundant. In the __ip_options_compile() function the
correct offset is specified when finding the function. There is no need
to add the size of the iphdr structure to the offset.

Fixes: dbb5281a1f84 ("netfilter: nf_tables: add support for matching IPv4 options")
Signed-off-by: Alexey Kashavkin <akashavkin@gmail.com>
Reviewed-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
net/netfilter/nft_exthdr.c | 10 ++++------
1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/net/netfilter/nft_exthdr.c b/net/netfilter/nft_exthdr.c
index ca268293cfa12..de43abf6d1191 100644
--- a/net/netfilter/nft_exthdr.c
+++ b/net/netfilter/nft_exthdr.c
@@ -83,7 +83,6 @@ static int ipv4_find_option(struct net *net, struct sk_buff *skb,
unsigned char optbuf[sizeof(struct ip_options) + 40];
struct ip_options *opt = (struct ip_options *)optbuf;
struct iphdr *iph, _iph;
- unsigned int start;
bool found = false;
__be32 info;
int optlen;
@@ -91,7 +90,6 @@ static int ipv4_find_option(struct net *net, struct sk_buff *skb,
iph = skb_header_pointer(skb, 0, sizeof(_iph), &_iph);
if (!iph)
return -EBADMSG;
- start = sizeof(struct iphdr);

optlen = iph->ihl * 4 - (int)sizeof(struct iphdr);
if (optlen <= 0)
@@ -101,7 +99,7 @@ static int ipv4_find_option(struct net *net, struct sk_buff *skb,
/* Copy the options since __ip_options_compile() modifies
* the options.
*/
- if (skb_copy_bits(skb, start, opt->__data, optlen))
+ if (skb_copy_bits(skb, sizeof(struct iphdr), opt->__data, optlen))
return -EBADMSG;
opt->optlen = optlen;

@@ -116,18 +114,18 @@ static int ipv4_find_option(struct net *net, struct sk_buff *skb,
found = target == IPOPT_SSRR ? opt->is_strictroute :
!opt->is_strictroute;
if (found)
- *offset = opt->srr + start;
+ *offset = opt->srr;
break;
case IPOPT_RR:
if (!opt->rr)
break;
- *offset = opt->rr + start;
+ *offset = opt->rr;
found = true;
break;
case IPOPT_RA:
if (!opt->router_alert)
break;
- *offset = opt->router_alert + start;
+ *offset = opt->router_alert;
found = true;
break;
default:
--
2.39.5