[PATCH v2 net] ipv4: restrict IPOPT_SSRR and IPOPT_LSRR options

[PATCH v2 net] ipv4: restrict IPOPT_SSRR and IPOPT_LSRR options

[Eric Dumazet]

This patch restricts setting Loose Source and Record Route (LSRR)
and Strict Source and Record Route (SSRR) IP options to users
with CAP_NET_RAW capability.

This prevents unprivileged applications from forcing packets to route
through attacker-controlled nodes to leak TCP ISN and possibly other
protocol information.

While LSRR and SSRR are commonly filtered in many network environments,
they may still be supported and forwarded along some network paths.

RFC 7126 (Recommendations on Filtering of IPv4 Packets Containing
IPv4 Options) recommend to drop these options in 4.3 and 4.4.

Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
Reported-by: Tamir Shahar <tamirthesis@gmail.com>
Reported-by: Amit Klein <aksecurity@gmail.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
---
v2: use Ido's suggestion.
v1: https://lore.kernel.org/netdev/20260601124157.699463-1-edumazet@google.com/

 net/ipv4/ip_options.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/net/ipv4/ip_options.c b/net/ipv4/ip_options.c
index be8815ce3ac242372eeae4a97091cda26d40ceb0..09d745112c1526a1f151cd917f97dc1e236d6d22 100644
--- a/net/ipv4/ip_options.c
+++ b/net/ipv4/ip_options.c
@@ -530,6 +530,10 @@ int ip_options_get(struct net *net, struct ip_options_rcu **optp,
 		kfree(opt);
 		return -EINVAL;
 	}
+	if (opt->opt.srr && !ns_capable(net->user_ns, CAP_NET_RAW)) {
+		kfree(opt);
+		return -EPERM;
+	}
 	kfree(*optp);
 	*optp = opt;
 	return 0;
-- 
2.54.0.929.g9b7fa37559-goog

Re: [PATCH v2 net] ipv4: restrict IPOPT_SSRR and IPOPT_LSRR options

[David Ahern]

On 6/2/26 10:15 AM, Eric Dumazet wrote:
> This patch restricts setting Loose Source and Record Route (LSRR)
> and Strict Source and Record Route (SSRR) IP options to users
> with CAP_NET_RAW capability.
> 
> This prevents unprivileged applications from forcing packets to route
> through attacker-controlled nodes to leak TCP ISN and possibly other
> protocol information.
> 
> While LSRR and SSRR are commonly filtered in many network environments,
> they may still be supported and forwarded along some network paths.
> 
> RFC 7126 (Recommendations on Filtering of IPv4 Packets Containing
> IPv4 Options) recommend to drop these options in 4.3 and 4.4.
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Reported-by: Tamir Shahar <tamirthesis@gmail.com>
> Reported-by: Amit Klein <aksecurity@gmail.com>
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> ---
> v2: use Ido's suggestion.
> v1: https://lore.kernel.org/netdev/20260601124157.699463-1-edumazet@google.com/
> 
>  net/ipv4/ip_options.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 

Reviewed-by: David Ahern <dsahern@kernel.org>

Re: [PATCH v2 net] ipv4: restrict IPOPT_SSRR and IPOPT_LSRR options

[Ido Schimmel]

On Tue, Jun 02, 2026 at 04:15:47PM +0000, Eric Dumazet wrote:
> This patch restricts setting Loose Source and Record Route (LSRR)
> and Strict Source and Record Route (SSRR) IP options to users
> with CAP_NET_RAW capability.
> 
> This prevents unprivileged applications from forcing packets to route
> through attacker-controlled nodes to leak TCP ISN and possibly other
> protocol information.
> 
> While LSRR and SSRR are commonly filtered in many network environments,
> they may still be supported and forwarded along some network paths.
> 
> RFC 7126 (Recommendations on Filtering of IPv4 Packets Containing
> IPv4 Options) recommend to drop these options in 4.3 and 4.4.
> 
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")
> Reported-by: Tamir Shahar <tamirthesis@gmail.com>
> Reported-by: Amit Klein <aksecurity@gmail.com>
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Reviewed-by: Ido Schimmel <idosch@nvidia.com>

Re: [PATCH v2 net] ipv4: restrict IPOPT_SSRR and IPOPT_LSRR options

[patchwork-bot+netdevbpf]

Hello:

This patch was applied to netdev/net.git (main)
by Jakub Kicinski <kuba@kernel.org>:

On Tue,  2 Jun 2026 16:15:47 +0000 you wrote:
> This patch restricts setting Loose Source and Record Route (LSRR)
> and Strict Source and Record Route (SSRR) IP options to users
> with CAP_NET_RAW capability.
> 
> This prevents unprivileged applications from forcing packets to route
> through attacker-controlled nodes to leak TCP ISN and possibly other
> protocol information.
> 
> [...]

Here is the summary with links:
  - [v2,net] ipv4: restrict IPOPT_SSRR and IPOPT_LSRR options
    https://git.kernel.org/netdev/net/c/d3915a1f5a4b

You are awesome, thank you!
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