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xfrm: Sanitize marks before insert

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Prior to this patch, the mark is sanitized (applying the state's mask to
the state's value) only on inserts when checking if a conflicting XFRM
state or policy exists.

We discovered in Cilium that this same sanitization does not occur
in the hot-path __xfrm_state_lookup. In the hot-path, the sk_buff's mark
is simply compared to the state's value:

    if ((mark & x->mark.m) != x->mark.v)
        continue;

Therefore, users can define unsanitized marks (ex. 0xf42/0xf00) which will
never match any packet.

This commit updates __xfrm_state_insert and xfrm_policy_insert to store
the sanitized marks, thus removing this footgun.

This has the side effect of changing the ip output, as the
returned mark will have the mask applied to it when printed.

Fixes: 3d6acfa764 ("xfrm: SA lookups with mark")
Signed-off-by: Paul Chaignon <paul.chaignon@gmail.com>
Signed-off-by: Louis DeLosSantos <louis.delos.devel@gmail.com>
Co-developed-by: Louis DeLosSantos <louis.delos.devel@gmail.com>
Signed-off-by: Steffen Klassert <steffen.klassert@secunet.com>
This commit is contained in:
Paul Chaignon 2025-05-07 13:31:58 +02:00 • committed by Steffen Klassert
parent 417fae2c40
commit 0b91fda3a1
2 changed files with 6 additions and 0 deletions
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3
net/xfrm/xfrm_policy.c
View file

@ -1581,6 +1581,9 @@ int xfrm_policy_insert(int dir, struct xfrm_policy *policy, int excl)
struct xfrm_policy *delpol;
struct hlist_head *chain;
/* Sanitize mark before store */
policy->mark.v &= policy->mark.m;
spin_lock_bh(&net->xfrm.xfrm_policy_lock);
chain = policy_hash_bysel(net, &policy->selector, policy->family, dir);
if (chain)

3
net/xfrm/xfrm_state.c
View file

@ -1718,6 +1718,9 @@ static void __xfrm_state_insert(struct xfrm_state *x)
list_add(&x->km.all, &net->xfrm.state_all);
/* Sanitize mark before store */
x->mark.v &= x->mark.m;
h = xfrm_dst_hash(net, &x->id.daddr, &x->props.saddr,
x->props.reqid, x->props.family);
XFRM_STATE_INSERT(bydst, &x->bydst, net->xfrm.state_bydst + h,