From 2f204fe718f5bf519013cc2536ad7bb2cbb51661 Mon Sep 17 00:00:00 2001 From: Eric Biggers Date: Mon, 22 Jun 2026 16:48:03 -0700 Subject: crypto: af_alg - Add af_alg_restrict sysctl, defaulting to 1 AF_ALG is a frequent source of vulnerabilities and a maintenance nightmare. It exposes far more functionality to userspace than ever should have been exposed, especially to unprivileged processes. Recent exploits have targeted kernel internal implementation details like "authencesn" that have zero use case for userspace access. Fortunately, AF_ALG is rarely used in practice, as userspace crypto libraries exist. And when it is used, only some functionality is known to be used, and many users are known to hold capabilities already. iwd for example requires CAP_NET_ADMIN and has a known algorithm list (https://lore.kernel.org/linux-crypto/bcbbef00-5881-421b-8892-7be6c04b832d@gmail.com/). Thus, let's restrict the set of allowed algorithms by default, depending on the capabilities held. Add a sysctl /proc/sys/crypto/af_alg_restrict with meaning: 0: unrestricted 1: limited functionality 2: completely disabled Set the default value to 1, which enables an algorithm allowlist for unprivileged processes and a slightly longer allowlist for privileged processes. Note that the list may be tweaked in the future. However, the common use cases such as iwd and bluez are taken into account already. I've tested that iwd still works with the default value of 1. Signed-off-by: Eric Biggers Signed-off-by: Herbert Xu --- include/crypto/if_alg.h | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'include') diff --git a/include/crypto/if_alg.h b/include/crypto/if_alg.h index 7643ba954125..4e9ed8e73403 100644 --- a/include/crypto/if_alg.h +++ b/include/crypto/if_alg.h @@ -161,9 +161,17 @@ struct af_alg_ctx { unsigned int inflight; }; +struct af_alg_allowlist_entry { + const char *name; + bool privileged; +}; + int af_alg_register_type(const struct af_alg_type *type); int af_alg_unregister_type(const struct af_alg_type *type); +int af_alg_check_restriction(const char *name, + const struct af_alg_allowlist_entry allowlist[]); + int af_alg_release(struct socket *sock); void af_alg_release_parent(struct sock *sk); int af_alg_accept(struct sock *sk, struct socket *newsock, -- cgit v1.2.3