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Fri, 31 Jul 2026 07:06:58 -0700 (PDT) From: David Lee To: steffen.klassert@secunet.com, herbert@gondor.apana.org.au, davem@davemloft.net, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com Cc: David Lee , Kyle Zeng , Dominik 'Disconnect3d' Czarnota , horms@kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: [PATCH] xfrm: fix compat ALLOCSPI request use-after-free Date: Fri, 31 Jul 2026 14:06:57 +0000 Message-ID: <20260731140658.566571-1-david.lee@trailofbits.com> X-Mailer: git-send-email 2.43.0 Precedence: bulk X-Mailing-List: netdev@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit xfrm_state_netlink() builds the ALLOCSPI response with dump_one_state(), which already calls alloc_compat() with the response skb and header. xfrm_alloc_userspi() then calls alloc_compat() again, but passes the original request skb and its header. For a compat request, the translator therefore interprets the 228-byte compat xfrm_userspi_info as the 232-byte native layout and reads four bytes past the declared payload. It also publishes the translated child through the request's frag_list. A multicast clone of the request shares skb_shared_info and can observe that child. xfrm_user_rcv_msg() frees it after the request handler returns, racing a compat receiver which may still be copying from it and resulting in a use-after-free. Remove the redundant conversion. The response keeps its correct compat translation from dump_one_state(), and no child is attached to the inbound request. Fixes: 5f3eea6b7e8f ("xfrm/compat: Attach xfrm dumps to 64=>32 bit translator") Bug found and triaged by OpenAI Security Research and validated by Trail of Bits. Assisted-by: Codex:gpt-5.6-sol gpt-5.5-cyber Signed-off-by: Kyle Zeng --- Trail of Bits has a reproducer for this bug that triggers a KASAN use-after-free and can share if needed. net/xfrm/xfrm_user.c | 12 ------------ 1 file changed, 12 deletions(-) diff --git a/net/xfrm/xfrm_user.c b/net/xfrm/xfrm_user.c index d6db63304ba6bd5bbd9c09c665170936e1107ced..a7f35a123648d3946aae88674c7bead5666c9eb3 100644 --- a/net/xfrm/xfrm_user.c +++ b/net/xfrm/xfrm_user.c @@ -1877,7 +1877,6 @@ static int xfrm_alloc_userspi(struct sk_buff *skb, struct nlmsghdr *nlh, struct net *net = sock_net(skb->sk); struct xfrm_state *x; struct xfrm_userspi_info *p; - struct xfrm_translator *xtr; struct sk_buff *resp_skb; xfrm_address_t *daddr; int family; @@ -1943,17 +1942,6 @@ static int xfrm_alloc_userspi(struct sk_buff *skb, struct nlmsghdr *nlh, goto out; } - xtr = xfrm_get_translator(); - if (xtr) { - err = xtr->alloc_compat(skb, nlmsg_hdr(skb)); - - xfrm_put_translator(xtr); - if (err) { - kfree_skb(resp_skb); - goto out; - } - } - err = nlmsg_unicast(xfrm_net_nlsk(net, skb), resp_skb, NETLINK_CB(skb).portid); out: -- 2.53.0