From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 4B81543D4FB; Tue, 16 Jun 2026 15:47:39 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781624860; cv=none; b=oSNb4AwmtdvERNwonTCB2MeWjGPdKS/+YwT41OxOhiGoZ8loQM0tooQdjUgyZB+Tpq9MiXgdsWPt/tbt32i0EGApfuItwaGAxv2UvNxVfteW427grFjVLUxes3NN055ISZMmBDxcLFMtQWYGwRHR1ovbMmJtONkFRAkAWer1yCg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1781624860; c=relaxed/simple; bh=3AZAxJRRWmFNU1R8Rg1bFouxxGr1k/SixjBc01vHWlo=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=cTJsA5uH0zow1CuuP/CXasuDHhNWfk/1vmhcORj2VkeIjk3SDIGnKq/N9u/fRXGXHYOWF0IEMs7hk5lyqkS+u7AlUtadKRGrK9xkYnMaJK3iY/b4EUYeuZTGrdsB1IgO1rdIkIJ09IrfOvciRlp6zonR9ziyRvq/co62TEBUHco= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=p8oyFc08; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="p8oyFc08" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 37CBA1F00A3A; Tue, 16 Jun 2026 15:47:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linuxfoundation.org; s=korg; t=1781624859; bh=0OPcPYIlw7qxdrVpWSc/7llcdCpTAgGc7B4eI/xJ7Po=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=p8oyFc08n12ARJsQyjM/gpoAI3aQDLqTDP4Y52fJ+n/zevwrzPx1ReydSNMoJ/m09 wzz614Ca564mgUxb62fGKVH9XlaeIxKbMIXnscMxzUpjuvisVpLLYVreqP+NhapUhK yE2YyyONKPglTIZcW+4ihbOVP7OiV3Tm72FihGJo= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, syzbot+819eb928d120d2bdad0e@syzkaller.appspotmail.com, Kuniyuki Iwashima , Jiayuan Chen , Ido Schimmel , Jakub Kicinski , Sasha Levin Subject: [PATCH 6.18 040/325] ipv6: anycast: insert aca into global hash under idev->lock Date: Tue, 16 Jun 2026 20:27:16 +0530 Message-ID: <20260616145059.729462880@linuxfoundation.org> X-Mailer: git-send-email 2.54.0 In-Reply-To: <20260616145057.827196531@linuxfoundation.org> References: <20260616145057.827196531@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.18-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jiayuan Chen [ Upstream commit f723ccaff2fb72b71ae8a9fd283f0dee4d9ae7a3 ] syzbot reported a splat [1]: a slab-use-after-free in ipv6_chk_acast_addr(), which walks the global inet6_acaddr_lst[] hash under RCU and dereferences a struct ifacaddr6 that has already been freed while still linked in the hash, so a later reader walks into a dangling node. In __ipv6_dev_ac_inc() the aca is allocated with refcount 1, then aca_get() bumps it to 2 to keep it alive across the unlocked region. It is published to idev->ac_list under idev->lock, but ipv6_add_acaddr_hash() runs after write_unlock_bh(). A concurrent teardown (ipv6_ac_destroy_dev() from addrconf_ifdown(), under RTNL) can slip into that window: CPU0 __ipv6_dev_ac_inc CPU1 ipv6_ac_destroy_dev (RTNL) ------------------------------ ------------------------------------ aca_alloc() refcnt 1 aca_get() refcnt 2 write_lock_bh(idev->lock) add aca to ac_list write_unlock_bh(idev->lock) write_lock_bh(idev->lock) pull aca off ac_list write_unlock_bh(idev->lock) ipv6_del_acaddr_hash(aca) hlist_del_init_rcu() is a no-op, aca is not in the hash yet aca_put() refcnt 2->1 ipv6_add_acaddr_hash(aca) aca now inserted into the hash aca_put() refcnt 1->0 call_rcu(aca_free_rcu) -> kfree(aca) The hash removal becomes a no-op because the insertion has not happened yet, so once CPU0 inserts and drops the last reference, the aca is freed while still linked in inet6_acaddr_lst[], and readers dereference freed memory after the slab slot is reused. This window opened once RTNL stopped serializing the join path against device teardown. Move ipv6_add_acaddr_hash() inside the idev->lock section so the ac_list and hash insertions are atomic with respect to teardown: a racing remover now either misses the aca entirely or finds it in both lists. acaddr_hash_lock is now nested under idev->lock, which is acquired in softirq context, so switch all acaddr_hash_lock sites to spin_lock_bh() to avoid the irq lock inversion reported in [2]. [1] https://syzkaller.appspot.com/bug?extid=a01df04303c131efbf3a [2] https://lore.kernel.org/netdev/6a194ef7.ba3b1513.1890b4.0000.GAE@google.com/ Reported-by: syzbot+819eb928d120d2bdad0e@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/6a191f87.ce022c6e.138e56.0003.GAE@google.com/T/ Reviewed-by: Kuniyuki Iwashima Fixes: eb1ac9ff6c4a ("ipv6: anycast: Don't hold RTNL for IPV6_JOIN_ANYCAST.") Signed-off-by: Jiayuan Chen Reviewed-by: Ido Schimmel Link: https://patch.msgid.link/20260529152219.235475-1-jiayuan.chen@linux.dev Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- net/ipv6/anycast.c | 16 ++++++++-------- 1 file changed, 8 insertions(+), 8 deletions(-) diff --git a/net/ipv6/anycast.c b/net/ipv6/anycast.c index 52599584422bf4..819c4ff10997e0 100644 --- a/net/ipv6/anycast.c +++ b/net/ipv6/anycast.c @@ -243,16 +243,16 @@ static void ipv6_add_acaddr_hash(struct net *net, struct ifacaddr6 *aca) { unsigned int hash = inet6_acaddr_hash(net, &aca->aca_addr); - spin_lock(&acaddr_hash_lock); + spin_lock_bh(&acaddr_hash_lock); hlist_add_head_rcu(&aca->aca_addr_lst, &inet6_acaddr_lst[hash]); - spin_unlock(&acaddr_hash_lock); + spin_unlock_bh(&acaddr_hash_lock); } static void ipv6_del_acaddr_hash(struct ifacaddr6 *aca) { - spin_lock(&acaddr_hash_lock); + spin_lock_bh(&acaddr_hash_lock); hlist_del_init_rcu(&aca->aca_addr_lst); - spin_unlock(&acaddr_hash_lock); + spin_unlock_bh(&acaddr_hash_lock); } static void aca_get(struct ifacaddr6 *aca) @@ -371,10 +371,10 @@ int __ipv6_dev_ac_inc(struct inet6_dev *idev, const struct in6_addr *addr) aca->aca_next = idev->ac_list; rcu_assign_pointer(idev->ac_list, aca); - write_unlock_bh(&idev->lock); - ipv6_add_acaddr_hash(net, aca); + write_unlock_bh(&idev->lock); + ip6_ins_rt(net, f6i); addrconf_join_solict(idev->dev, &aca->aca_addr); @@ -649,8 +649,8 @@ void ipv6_anycast_cleanup(void) { int i; - spin_lock(&acaddr_hash_lock); + spin_lock_bh(&acaddr_hash_lock); for (i = 0; i < IN6_ADDR_HSIZE; i++) WARN_ON(!hlist_empty(&inet6_acaddr_lst[i])); - spin_unlock(&acaddr_hash_lock); + spin_unlock_bh(&acaddr_hash_lock); } -- 2.53.0