From 1039bffd6ae9c75b42b7d148d6c1106134107b66 Mon Sep 17 00:00:00 2001 From: Xie Yuanbin Date: Tue, 28 Jul 2026 03:16:42 +0100 Subject: ARM: 9485/1: mm: acquire mmap write lock around show_pte() for user faults When CONFIG_DEBUG_USER=y, and cmdline "user_debug=31" is set, a user fault may trigger show_pte() without any lock. If another thread in the same process concurrently calls munmap(), the page table pages may be freed while show_pte() is still traversing them, causing a use-after-free in show_pte(). If CONFIG_ARM_LPAE=y, this may cause a kernel panic if the pages table of PMD are freed when show_pte() is running. Acquire mmap_write_lock() around show_pte() for user faults to fix the contention. For user faults, additionally restrict that show_pte() is called only when the addr is a user-space address (addr < TASK_SIZE). This is because the lock of tsk->mm only protects the virtual memory of user address space, furthermore, dumping the page tables of a kernel-space address for user faults is unnecessary and may have security implications. Keep everything unchanged for kernel faults, because the kernel is already in the "oops" state, acquiring a lock may risk a deadlock. Co-developed-by: Qi Xi Fixes: 6d021b724481 ("ARM: dump pgd, pmd and pte states on unhandled data abort faults") Link: https://lore.kernel.org/20260716014022.2823-1-xieyuanbin1@huawei.com Acked-by: Lorenzo Stoakes (ARM) Reviewed-by: Linus Walleij Signed-off-by: Qi Xi Signed-off-by: Xie Yuanbin Signed-off-by: Russell King --- samples/bpf/parse_ldabs.c | 43 +++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 43 insertions(+) create mode 100644 samples/bpf/parse_ldabs.c (limited to 'samples/bpf/parse_ldabs.c') diff --git a/samples/bpf/parse_ldabs.c b/samples/bpf/parse_ldabs.c new file mode 100644 index 000000000..c6f65f90a --- /dev/null +++ b/samples/bpf/parse_ldabs.c @@ -0,0 +1,43 @@ +/* Copyright (c) 2016 Facebook + * + * This program is free software; you can redistribute it and/or + * modify it under the terms of version 2 of the GNU General Public + * License as published by the Free Software Foundation. + */ +#define KBUILD_MODNAME "foo" +#include +#include +#include +#include +#include +#include +#include +#include "bpf_legacy.h" + +#define DEFAULT_PKTGEN_UDP_PORT 9 +#define IP_MF 0x2000 +#define IP_OFFSET 0x1FFF + +static inline int ip_is_fragment(struct __sk_buff *ctx, __u64 nhoff) +{ + return load_half(ctx, nhoff + offsetof(struct iphdr, frag_off)) + & (IP_MF | IP_OFFSET); +} + +SEC("ldabs") +int handle_ingress(struct __sk_buff *skb) +{ + __u64 troff = ETH_HLEN + sizeof(struct iphdr); + + if (load_half(skb, offsetof(struct ethhdr, h_proto)) != ETH_P_IP) + return 0; + if (load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)) != IPPROTO_UDP || + load_byte(skb, ETH_HLEN) != 0x45) + return 0; + if (ip_is_fragment(skb, ETH_HLEN)) + return 0; + if (load_half(skb, troff + offsetof(struct udphdr, dest)) == DEFAULT_PKTGEN_UDP_PORT) + return TC_ACT_SHOT; + return 0; +} +char _license[] SEC("license") = "GPL"; -- cgit v1.3.1