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 --- include/net/rtnh.h | 34 ++++++++++++++++++++++++++++++++++ 1 file changed, 34 insertions(+) create mode 100644 include/net/rtnh.h (limited to 'include/net/rtnh.h') diff --git a/include/net/rtnh.h b/include/net/rtnh.h new file mode 100644 index 000000000..aa2cfc508 --- /dev/null +++ b/include/net/rtnh.h @@ -0,0 +1,34 @@ +/* SPDX-License-Identifier: GPL-2.0 */ +#ifndef __NET_RTNH_H +#define __NET_RTNH_H + +#include +#include + +static inline int rtnh_ok(const struct rtnexthop *rtnh, int remaining) +{ + return remaining >= (int)sizeof(*rtnh) && + rtnh->rtnh_len >= sizeof(*rtnh) && + rtnh->rtnh_len <= remaining; +} + +static inline struct rtnexthop *rtnh_next(const struct rtnexthop *rtnh, + int *remaining) +{ + int totlen = NLA_ALIGN(rtnh->rtnh_len); + + *remaining -= totlen; + return (struct rtnexthop *) ((char *) rtnh + totlen); +} + +static inline struct nlattr *rtnh_attrs(const struct rtnexthop *rtnh) +{ + return (struct nlattr *) ((char *) rtnh + NLA_ALIGN(sizeof(*rtnh))); +} + +static inline int rtnh_attrlen(const struct rtnexthop *rtnh) +{ + return rtnh->rtnh_len - NLA_ALIGN(sizeof(*rtnh)); +} + +#endif -- cgit v1.3.1