From 7bff3c06997374fb9b9991536a547b840549a813 Mon Sep 17 00:00:00 2001 From: Qian Cai Date: Tue, 8 Jan 2019 15:23:04 -0800 Subject: [PATCH] mm/usercopy.c: no check page span for stack objects It is easy to trigger this with CONFIG_HARDENED_USERCOPY_PAGESPAN=y, usercopy: Kernel memory overwrite attempt detected to spans multiple pages (offset 0, size 23)! kernel BUG at mm/usercopy.c:102! For example, print_worker_info char name[WQ_NAME_LEN] = { }; char desc[WORKER_DESC_LEN] = { }; probe_kernel_read(name, wq->name, sizeof(name) - 1); probe_kernel_read(desc, worker->desc, sizeof(desc) - 1); __copy_from_user_inatomic check_object_size check_heap_object check_page_span This is because on-stack variables could cross PAGE_SIZE boundary, and failed this check, if (likely(((unsigned long)ptr & (unsigned long)PAGE_MASK) == ((unsigned long)end & (unsigned long)PAGE_MASK))) ptr = FFFF889007D7EFF8 end = FFFF889007D7F00E Hence, fix it by checking if it is a stack object first. [keescook@chromium.org: improve comments after reorder] Link: http://lkml.kernel.org/r/20190103165151.GA32845@beast Link: http://lkml.kernel.org/r/20181231030254.99441-1-cai@lca.pw Signed-off-by: Qian Cai Signed-off-by: Kees Cook Acked-by: Kees Cook Cc: Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/usercopy.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/mm/usercopy.c b/mm/usercopy.c index 852eb4e53f06..14faadcedd06 100644 --- a/mm/usercopy.c +++ b/mm/usercopy.c @@ -247,7 +247,8 @@ static DEFINE_STATIC_KEY_FALSE_RO(bypass_usercopy_checks); /* * Validates that the given object is: * - not bogus address - * - known-safe heap or stack object + * - fully contained by stack (or stack frame, when available) + * - fully within SLAB object (or object whitelist area, when available) * - not in kernel text */ void __check_object_size(const void *ptr, unsigned long n, bool to_user) @@ -262,9 +263,6 @@ void __check_object_size(const void *ptr, unsigned long n, bool to_user) /* Check for invalid addresses. */ check_bogus_address((const unsigned long)ptr, n, to_user); - /* Check for bad heap object. */ - check_heap_object(ptr, n, to_user); - /* Check for bad stack object. */ switch (check_stack_object(ptr, n)) { case NOT_STACK: @@ -282,6 +280,9 @@ void __check_object_size(const void *ptr, unsigned long n, bool to_user) usercopy_abort("process stack", NULL, to_user, 0, n); } + /* Check for bad heap object. */ + check_heap_object(ptr, n, to_user); + /* Check for object in kernel to avoid text exposure. */ check_kernel_text_object((const unsigned long)ptr, n, to_user); }