From a7cb5d23eaea148f8582229846f8dfff192f05c3 Mon Sep 17 00:00:00 2001 From: Marco Elver Date: Thu, 19 Aug 2021 19:04:30 -0700 Subject: [PATCH] kfence: fix is_kfence_address() for addresses below KFENCE_POOL_SIZE Originally the addr != NULL check was meant to take care of the case where __kfence_pool == NULL (KFENCE is disabled). However, this does not work for addresses where addr > 0 && addr < KFENCE_POOL_SIZE. This can be the case on NULL-deref where addr > 0 && addr < PAGE_SIZE or any other faulting access with addr < KFENCE_POOL_SIZE. While the kernel would likely crash, the stack traces and report might be confusing due to double faults upon KFENCE's attempt to unprotect such an address. Fix it by just checking that __kfence_pool != NULL instead. Link: https://lkml.kernel.org/r/20210818130300.2482437-1-elver@google.com Fixes: 0ce20dd84089 ("mm: add Kernel Electric-Fence infrastructure") Signed-off-by: Marco Elver Reported-by: Kuan-Ying Lee Acked-by: Alexander Potapenko Cc: Dmitry Vyukov Cc: [5.12+] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- include/linux/kfence.h | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/include/linux/kfence.h b/include/linux/kfence.h index a70d1ea..3fe6dd8 100644 --- a/include/linux/kfence.h +++ b/include/linux/kfence.h @@ -51,10 +51,11 @@ extern atomic_t kfence_allocation_gate; static __always_inline bool is_kfence_address(const void *addr) { /* - * The non-NULL check is required in case the __kfence_pool pointer was - * never initialized; keep it in the slow-path after the range-check. + * The __kfence_pool != NULL check is required to deal with the case + * where __kfence_pool == NULL && addr < KFENCE_POOL_SIZE. Keep it in + * the slow-path after the range-check! */ - return unlikely((unsigned long)((char *)addr - __kfence_pool) < KFENCE_POOL_SIZE && addr); + return unlikely((unsigned long)((char *)addr - __kfence_pool) < KFENCE_POOL_SIZE && __kfence_pool); } /** -- 2.7.4